[Script Info]
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[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.52,0:00:03.40,Default,,0000,0000,0000,,See how confident you are with the Wolverines.
Dialogue: 0,0:00:03.40,0:00:07.00,Default,,0000,0000,0000,,Okay. So we’ve talked about urban air pollution
Dialogue: 0,0:00:07.00,0:00:09.14,Default,,0000,0000,0000,,a couple of times through this semester
Dialogue: 0,0:00:09.14,0:00:11.98,Default,,0000,0000,0000,,and this is actually a photograph of a typical day in Beijing.
Dialogue: 0,0:00:11.98,0:00:14.81,Default,,0000,0000,0000,,We saw the one a couple of lectures ago
Dialogue: 0,0:00:14.81,0:00:19.14,Default,,0000,0000,0000,,when someone was trying to raise a flag in Tiananmen Square and I,
Dialogue: 0,0:00:19.14,0:00:20.74,Default,,0000,0000,0000,,I couldn’t see the flag.
Dialogue: 0,0:00:20.74,0:00:22.67,Default,,0000,0000,0000,,But you know following a rainfall,
Dialogue: 0,0:00:22.67,0:00:26.48,Default,,0000,0000,0000,,Beijing can clear up and so what we’re going to talk about today
Dialogue: 0,0:00:26.48,0:00:30.60,Default,,0000,0000,0000,,are some of the causes of urban air pollution,
Dialogue: 0,0:00:30.60,0:00:34.07,Default,,0000,0000,0000,,specifically around smog and photochemical smog.
Dialogue: 0,0:00:34.07,0:00:38.56,Default,,0000,0000,0000,,So what we’ll talk about today again will be
Dialogue: 0,0:00:38.56,0:00:41.54,Default,,0000,0000,0000,,some of the primary pollutants of concern.
Dialogue: 0,0:00:41.54,0:00:44.23,Default,,0000,0000,0000,,Criteria air pollutants as we call them
Dialogue: 0,0:00:44.23,0:00:48.15,Default,,0000,0000,0000,,in the regulatory framework of the U.S. CPA.
Dialogue: 0,0:00:48.15,0:00:53.56,Default,,0000,0000,0000,,We’re going to be able to do calculations using
Dialogue: 0,0:00:53.56,0:00:56.74,Default,,0000,0000,0000,,mass balance equations just like we did earlier,
Dialogue: 0,0:00:56.74,0:01:01.74,Default,,0000,0000,0000,,whether it was for a, you know earlier we looked at lakes and creeks merging.
Dialogue: 0,0:01:01.74,0:01:03.90,Default,,0000,0000,0000,,We looked at reactors.
Dialogue: 0,0:01:03.90,0:01:07.90,Default,,0000,0000,0000,,We’re going to look at an urban box model for air pollution
Dialogue: 0,0:01:07.90,0:01:10.40,Default,,0000,0000,0000,,and we’ll do similar sorts of calculations
Dialogue: 0,0:01:10.40,0:01:12.56,Default,,0000,0000,0000,,looking at pollutants in and out,
Dialogue: 0,0:01:12.56,0:01:17.23,Default,,0000,0000,0000,,and those that can be generated within that volume.
Dialogue: 0,0:01:17.23,0:01:21.98,Default,,0000,0000,0000,,We’ll talk a bit about the mechanisms of photochemical smog formation.
Dialogue: 0,0:01:21.98,0:01:24.14,Default,,0000,0000,0000,,You may remember a couple of lectures ago
Dialogue: 0,0:01:24.14,0:01:27.14,Default,,0000,0000,0000,,we talked about good ozone and bad ozone,
Dialogue: 0,0:01:27.14,0:01:30.54,Default,,0000,0000,0000,,and the focus today will be on the bad ozone,
Dialogue: 0,0:01:30.54,0:01:33.20,Default,,0000,0000,0000,,the ozone in the troposphere.
Dialogue: 0,0:01:33.20,0:01:36.48,Default,,0000,0000,0000,,We’ll finish up with some discussion of isopleth diagrams
Dialogue: 0,0:01:36.48,0:01:39.48,Default,,0000,0000,0000,,and ozone forming potential, and that will give you
Dialogue: 0,0:01:39.48,0:01:43.15,Default,,0000,0000,0000,,an idea of perhaps some management tools
Dialogue: 0,0:01:43.15,0:01:48.56,Default,,0000,0000,0000,,for looking at reducing NOx or VOCs and formation of photochemical smog.
Dialogue: 0,0:01:48.56,0:01:52.67,Default,,0000,0000,0000,,And we’ll talk about a nice little calculation tool at the end of the lecture,
Dialogue: 0,0:01:52.67,0:01:56.54,Default,,0000,0000,0000,,the MIR, the maximum incremental reactivity scale.
Dialogue: 0,0:01:56.54,0:02:02.27,Default,,0000,0000,0000,,It gives us a way to look at some individual VOCs and their potential for ozone formation.
Dialogue: 0,0:02:02.27,0:02:09.34,Default,,0000,0000,0000,,Okay so we have talked about the primary air contaminants
Dialogue: 0,0:02:09.34,0:02:13.14,Default,,0000,0000,0000,,of concern in urban environments and criteria air pollutants.
Dialogue: 0,0:02:13.14,0:02:16.20,Default,,0000,0000,0000,,So you may remember this figure.
Dialogue: 0,0:02:16.20,0:02:34.81,Default,,0000,0000,0000,,So we talked about sources of air pollution.
Dialogue: 0,0:02:34.81,0:02:39.48,Default,,0000,0000,0000,,Of course, coal burning power plants, ones that are very prevalent in China,
Dialogue: 0,0:02:39.48,0:02:45.40,Default,,0000,0000,0000,,are responsible for emitting SOx and NOx and particulates and hydrocarbons,
Dialogue: 0,0:02:45.40,0:02:48.54,Default,,0000,0000,0000,,and those are all criteria air pollutants.
Dialogue: 0,0:02:48.54,0:02:54.34,Default,,0000,0000,0000,,Urban transportation, motor vehicles are also significant sources of admissions
Dialogue: 0,0:02:54.34,0:02:59.34,Default,,0000,0000,0000,,of both NOx and hydrocarbons, particularly carbon monoxide
Dialogue: 0,0:02:59.34,0:03:02.56,Default,,0000,0000,0000,,and other partially burned fuels.
Dialogue: 0,0:03:02.56,0:03:08.94,Default,,0000,0000,0000,,Incinerators, other industrial stacks, can be sources of air pollution as well.
Dialogue: 0,0:03:08.94,0:03:12.74,Default,,0000,0000,0000,,So there are a number of sources to consider.
Dialogue: 0,0:03:12.74,0:03:16.74,Default,,0000,0000,0000,,When we do some of our box model monitor, modeling,
Dialogue: 0,0:03:16.74,0:03:21.00,Default,,0000,0000,0000,,of course we’re going to be looking at things at a fairly large scale.
Dialogue: 0,0:03:21.00,0:03:23.07,Default,,0000,0000,0000,,But as you reduce your scale,
Dialogue: 0,0:03:23.07,0:03:27.60,Default,,0000,0000,0000,,if you become the environmental engineer at an industrial facility,
Dialogue: 0,0:03:27.60,0:03:31.54,Default,,0000,0000,0000,,and someone tells you we’re going to put another stack out the roof
Dialogue: 0,0:03:31.54,0:03:33.31,Default,,0000,0000,0000,,because we’re going to add a new process,
Dialogue: 0,0:03:33.31,0:03:36.20,Default,,0000,0000,0000,,well then you have to look at the impact of that stack and
Dialogue: 0,0:03:36.20,0:03:40.06,Default,,0000,0000,0000,,its emissions on the ambient air.
Dialogue: 0,0:03:40.06,0:03:42.81,Default,,0000,0000,0000,,Are you going to be increasing NOx?
Dialogue: 0,0:03:42.81,0:03:46.90,Default,,0000,0000,0000,,Are you going to be increasing VOCs at the property boundary?
Dialogue: 0,0:03:46.90,0:03:53.07,Default,,0000,0000,0000,,So we talked earlier about the major criteria air pollutants,
Dialogue: 0,0:03:53.07,0:03:59.07,Default,,0000,0000,0000,,carbon monoxide and O2 ozone, SO2, lead, and particulate matter.
Dialogue: 0,0:03:59.07,0:04:02.31,Default,,0000,0000,0000,,The focus today will be a lot on NO2,
Dialogue: 0,0:04:02.31,0:04:08.23,Default,,0000,0000,0000,,which is responsible for photochemical smog, the resultant pollutant ozone,
Dialogue: 0,0:04:08.23,0:04:12.23,Default,,0000,0000,0000,,and other VOCs that are CAPs.
Dialogue: 0,0:04:12.23,0:04:15.23,Default,,0000,0000,0000,,Another term you may hear in the air pollution vernacular
Dialogue: 0,0:04:15.23,0:04:17.73,Default,,0000,0000,0000,,is HAPs or hazardous air pollutants.
Dialogue: 0,0:04:17.73,0:04:24.60,Default,,0000,0000,0000,,These are typically going to be VOCs like benzene or aldehydes,
Dialogue: 0,0:04:24.60,0:04:28.94,Default,,0000,0000,0000,,other, other volatile organic compounds, heavy metals,
Dialogue: 0,0:04:28.94,0:04:33.60,Default,,0000,0000,0000,,and other pollutants that are emitted at much smaller doses.
Dialogue: 0,0:04:33.60,0:04:38.14,Default,,0000,0000,0000,,But typically an air permitting authority would look at
Dialogue: 0,0:04:38.14,0:04:43.81,Default,,0000,0000,0000,,the total sum of all the HAPs in that emission rather than individual HAPs.
Dialogue: 0,0:04:43.81,0:04:50.23,Default,,0000,0000,0000,,So we have, we’ll start with a, a mass balance problem,
Dialogue: 0,0:04:50.23,0:04:54.27,Default,,0000,0000,0000,,much like we did earlier in, in looking at water.
Dialogue: 0,0:04:54.27,0:05:04.81,Default,,0000,0000,0000,,So we have a city with a given area that has a daily lead emission rate of 5,000 kg/d.
Dialogue: 0,0:05:04.81,0:05:10.00,Default,,0000,0000,0000,,Typically, those would be from auto exhaust and other industrial processes.
Dialogue: 0,0:05:10.00,0:05:16.27,Default,,0000,0000,0000,,Background concentrations of lead we’re going to be given at .1 mcg/m3.
Dialogue: 0,0:05:16.27,0:05:19.81,Default,,0000,0000,0000,,Now during a hot summer day we have a mixing height of 500 meters
Dialogue: 0,0:05:19.81,0:05:22.34,Default,,0000,0000,0000,,and a wind speed of 2 m/s.
Dialogue: 0,0:05:22.34,0:05:25.14,Default,,0000,0000,0000,,So you’ll see when we set up the box model those are variables
Dialogue: 0,0:05:25.14,0:05:29.00,Default,,0000,0000,0000,,that we need to look at a mass balance and a flow of air
Dialogue: 0,0:05:29.00,0:05:32.34,Default,,0000,0000,0000,,through a given control volume.
Dialogue: 0,0:05:32.34,0:05:37.67,Default,,0000,0000,0000,,So we have emissions of lead at 5,000 kg/d,
Dialogue: 0,0:05:37.67,0:05:44.23,Default,,0000,0000,0000,,but we also have lead deposition from the atmosphere at .05 cm/s.
Dialogue: 0,0:05:44.23,0:05:49.65,Default,,0000,0000,0000,,So our question is what is the steady state lead concentration in the urban air?
Dialogue: 0,0:05:49.65,0:05:52.48,Default,,0000,0000,0000,,So remember when we started to talk about mass balance equations,
Dialogue: 0,0:05:52.48,0:05:54.74,Default,,0000,0000,0000,,you have to get into your mind the thought that
Dialogue: 0,0:05:54.74,0:05:58.74,Default,,0000,0000,0000,,is this steady state or non-steady state?
Dialogue: 0,0:05:58.74,0:06:03.07,Default,,0000,0000,0000,,Is this a conservative pollutant or a non-conservative pollutant?
Dialogue: 0,0:06:03.07,0:06:05.23,Default,,0000,0000,0000,,So with the information we have here,
Dialogue: 0,0:06:05.23,0:06:10.34,Default,,0000,0000,0000,,everybody raise your hand who thinks this is a steady state problem?
Dialogue: 0,0:06:10.34,0:06:15.56,Default,,0000,0000,0000,,Please more hands or else you’re going to have a rough time in two weeks.
Dialogue: 0,0:06:15.56,0:06:19.65,Default,,0000,0000,0000,,Okay. This is a definite, we’re asking what’s the steady state lead concentration.
Dialogue: 0,0:06:19.65,0:06:23.67,Default,,0000,0000,0000,,Second question, is this is a conservative or a non-conservative pollutant?
Dialogue: 0,0:06:23.67,0:06:26.14,Default,,0000,0000,0000,,Conservative, raise your hands.
Dialogue: 0,0:06:26.14,0:06:30.56,Default,,0000,0000,0000,,Okay. This, this is a conservative pollutant.
Dialogue: 0,0:06:30.56,0:06:32.74,Default,,0000,0000,0000,,We’re not transforming lead.
Dialogue: 0,0:06:32.74,0:06:34.00,Default,,0000,0000,0000,,We’re not degrading lead.
Dialogue: 0,0:06:34.00,0:06:37.81,Default,,0000,0000,0000,,Now it, it’s going to be emitted and it’s going to be deposited,
Dialogue: 0,0:06:37.81,0:06:39.67,Default,,0000,0000,0000,,and that’s going to be part of our mass balance equation,
Dialogue: 0,0:06:39.67,0:06:44.74,Default,,0000,0000,0000,,but we’re not going to be changing the form of lead in the, in the problem.
Dialogue: 0,0:06:44.74,0:06:47.74,Default,,0000,0000,0000,,Okay, so this is our box model.
Dialogue: 0,0:06:47.74,0:06:51.74,Default,,0000,0000,0000,,And we we’re given the area of Leadville,
Dialogue: 0,0:06:51.74,0:06:55.27,Default,,0000,0000,0000,,so those will be inputs into our calculations.
Dialogue: 0,0:06:55.27,0:07:03.40,Default,,0000,0000,0000,,We set up an atmospheric mixing height that was given in the problem as 500 meters.
Dialogue: 0,0:07:03.40,0:07:06.81,Default,,0000,0000,0000,,So we have our control volume for the air pollution problem.
Dialogue: 0,0:07:06.81,0:07:12.00,Default,,0000,0000,0000,,It’s going to be the area of the city times the mixing height of the problem.
Dialogue: 0,0:07:12.00,0:07:14.23,Default,,0000,0000,0000,,So we have our control volume.
Dialogue: 0,0:07:14.23,0:07:18.48,Default,,0000,0000,0000,,We will have a wind velocity going in and out of that control volume.
Dialogue: 0,0:07:18.48,0:07:21.81,Default,,0000,0000,0000,,We were given a pollutant emission rate M,
Dialogue: 0,0:07:21.81,0:07:24.67,Default,,0000,0000,0000,,that was for lead in kilograms per day.
Dialogue: 0,0:07:24.67,0:07:28.94,Default,,0000,0000,0000,,We also have a pollutant deposition velocity Vd.
Dialogue: 0,0:07:28.94,0:07:33.15,Default,,0000,0000,0000,,So those are the, the parameters around the control volume.
Dialogue: 0,0:07:33.15,0:07:37.48,Default,,0000,0000,0000,,So as we did before, we can set up a mass balance equation
Dialogue: 0,0:07:37.48,0:07:42.87,Default,,0000,0000,0000,,looking at the change of mass over time being equal to the mass in minus the mass out,
Dialogue: 0,0:07:42.87,0:07:46.40,Default,,0000,0000,0000,,plus whatever mass is reacted.
Dialogue: 0,0:07:46.40,0:07:49.54,Default,,0000,0000,0000,,So we said this was a steady state problem,
Dialogue: 0,0:07:49.54,0:07:52.87,Default,,0000,0000,0000,,so the dm/dt is going to be equal to 0.
Dialogue: 0,0:07:52.87,0:07:57.34,Default,,0000,0000,0000,,Lead is not going to be transformed in this problem.
Dialogue: 0,0:07:57.34,0:08:02.15,Default,,0000,0000,0000,,We’re not, it’s not going to be reduced or oxidized.
Dialogue: 0,0:08:02.15,0:08:05.33,Default,,0000,0000,0000,,It’s, it’s not changing any, any forms,
Dialogue: 0,0:08:05.33,0:08:09.48,Default,,0000,0000,0000,,so we’ll have masses going in and out as part of the mass balance,
Dialogue: 0,0:08:09.48,0:08:11.65,Default,,0000,0000,0000,,but no reaction of lead.
Dialogue: 0,0:08:11.65,0:08:16.94,Default,,0000,0000,0000,,So the first thing we can do is a mass balance on the air.
Dialogue: 0,0:08:16.94,0:08:18.94,Default,,0000,0000,0000,,If you remember when we did these water problems,
Dialogue: 0,0:08:18.94,0:08:21.94,Default,,0000,0000,0000,,the first thing we did was look at the mass balance on the water,
Dialogue: 0,0:08:21.94,0:08:24.74,Default,,0000,0000,0000,,and the mass balance on the air is going to be pretty straightforward.
Dialogue: 0,0:08:24.74,0:08:28.07,Default,,0000,0000,0000,,It’s going to be the flow times the density of air.
Dialogue: 0,0:08:28.07,0:08:32.94,Default,,0000,0000,0000,,The mass of air going out is going to be the flow out times the density of air going out,
Dialogue: 0,0:08:32.94,0:08:35.94,Default,,0000,0000,0000,,and we can set these equal to each other.
Dialogue: 0,0:08:35.94,0:08:42.31,Default,,0000,0000,0000,,We know mass in is going to equal mass out and we can substitute a term,
Dialogue: 0,0:08:42.31,0:08:45.98,Default,,0000,0000,0000,,rather than the flow times the density we can use the,
Dialogue: 0,0:08:45.98,0:08:52.94,Default,,0000,0000,0000,,the velocity times the, times the cross-sectional area.
Dialogue: 0,0:08:52.94,0:08:57.07,Default,,0000,0000,0000,,Okay, so our next step is to look at the mass balance on the pollutant.
Dialogue: 0,0:08:57.07,0:09:00.40,Default,,0000,0000,0000,,So again, looking at this mass balance model,
Dialogue: 0,0:09:00.40,0:09:03.40,Default,,0000,0000,0000,,again our flow in is going to be flow out.
Dialogue: 0,0:09:03.40,0:09:05.40,Default,,0000,0000,0000,,So we’ve, we’ve settled that.
Dialogue: 0,0:09:05.40,0:09:09.67,Default,,0000,0000,0000,,So our mass going into our control volume is going to be
Dialogue: 0,0:09:09.67,0:09:16.93,Default,,0000,0000,0000,,the flow times the concentration coming in plus M, our mass emissions rate.
Dialogue: 0,0:09:16.93,0:09:21.67,Default,,0000,0000,0000,,So we have lead in the background that’s coming into our control volume
Dialogue: 0,0:09:21.67,0:09:25.60,Default,,0000,0000,0000,,and we have a lead emission rate within that control volume.
Dialogue: 0,0:09:25.60,0:09:30.48,Default,,0000,0000,0000,,Our mass leaving that control volume will be the flow times
Dialogue: 0,0:09:30.48,0:09:38.23,Default,,0000,0000,0000,,the concentration going out at that border plus the depositional velocity times
Dialogue: 0,0:09:38.23,0:09:43.07,Default,,0000,0000,0000,,the cross-sectional area of that city times the concentration.
Dialogue: 0,0:09:43.07,0:09:46.60,Default,,0000,0000,0000,,So again, we said this was going to be a steady state problem,
Dialogue: 0,0:09:46.60,0:09:49.81,Default,,0000,0000,0000,,so mass in is going to equal mass out.
Dialogue: 0,0:09:49.81,0:09:52.47,Default,,0000,0000,0000,,So we can substitute a few terms.
Dialogue: 0,0:09:52.47,0:09:59.07,Default,,0000,0000,0000,,Rather than Q we can use the cross-sectional velocity or
Dialogue: 0,0:09:59.07,0:10:04.34,Default,,0000,0000,0000,,the wind velocity times the cross-sectional area of the Leadville,
Dialogue: 0,0:10:04.34,0:10:08.67,Default,,0000,0000,0000,,substituting that for Q and so again we set up terms mass in,
Dialogue: 0,0:10:08.67,0:10:14.81,Default,,0000,0000,0000,,concentration plus the emission rate, mass out,
Dialogue: 0,0:10:14.81,0:10:19.34,Default,,0000,0000,0000,,flow times concentration out plus the depositional rate.
Dialogue: 0,0:10:19.34,0:10:21.90,Default,,0000,0000,0000,,So again, lead is not being transformed.
Dialogue: 0,0:10:21.90,0:10:25.40,Default,,0000,0000,0000,,It’s either physically coming in or out of the system.
Dialogue: 0,0:10:25.40,0:10:32.67,Default,,0000,0000,0000,,Okay, so we can set up our mass balance equation
Dialogue: 0,0:10:32.67,0:10:36.60,Default,,0000,0000,0000,,for the pollutant that the mass in is going to be the mass out.
Dialogue: 0,0:10:36.60,0:10:41.74,Default,,0000,0000,0000,,We can rearrange terms and solve for concentration out.
Dialogue: 0,0:10:41.74,0:10:44.07,Default,,0000,0000,0000,,We didn’t carry all the units,
Dialogue: 0,0:10:44.07,0:10:48.81,Default,,0000,0000,0000,,but at home make sure that you double check that you carry the units through
Dialogue: 0,0:10:48.81,0:10:52.56,Default,,0000,0000,0000,,and that they’ve been cancelled out properly.
Dialogue: 0,0:10:52.56,0:10:58.48,Default,,0000,0000,0000,,And we get a concentration out at .55 mcg/m3.
Dialogue: 0,0:10:58.48,0:11:02.15,Default,,0000,0000,0000,,Okay, so very similar to the problems we solved before.
Dialogue: 0,0:11:02.15,0:11:08.90,Default,,0000,0000,0000,,Steady state conservative pollutant so we can set the mass in equal to the mass out.
Dialogue: 0,0:11:08.90,0:11:10.56,Default,,0000,0000,0000,,The only thing that’s a little different here is
Dialogue: 0,0:11:10.56,0:11:13.77,Default,,0000,0000,0000,,you have to make sure you understand how we set up the control volume
Dialogue: 0,0:11:13.77,0:11:18.07,Default,,0000,0000,0000,,and that we are given a mass emission rate and lead deposition rate.
Dialogue: 0,0:11:18.07,0:11:21.14,Default,,0000,0000,0000,,So those are again in and out of the system.
Dialogue: 0,0:11:21.14,0:11:25.73,Default,,0000,0000,0000,,Okay, any questions on setting up a mass balance for air?
Dialogue: 0,0:11:25.73,0:11:27.94,Default,,0000,0000,0000,,It’s a control volume like anything else.
Dialogue: 0,0:11:27.94,0:11:31.90,Default,,0000,0000,0000,,We just have to make sure that when you do these calculations
Dialogue: 0,0:11:31.90,0:11:34.20,Default,,0000,0000,0000,,that you carry the units properly.
Dialogue: 0,0:11:34.20,0:11:39.56,Default,,0000,0000,0000,,You may be given units to convert in an exam problem.
Dialogue: 0,0:11:39.56,0:11:44.20,Default,,0000,0000,0000,,So you have to understand how to do that. Okay.
Dialogue: 0,0:11:44.20,0:11:49.27,Default,,0000,0000,0000,,So we if we look at the way our, our mass balance equation
Dialogue: 0,0:11:49.27,0:11:54.94,Default,,0000,0000,0000,,is set up in terms of Cout, the question is how can we lower that Cout?
Dialogue: 0,0:11:54.94,0:11:59.94,Default,,0000,0000,0000,,You know if we want to reduce lead emissions there are a couple obvious answers.
Dialogue: 0,0:11:59.94,0:12:03.67,Default,,0000,0000,0000,,I mean we certainly can reduce the mass emissions rate.
Dialogue: 0,0:12:03.67,0:12:07.87,Default,,0000,0000,0000,,You know if we reduce M, then Cout is going to be reduced.
Dialogue: 0,0:12:07.87,0:12:13.20,Default,,0000,0000,0000,,The other opportunity here is if we have a very low, low background.
Dialogue: 0,0:12:13.20,0:12:17.48,Default,,0000,0000,0000,,If we increase Z, the mixing height or the wind velocity,
Dialogue: 0,0:12:17.48,0:12:20.74,Default,,0000,0000,0000,,it will also reduce the concentration going out.
Dialogue: 0,0:12:20.74,0:12:23.90,Default,,0000,0000,0000,,So you know we don’t have control over these issues,
Dialogue: 0,0:12:23.90,0:12:27.81,Default,,0000,0000,0000,,but certainly we can control the emissions rate for lead.
Dialogue: 0,0:12:27.81,0:12:35.01,Default,,0000,0000,0000,,So now let’s throw another curve ball into the problem.
Dialogue: 0,0:12:35.01,0:12:41.15,Default,,0000,0000,0000,,Let’s say that we now want to find out how long it would take
Dialogue: 0,0:12:41.15,0:12:44.87,Default,,0000,0000,0000,,to reduce our air pollution, our Cout,
Dialogue: 0,0:12:44.87,0:12:48.60,Default,,0000,0000,0000,,if we had a sudden change in emission rate or wind speed.
Dialogue: 0,0:12:48.60,0:12:53.67,Default,,0000,0000,0000,,Let’s say that again we, we found some mechanism to reduce the lead emissions.
Dialogue: 0,0:12:53.67,0:12:57.94,Default,,0000,0000,0000,,Well again now this, is this a steady state or a non-steady state problem?
Dialogue: 0,0:12:57.94,0:13:00.74,Default,,0000,0000,0000,,Steady state, raise your hands.
Dialogue: 0,0:13:00.74,0:13:05.27,Default,,0000,0000,0000,,Uh, no. You’re going to have problems in a couple weeks.
Dialogue: 0,0:13:05.27,0:13:10.40,Default,,0000,0000,0000,,We’re changing, we’re changing the temporal variable here.
Dialogue: 0,0:13:10.40,0:13:14.61,Default,,0000,0000,0000,,We’re looking at a change in time to see a change in, in concentration.
Dialogue: 0,0:13:14.61,0:13:18.00,Default,,0000,0000,0000,,So dmdt is not 0. That’s what we’re looking for.
Dialogue: 0,0:13:18.00,0:13:20.14,Default,,0000,0000,0000,,So we have to go into our, again you,
Dialogue: 0,0:13:20.14,0:13:23.67,Default,,0000,0000,0000,,you’d be given this solve solution for the differential equation.
Dialogue: 0,0:13:23.67,0:13:25.31,Default,,0000,0000,0000,,But the first thing when you hit these problems,
Dialogue: 0,0:13:25.31,0:13:28.27,Default,,0000,0000,0000,,you have to ask yourself is it steady state or not.
Dialogue: 0,0:13:28.27,0:13:31.00,Default,,0000,0000,0000,,So we’re looking at a change in concentration over time,
Dialogue: 0,0:13:31.00,0:13:33.67,Default,,0000,0000,0000,,so it’s going to be non-steady state.
Dialogue: 0,0:13:33.67,0:13:36.27,Default,,0000,0000,0000,,Conservative or non-conservative pollutant?
Dialogue: 0,0:13:36.27,0:13:39.94,Default,,0000,0000,0000,,Conservative?
Dialogue: 0,0:13:39.94,0:13:42.31,Default,,0000,0000,0000,,I know it’s the end of the day on Thursday.
Dialogue: 0,0:13:42.31,0:13:43.87,Default,,0000,0000,0000,,But this will wake you up.
Dialogue: 0,0:13:43.87,0:13:46.74,Default,,0000,0000,0000,,Conservative, yes it is a conservative pollutant.
Dialogue: 0,0:13:46.74,0:13:49.23,Default,,0000,0000,0000,,We haven’t changed anything with respect to lead.
Dialogue: 0,0:13:49.23,0:13:52.60,Default,,0000,0000,0000,,No reactions. Those conditions are the same.
Dialogue: 0,0:13:52.60,0:13:54.40,Default,,0000,0000,0000,,So again, when you look at these problems
Dialogue: 0,0:13:54.40,0:13:57.81,Default,,0000,0000,0000,,you’re going to have to ask yourself is this a steady state problem or not.
Dialogue: 0,0:13:57.81,0:14:02.23,Default,,0000,0000,0000,,Are we looking at a change, dcdt, or not?
Dialogue: 0,0:14:02.23,0:14:08.87,Default,,0000,0000,0000,,Okay. So that’s a way to solve our mass balance equations.
Dialogue: 0,0:14:08.87,0:14:11.54,Default,,0000,0000,0000,,Now we’re going to start talking a little bit about chemistry.
Dialogue: 0,0:14:11.54,0:14:16.67,Default,,0000,0000,0000,,So what is smog? And of course it comes from the term smoke and fog.
Dialogue: 0,0:14:16.67,0:14:21.87,Default,,0000,0000,0000,,In your readings, in that extra handout that you received,
Dialogue: 0,0:14:21.87,0:14:25.00,Default,,0000,0000,0000,,there’s an introduction to the reading that was in the course pack
Dialogue: 0,0:14:25.00,0:14:29.67,Default,,0000,0000,0000,,and it talked about air pollution episodes in London.
Dialogue: 0,0:14:29.67,0:14:33.40,Default,,0000,0000,0000,,And we talked about Donora in class a few, a few lectures ago.
Dialogue: 0,0:14:33.40,0:14:40.40,Default,,0000,0000,0000,,So in those cases, you had water droplets that had both sulfur dioxide
Dialogue: 0,0:14:40.40,0:14:43.48,Default,,0000,0000,0000,,and particulate matter in them,
Dialogue: 0,0:14:43.48,0:14:49.14,Default,,0000,0000,0000,,and that smog again was formed primarily from the particulate matter and smoke.
Dialogue: 0,0:14:49.14,0:14:57.40,Default,,0000,0000,0000,,And the SO2 that absorbed that can cause in particulate matter causes
Dialogue: 0,0:14:57.40,0:15:01.56,Default,,0000,0000,0000,,some serious health effects. Now that does not require any sunlight to form.
Dialogue: 0,0:15:01.56,0:15:07.67,Default,,0000,0000,0000,,That’s, that’s a straight physical phenomenon and the cause of smog
Dialogue: 0,0:15:07.67,0:15:14.23,Default,,0000,0000,0000,,that we have seen in urban environments and the cause of smog that we see in Beijing.
Dialogue: 0,0:15:14.23,0:15:18.48,Default,,0000,0000,0000,,So here’s some photos of some traditional smog scenarios.
Dialogue: 0,0:15:18.48,0:15:23.07,Default,,0000,0000,0000,,It can often occur in the winter when temperature inversions can trap pollutants
Dialogue: 0,0:15:23.07,0:15:27.81,Default,,0000,0000,0000,,and we form these water droplets with sulfur dioxide and particulate matter.
Dialogue: 0,0:15:27.81,0:15:30.23,Default,,0000,0000,0000,,Again, this does not require sunlight.
Dialogue: 0,0:15:30.23,0:15:33.56,Default,,0000,0000,0000,,So, and these are pretty, pretty gnarly conditions.
Dialogue: 0,0:15:33.56,0:15:39.74,Default,,0000,0000,0000,,I don’t know if you any of you’ve experienced these in a heavy urban environment,
Dialogue: 0,0:15:39.74,0:15:44.94,Default,,0000,0000,0000,,but they cause respiratory distress and, and other health effects.
Dialogue: 0,0:15:44.94,0:15:49.64,Default,,0000,0000,0000,,So now we’ll move into photochemical smog and
Dialogue: 0,0:15:49.64,0:15:54.54,Default,,0000,0000,0000,,the one that’s become a much larger issue of concern.
Dialogue: 0,0:15:54.54,0:15:59.34,Default,,0000,0000,0000,,So what can cause smog?
Dialogue: 0,0:15:59.34,0:16:05.23,Default,,0000,0000,0000,,Well again we have these fine particles that are discharged in power plants primarily.
Dialogue: 0,0:16:05.23,0:16:08.81,Default,,0000,0000,0000,,If we are using diesel fuels,
Dialogue: 0,0:16:08.81,0:16:14.07,Default,,0000,0000,0000,,those can also have particulate matter in their discharge pipes.
Dialogue: 0,0:16:14.07,0:16:20.23,Default,,0000,0000,0000,,So again, these fine particles can blend with the water dot,
Dialogue: 0,0:16:20.23,0:16:25.93,Default,,0000,0000,0000,,droplets in fog and cause this smog, which can be deposited.
Dialogue: 0,0:16:25.93,0:16:30.56,Default,,0000,0000,0000,,What we’re going to be looking at further will be photochemical smog,
Dialogue: 0,0:16:30.56,0:16:37.07,Default,,0000,0000,0000,,which is formed primarily due to NOx, meaning NO or NO2.
Dialogue: 0,0:16:37.07,0:16:42.14,Default,,0000,0000,0000,,I’ll use that as an abbreviation, but NOx, nitrogen oxides,
Dialogue: 0,0:16:42.14,0:16:48.48,Default,,0000,0000,0000,,that are discharged along with volatile organic compounds in a variety sources.
Dialogue: 0,0:16:48.48,0:16:53.06,Default,,0000,0000,0000,,Those are discharged from factories.
Dialogue: 0,0:16:53.06,0:16:56.56,Default,,0000,0000,0000,,You know if you have a boiler that is generating heat,
Dialogue: 0,0:16:56.56,0:17:02.00,Default,,0000,0000,0000,,that boiler will discharge NOx and some volatile organic compounds.
Dialogue: 0,0:17:02.00,0:17:06.31,Default,,0000,0000,0000,,Of course at a refinery or other chemical plant as a chemical process,
Dialogue: 0,0:17:06.31,0:17:11.56,Default,,0000,0000,0000,,you can have NOx and, and VOCs discharged.
Dialogue: 0,0:17:11.56,0:17:19.07,Default,,0000,0000,0000,,Vehicles will discharge NO as the primary pollutant and VOCs from the tailpipes.
Dialogue: 0,0:17:19.07,0:17:23.34,Default,,0000,0000,0000,,So you have a number of sources of NOx and VOCs that
Dialogue: 0,0:17:23.34,0:17:28.13,Default,,0000,0000,0000,,I’ll show you can form ozone in the troposphere.
Dialogue: 0,0:17:28.13,0:17:30.40,Default,,0000,0000,0000,,Again this is the bad ozone.
Dialogue: 0,0:17:30.40,0:17:33.98,Default,,0000,0000,0000,,You may recall that the stratospheric ozone,
Dialogue: 0,0:17:33.98,0:17:39.00,Default,,0000,0000,0000,,that ozone blocks some very powerful UV radiation and
Dialogue: 0,0:17:39.00,0:17:42.00,Default,,0000,0000,0000,,so we want to keep that ozone in the atmosphere.
Dialogue: 0,0:17:42.00,0:17:47.67,Default,,0000,0000,0000,,This, this ozone that we’re generating as you’ll see shortly has a number
Dialogue: 0,0:17:47.67,0:17:53.48,Default,,0000,0000,0000,,of health effects and other chemical effects that are, that are not good.
Dialogue: 0,0:17:53.48,0:17:55.40,Default,,0000,0000,0000,,So what’s photochemical smog?
Dialogue: 0,0:17:55.40,0:18:01.74,Default,,0000,0000,0000,,Well we generally have to look at the impact of volatile organic compounds and
Dialogue: 0,0:18:01.74,0:18:07.56,Default,,0000,0000,0000,,NOx in a photochemical reaction that’s going to generate smog.
Dialogue: 0,0:18:07.56,0:18:14.87,Default,,0000,0000,0000,,Now in this definition we’re calling smog essentially the photochemical oxidants primarily ozone.
Dialogue: 0,0:18:14.87,0:18:20.56,Default,,0000,0000,0000,,So this is in again the, these droplets that will contain sulfur dioxide
Dialogue: 0,0:18:20.56,0:18:25.56,Default,,0000,0000,0000,,and particulate matter, we’re talking primarily about production of ozone.
Dialogue: 0,0:18:25.56,0:18:28.23,Default,,0000,0000,0000,,One little number to keep in the back of your mind is that
Dialogue: 0,0:18:28.23,0:18:33.34,Default,,0000,0000,0000,,the National Ambient Air Quality Standard for ozone is 120 ppb,
Dialogue: 0,0:18:33.34,0:18:37.54,Default,,0000,0000,0000,,and so this is the trip for, for other activities.
Dialogue: 0,0:18:37.54,0:18:40.48,Default,,0000,0000,0000,,So what’s the big deal with ozone?
Dialogue: 0,0:18:40.48,0:18:43.20,Default,,0000,0000,0000,,Well it’s an irritant.
Dialogue: 0,0:18:43.20,0:18:48.06,Default,,0000,0000,0000,,Again, it’s an oxidant and so it can irritate your respiratory system.
Dialogue: 0,0:18:48.06,0:18:50.23,Default,,0000,0000,0000,,It can be an eye irritant.
Dialogue: 0,0:18:50.23,0:18:53.67,Default,,0000,0000,0000,,So it’s again something that you don’t want to be around,
Dialogue: 0,0:18:53.67,0:18:56.56,Default,,0000,0000,0000,,especially if you’re sensitive populations.
Dialogue: 0,0:18:56.56,0:18:59.27,Default,,0000,0000,0000,,But there are other effects according to, other effects that follow
Dialogue: 0,0:18:59.27,0:19:01.23,Default,,0000,0000,0000,,from higher ozone levels.
Dialogue: 0,0:19:01.23,0:19:05.15,Default,,0000,0000,0000,,Ozone actually causes 90% of the damage to agriculture.
Dialogue: 0,0:19:05.15,0:19:09.56,Default,,0000,0000,0000,,It can impact tree foliage and can stunt growth.
Dialogue: 0,0:19:09.56,0:19:13.81,Default,,0000,0000,0000,,Crop damage due to ozone may exceed $2 to $3 billion a year,
Dialogue: 0,0:19:13.81,0:19:18.98,Default,,0000,0000,0000,,which is again a significant part of our agricultural productivity, 2% to 3%.
Dialogue: 0,0:19:18.98,0:19:23.00,Default,,0000,0000,0000,,Now the benefit is that again a lot of these agricultural areas
Dialogue: 0,0:19:23.00,0:19:26.00,Default,,0000,0000,0000,,are outside of areas with significant ozone production,
Dialogue: 0,0:19:26.00,0:19:29.48,Default,,0000,0000,0000,,but ozone is transported in ambient air.
Dialogue: 0,0:19:29.48,0:19:33.98,Default,,0000,0000,0000,,So it, it has an impact on our, on our agriculture.
Dialogue: 0,0:19:33.98,0:19:39.23,Default,,0000,0000,0000,,Well tire life, I mean all of us drive vehicles,
Dialogue: 0,0:19:39.23,0:19:46.15,Default,,0000,0000,0000,,but tires breakdown these days not so much due to typical tread wear,
Dialogue: 0,0:19:46.15,0:19:50.40,Default,,0000,0000,0000,,but also by sidewalls deteriorating due to the presence of ozone.
Dialogue: 0,0:19:50.40,0:19:52.06,Default,,0000,0000,0000,,Again ozone is an oxidant.
Dialogue: 0,0:19:52.06,0:19:56.40,Default,,0000,0000,0000,,So it’s going to breakdown rubber and it will have an impact on your tires.
Dialogue: 0,0:19:56.40,0:20:00.67,Default,,0000,0000,0000,,So other evidence of smog damage include fading and cracking of paints
Dialogue: 0,0:20:00.67,0:20:03.90,Default,,0000,0000,0000,,and some accelerated metal corrosion.
Dialogue: 0,0:20:03.90,0:20:12.27,Default,,0000,0000,0000,,So we talked a bit about the chemicals that are responsible for smog production.
Dialogue: 0,0:20:12.27,0:20:23.27,Default,,0000,0000,0000,,When we combust air, you know we use air in to, for combustion,
Dialogue: 0,0:20:23.27,0:20:25.94,Default,,0000,0000,0000,,it’s a mix of primarily nitrogen and oxygen.
Dialogue: 0,0:20:25.94,0:20:31.56,Default,,0000,0000,0000,,Well that combustion will cause the formation of NO, which is our primary pollutant.
Dialogue: 0,0:20:31.56,0:20:39.40,Default,,0000,0000,0000,,But the NO can combine further with oxygen to cause NOx or NO2.
Dialogue: 0,0:20:39.40,0:20:46.94,Default,,0000,0000,0000,,So this NOx is what will react then with sunlight to, to form this oxygen atom.
Dialogue: 0,0:20:46.94,0:20:53.34,Default,,0000,0000,0000,,And this oxygen atom is highly reactive and that will combine with oxygen to form ozone.
Dialogue: 0,0:20:53.34,0:20:58.40,Default,,0000,0000,0000,,So our combustion doesn’t directly form ozone,
Dialogue: 0,0:20:58.40,0:21:06.67,Default,,0000,0000,0000,,but the combustion product, NOx, will again react with sunlight to form this oxygen atom,
Dialogue: 0,0:21:06.67,0:21:10.56,Default,,0000,0000,0000,,which will then combine with oxygen to form ozone.
Dialogue: 0,0:21:10.56,0:21:15.34,Default,,0000,0000,0000,,So ozone doesn’t keep building and building and building.
Dialogue: 0,0:21:15.34,0:21:19.94,Default,,0000,0000,0000,,Ozone is then degraded by NO.
Dialogue: 0,0:21:19.94,0:21:24.40,Default,,0000,0000,0000,,It will react with NO to form NO2 and oxygen.
Dialogue: 0,0:21:24.40,0:21:29.81,Default,,0000,0000,0000,,So you know the, the concentration of ozone in the troposphere
Dialogue: 0,0:21:29.81,0:21:35.54,Default,,0000,0000,0000,,is a balance between ozone production of course and ozone degradation.
Dialogue: 0,0:21:35.54,0:21:44.81,Default,,0000,0000,0000,,So looking at this in kind of a process model.
Dialogue: 0,0:21:44.81,0:21:51.56,Default,,0000,0000,0000,,We have emissions, again whether this comes from a boiler, from a power plant,
Dialogue: 0,0:21:51.56,0:22:02.00,Default,,0000,0000,0000,,from a vehicle, we’re going to produce NO, which will again form to NO2 formation,
Dialogue: 0,0:22:02.00,0:22:05.67,Default,,0000,0000,0000,,which can again cycle back to NO.
Dialogue: 0,0:22:05.67,0:22:12.80,Default,,0000,0000,0000,,That NO2 generates free oxygen, which will react with oxygen,
Dialogue: 0,0:22:12.80,0:22:17.20,Default,,0000,0000,0000,,molecular oxygen to form ozone. So this reaction does require sunlight.
Dialogue: 0,0:22:17.20,0:22:21.94,Default,,0000,0000,0000,,So you’ll see some temporal variation of course, in the production of ozone,
Dialogue: 0,0:22:21.94,0:22:27.81,Default,,0000,0000,0000,,you need sunlight to get this oxygen atom produced to form ozone.
Dialogue: 0,0:22:27.81,0:22:31.94,Default,,0000,0000,0000,,So you see again we have a balance.
Dialogue: 0,0:22:31.94,0:22:39.14,Default,,0000,0000,0000,,The nitrogen dioxide produces free oxygen, the oxygen atom which produces ozone,
Dialogue: 0,0:22:39.14,0:22:43.11,Default,,0000,0000,0000,,and yet we have NO that’s going to destroy ozone,
Dialogue: 0,0:22:43.11,0:22:47.87,Default,,0000,0000,0000,,and that balance is going to determine the ambient ozone level.
Dialogue: 0,0:22:47.87,0:22:52.60,Default,,0000,0000,0000,,So we if we look at equilibrium ozone concentrations
Dialogue: 0,0:22:52.60,0:22:56.98,Default,,0000,0000,0000,,as a function of the initial NOx concentration,
Dialogue: 0,0:22:56.98,0:23:03.64,Default,,0000,0000,0000,,everything is going to be dependent on the ratio of NO2 to NO.
Dialogue: 0,0:23:03.64,0:23:11.00,Default,,0000,0000,0000,,So we can calculate, we can use equilibrium concentrations to generate this,
Dialogue: 0,0:23:11.00,0:23:17.08,Default,,0000,0000,0000,,our ozone concentration as a function of these reaction rate constants,
Dialogue: 0,0:23:17.08,0:23:22.27,Default,,0000,0000,0000,,which will be dependent on sunlight, and our NO2 and NO concentrations.
Dialogue: 0,0:23:22.27,0:23:30.14,Default,,0000,0000,0000,,So if we look at the NO2 to NO ratio at .2, at a ratio of .2,
Dialogue: 0,0:23:30.14,0:23:35.06,Default,,0000,0000,0000,,that equilibrium ozone concentration will be pretty low.
Dialogue: 0,0:23:35.06,0:23:41.34,Default,,0000,0000,0000,,If we start, if we raise that ratio to .6,
Dialogue: 0,0:23:41.34,0:23:45.14,Default,,0000,0000,0000,,our equilibrium ozone concentration will still be low,
Dialogue: 0,0:23:45.14,0:23:48.40,Default,,0000,0000,0000,,but it will still be increasing of course.
Dialogue: 0,0:23:48.40,0:23:50.67,Default,,0000,0000,0000,,But as we get to a ratio of 1,
Dialogue: 0,0:23:50.67,0:23:54.74,Default,,0000,0000,0000,,then our equilibrium concentration starts to produce ozone
Dialogue: 0,0:23:54.74,0:24:04.44,Default,,0000,0000,0000,,and it’s greater than the rate that ozone is, is degraded.
Dialogue: 0,0:24:04.44,0:24:10.40,Default,,0000,0000,0000,,So this equilibrium ratio of NO2 to NO is the,
Dialogue: 0,0:24:10.40,0:24:13.65,Default,,0000,0000,0000,,you know the tripping factor that’ll drive whether
Dialogue: 0,0:24:13.65,0:24:18.90,Default,,0000,0000,0000,,we’re producing ozone or whether we’re degrading it.
Dialogue: 0,0:24:18.90,0:24:21.90,Default,,0000,0000,0000,,So how do VOCs fit in the mix?
Dialogue: 0,0:24:21.90,0:24:31.49,Default,,0000,0000,0000,,Well the VOCs don’t generate ozone directly.
Dialogue: 0,0:24:31.49,0:24:36.00,Default,,0000,0000,0000,,But again we can have production of this molecular,
Dialogue: 0,0:24:36.00,0:24:41.23,Default,,0000,0000,0000,,of this atomic oxygen with water to form these two hydroxyl radicals,
Dialogue: 0,0:24:41.23,0:24:44.81,Default,,0000,0000,0000,,and those hydroxyl radicals are very reactive.
Dialogue: 0,0:24:44.81,0:24:49.15,Default,,0000,0000,0000,,Those radicals will react with a hydrocarbon.
Dialogue: 0,0:24:49.15,0:24:53.48,Default,,0000,0000,0000,,In this case, you know we’re calling R, our hydrocarbon chain,
Dialogue: 0,0:24:53.48,0:24:58.27,Default,,0000,0000,0000,,this can be methane, ethane, you know a larger hydrocarbon chain.
Dialogue: 0,0:24:58.27,0:25:01.27,Default,,0000,0000,0000,,R is just going to be our symbol for those organics.
Dialogue: 0,0:25:01.27,0:25:07.23,Default,,0000,0000,0000,,So it will react with that hydroxyl radical and nitrous oxide and oxygen
Dialogue: 0,0:25:07.23,0:25:16.00,Default,,0000,0000,0000,,to form more of this NO2, as well as the reactive radical
Dialogue: 0,0:25:16.00,0:25:23.56,Default,,0000,0000,0000,,that will continue to form some NO2, and this is kind of an ongoing chain.
Dialogue: 0,0:25:23.56,0:25:27.40,Default,,0000,0000,0000,,So this, these hydrocarbons will generate these free radicals
Dialogue: 0,0:25:27.40,0:25:31.48,Default,,0000,0000,0000,,and kind of fuel the production of NO2.
Dialogue: 0,0:25:31.48,0:25:40.27,Default,,0000,0000,0000,,So what happens is we wind up essentially using up the NO that would typically
Dialogue: 0,0:25:40.27,0:25:45.00,Default,,0000,0000,0000,,be used to degrade the ozone, we’re going to form NO2,
Dialogue: 0,0:25:45.00,0:25:47.54,Default,,0000,0000,0000,,which will thereby form more ozone.
Dialogue: 0,0:25:47.54,0:25:52.60,Default,,0000,0000,0000,,So this is a kind of a, a positive feedback mechanism
Dialogue: 0,0:25:52.60,0:25:57.40,Default,,0000,0000,0000,,where we generate more ozone then is destroyed.
Dialogue: 0,0:25:57.40,0:26:02.07,Default,,0000,0000,0000,,So in Los Angeles we’ve got some geographic factors
Dialogue: 0,0:26:02.07,0:26:06.06,Default,,0000,0000,0000,,that can cause for these buildups of ozone.
Dialogue: 0,0:26:06.06,0:26:09.74,Default,,0000,0000,0000,,The first is we can have temperature inversions.
Dialogue: 0,0:26:09.74,0:26:14.60,Default,,0000,0000,0000,,So essentially our mixing height within the urban area is small.
Dialogue: 0,0:26:14.60,0:26:19.48,Default,,0000,0000,0000,,It essentially puts a lid on our airshed keeping the, essentially reducing
Dialogue: 0,0:26:19.48,0:26:25.23,Default,,0000,0000,0000,,that control volume, so increasing our concentration of ozone.
Dialogue: 0,0:26:25.23,0:26:31.74,Default,,0000,0000,0000,,If we have low wind speeds, again we’ll have fewer air exchanges
Dialogue: 0,0:26:31.74,0:26:37.56,Default,,0000,0000,0000,,and that will also increase the concentration of ozone within that control volume.
Dialogue: 0,0:26:37.56,0:26:42.90,Default,,0000,0000,0000,,Sunlight will drive production of this atomic oxygen,
Dialogue: 0,0:26:42.90,0:26:48.34,Default,,0000,0000,0000,,which will again react with molecular oxygen to form ozone.
Dialogue: 0,0:26:48.34,0:26:53.48,Default,,0000,0000,0000,,And vehicles will produce NO and then NO2, and of course VOCs
Dialogue: 0,0:26:53.48,0:27:01.40,Default,,0000,0000,0000,,that will fuel this free radical production to generate more NO2.
Dialogue: 0,0:27:01.40,0:27:08.94,Default,,0000,0000,0000,,So if we look at the buildup of NO, NO2, and ozone in L.A.,
Dialogue: 0,0:27:08.94,0:27:17.74,Default,,0000,0000,0000,,this is a fairly typical sort of production curve of nitrogen dioxide and,
Dialogue: 0,0:27:17.74,0:27:20.82,Default,,0000,0000,0000,,and nitric oxide in the atmosphere.
Dialogue: 0,0:27:20.82,0:27:26.67,Default,,0000,0000,0000,,Remember that 122 ppb is our maximum daily one-hour average.
Dialogue: 0,0:27:26.67,0:27:32.50,Default,,0000,0000,0000,,So this would be sort of the cut-off for the National Air Ambient Quality Standard.
Dialogue: 0,0:27:32.50,0:27:35.07,Default,,0000,0000,0000,,So typically we can hit that or come close to hitting
Dialogue: 0,0:27:35.07,0:27:37.87,Default,,0000,0000,0000,,that in L.A. in the late morning.
Dialogue: 0,0:27:37.87,0:27:39.74,Default,,0000,0000,0000,,You know we’ve got commuter traffic.
Dialogue: 0,0:27:39.74,0:27:41.84,Default,,0000,0000,0000,,We’re generating a lot of VOCs.
Dialogue: 0,0:27:41.84,0:27:44.67,Default,,0000,0000,0000,,These reactions occur fairly quickly,
Dialogue: 0,0:27:44.67,0:27:48.94,Default,,0000,0000,0000,,so we’ll get an increase production of, of NO2
Dialogue: 0,0:27:48.94,0:27:52.81,Default,,0000,0000,0000,,because of the emissions out of the tailpipe,
Dialogue: 0,0:27:52.81,0:27:57.27,Default,,0000,0000,0000,,as well as the hydroxyl radical formations
Dialogue: 0,0:27:57.27,0:28:00.48,Default,,0000,0000,0000,,from the hydrocarbons that are discharged to get a peak
Dialogue: 0,0:28:00.48,0:28:04.60,Default,,0000,0000,0000,,of ozone formation in the late morning.
Dialogue: 0,0:28:04.60,0:28:08.56,Default,,0000,0000,0000,,If you look in your readings that are some additional figures
Dialogue: 0,0:28:08.56,0:28:13.31,Default,,0000,0000,0000,,that show ozone concentration profiles over time.
Dialogue: 0,0:28:13.31,0:28:16.34,Default,,0000,0000,0000,,There was a figure in the reading from Massachusetts
Dialogue: 0,0:28:16.34,0:28:20.34,Default,,0000,0000,0000,,that showed this sort of morning peak due to commuting and
Dialogue: 0,0:28:20.34,0:28:28.40,Default,,0000,0000,0000,,then a later afternoon/early evening peak because of transportation of,
Dialogue: 0,0:28:28.40,0:28:34.54,Default,,0000,0000,0000,,or migration of ozone into that urban airshed at a later time
Dialogue: 0,0:28:34.54,0:28:37.20,Default,,0000,0000,0000,,from another up gradient site.
Dialogue: 0,0:28:37.20,0:28:41.48,Default,,0000,0000,0000,,So ozone in the local atmosphere will be dependent
Dialogue: 0,0:28:41.48,0:28:48.40,Default,,0000,0000,0000,,not only on the sunlight and wind speeds and temperatures
Dialogue: 0,0:28:48.40,0:28:51.14,Default,,0000,0000,0000,,and that big urban commute in the morning,
Dialogue: 0,0:28:51.14,0:28:55.20,Default,,0000,0000,0000,,but you can also have ozone then transported into your urban airshed. Go ahead.
Dialogue: 0,0:28:55.20,0:29:01.64,Default,,0000,0000,0000,,[Student Inaudible]
Dialogue: 0,0:29:01.64,0:29:04.90,Default,,0000,0000,0000,,Probably because the sunlight goes down.
Dialogue: 0,0:29:04.90,0:29:07.94,Default,,0000,0000,0000,,We don’t have as intense of radiation at that time,
Dialogue: 0,0:29:07.94,0:29:12.17,Default,,0000,0000,0000,,which again drives the formation of, of the NO2 and those radicals.
Dialogue: 0,0:29:12.17,0:29:17.07,Default,,0000,0000,0000,,So it’s fairly typical to see this curve drop off later in the day,
Dialogue: 0,0:29:17.07,0:29:20.56,Default,,0000,0000,0000,,because just the sunlight isn’t strong.
Dialogue: 0,0:29:20.56,0:29:27.40,Default,,0000,0000,0000,,Well here’s some photographs of Santiago, Chile.
Dialogue: 0,0:29:27.40,0:29:33.74,Default,,0000,0000,0000,,Fairly similar scenario with L.A. in that you’ve got an urban population in a valley,
Dialogue: 0,0:29:33.74,0:29:38.48,Default,,0000,0000,0000,,and so late morning things are actually not looking too bad,
Dialogue: 0,0:29:38.48,0:29:43.54,Default,,0000,0000,0000,,but by late afternoon with the buildup of vehicle traffic and the sunlight,
Dialogue: 0,0:29:43.54,0:29:49.34,Default,,0000,0000,0000,,we’ve got smog formation that really impacts visibility.
Dialogue: 0,0:29:49.34,0:29:55.90,Default,,0000,0000,0000,,Okay. So we have talked a bit about our box model for urban ozone formation.
Dialogue: 0,0:29:55.90,0:29:59.73,Default,,0000,0000,0000,,Again, the, the parameters to remember that are important
Dialogue: 0,0:29:59.73,0:30:04.00,Default,,0000,0000,0000,,will be the wind velocity, the emission rate, the deposition velocity,
Dialogue: 0,0:30:04.00,0:30:08.56,Default,,0000,0000,0000,,and of course the geometry that you need to set up your control volume.
Dialogue: 0,0:30:08.56,0:30:13.48,Default,,0000,0000,0000,,So you know and we, we can set up these mass balance equations,
Dialogue: 0,0:30:13.48,0:30:17.34,Default,,0000,0000,0000,,that emission rate is going to be a really important number.
Dialogue: 0,0:30:17.34,0:30:20.27,Default,,0000,0000,0000,,Our deposition rate, which is often quite unknown,
Dialogue: 0,0:30:20.27,0:30:22.00,Default,,0000,0000,0000,,is going to be an important number,
Dialogue: 0,0:30:22.00,0:30:25.74,Default,,0000,0000,0000,,and again whether we have any reaction of the material.
Dialogue: 0,0:30:25.74,0:30:34.40,Default,,0000,0000,0000,,Now we can look at box models for ozone including VOCs inputs
Dialogue: 0,0:30:34.40,0:30:37.48,Default,,0000,0000,0000,,and NOx inputs and that’s of course well beyond the,
Dialogue: 0,0:30:37.48,0:30:41.56,Default,,0000,0000,0000,,the scope of this course, but we can come up with models
Dialogue: 0,0:30:41.56,0:30:47.94,Default,,0000,0000,0000,,that will predict ozone formation based on an initial VOC concentration.
Dialogue: 0,0:30:47.94,0:30:53.20,Default,,0000,0000,0000,,So remember when VOC levels are high there’s,
Dialogue: 0,0:30:53.20,0:30:58.00,Default,,0000,0000,0000,,there’s still plenty to convert NO to NO2.
Dialogue: 0,0:30:58.00,0:31:04.36,Default,,0000,0000,0000,,But we have to remember that, that NO destroys ozone, but NO2 creates it.
Dialogue: 0,0:31:04.36,0:31:09.00,Default,,0000,0000,0000,,So this graph just looks at total carbon in an atmosphere and
Dialogue: 0,0:31:09.00,0:31:15.90,Default,,0000,0000,0000,,we certainly see the increase of ozone production with an increase in VOCs.
Dialogue: 0,0:31:15.90,0:31:19.00,Default,,0000,0000,0000,,Now looking at the magnitude of these things,
Dialogue: 0,0:31:19.00,0:31:23.90,Default,,0000,0000,0000,,you know when you’re already out in the kind of plateau area of this curve,
Dialogue: 0,0:31:23.90,0:31:26.98,Default,,0000,0000,0000,,you can look that you know if you reduce VOCs by 20%,
Dialogue: 0,0:31:26.98,0:31:31.54,Default,,0000,0000,0000,,you’re just not going to have much of an impact on ozone production.
Dialogue: 0,0:31:31.54,0:31:36.23,Default,,0000,0000,0000,,You’re really in an insensitive part of the model to VOC production.
Dialogue: 0,0:31:36.23,0:31:41.00,Default,,0000,0000,0000,,You’ve really got to get down to some much lower concentrations of VOCs.
Dialogue: 0,0:31:41.00,0:31:44.67,Default,,0000,0000,0000,,In this case, you know we went from an 80% reduction in VOCs
Dialogue: 0,0:31:44.67,0:31:49.48,Default,,0000,0000,0000,,and that had a 30% impact on ozone production.
Dialogue: 0,0:31:49.48,0:31:53.07,Default,,0000,0000,0000,,So again these models are, are dependent on VOCs,
Dialogue: 0,0:31:53.07,0:31:55.48,Default,,0000,0000,0000,,but once we get out into these plateau areas
Dialogue: 0,0:31:55.48,0:32:00.23,Default,,0000,0000,0000,,it’s going to be fairly insensitive to any reductions in VOCs.
Dialogue: 0,0:32:00.23,0:32:08.14,Default,,0000,0000,0000,,So we look at ozone creation as a function of the NOx concentration.
Dialogue: 0,0:32:08.14,0:32:15.77,Default,,0000,0000,0000,,We have our initial NOx concentrations and our ozone production actually peaks,
Dialogue: 0,0:32:15.77,0:32:21.87,Default,,0000,0000,0000,,and then it starts to drop off. So why does that happen?
Dialogue: 0,0:32:21.87,0:32:25.67,Default,,0000,0000,0000,,I mean you would think intuitively well if I decrease NOx
Dialogue: 0,0:32:25.67,0:32:27.81,Default,,0000,0000,0000,,then I should decrease ozone.
Dialogue: 0,0:32:27.81,0:32:35.67,Default,,0000,0000,0000,,But remember that when we produce NO2 we’ll also produce some NO at some point
Dialogue: 0,0:32:35.67,0:32:40.31,Default,,0000,0000,0000,,and so as we start to produce NO, that’s going to destroy ozone
Dialogue: 0,0:32:40.31,0:32:45.60,Default,,0000,0000,0000,,and it’s going to decrease the ozone concentrations in our model.
Dialogue: 0,0:32:45.60,0:32:50.27,Default,,0000,0000,0000,,So in this case, if our ozone, if our NOx concentrations are high,
Dialogue: 0,0:32:50.27,0:32:53.34,Default,,0000,0000,0000,,let’s say in that 122 ppb range,
Dialogue: 0,0:32:53.34,0:32:57.34,Default,,0000,0000,0000,,you may think well let’s reduce NOx to reduce our ozone,
Dialogue: 0,0:32:57.34,0:32:59.94,Default,,0000,0000,0000,,but actually according to that equilibrium model,
Dialogue: 0,0:32:59.94,0:33:04.81,Default,,0000,0000,0000,,we’ll actually increase the ozone concentrations because we aren’t producing as much NO,
Dialogue: 0,0:33:04.81,0:33:09.10,Default,,0000,0000,0000,,which degrades the ozone.
Dialogue: 0,0:33:09.10,0:33:11.40,Default,,0000,0000,0000,,So you’ve really got see where you are in the model.
Dialogue: 0,0:33:11.40,0:33:15.27,Default,,0000,0000,0000,,You can’t automatically assume that okay I’m going to reduce VOC concentrations,
Dialogue: 0,0:33:15.27,0:33:19.81,Default,,0000,0000,0000,,I’ll get an ozone reduction, or I’m going to reduce NOx concentrations,
Dialogue: 0,0:33:19.81,0:33:21.90,Default,,0000,0000,0000,,I’ll get an ozone reduction.
Dialogue: 0,0:33:21.90,0:33:27.53,Default,,0000,0000,0000,,It really depends on the actual concentrations and where you are in the model.
Dialogue: 0,0:33:27.53,0:33:36.81,Default,,0000,0000,0000,,Okay. We’re going to look, kind of finish up our lecture today
Dialogue: 0,0:33:36.81,0:33:39.56,Default,,0000,0000,0000,,looking at some isopleth diagrams.
Dialogue: 0,0:33:39.56,0:33:45.34,Default,,0000,0000,0000,,It really can provide a roadmap as to how to deal with elevated ozone concentrations.
Dialogue: 0,0:33:45.34,0:33:53.54,Default,,0000,0000,0000,,So we can use these models to essentially come up with a contour map for ozone.
Dialogue: 0,0:33:53.54,0:33:55.23,Default,,0000,0000,0000,,This is really what this is.
Dialogue: 0,0:33:55.23,0:34:01.74,Default,,0000,0000,0000,,So we’ve plotted the ozone concentrations as a function of VOCs and NOx.
Dialogue: 0,0:34:01.74,0:34:09.07,Default,,0000,0000,0000,,So of course as you know we go and increase VOCs and increase NOx concentrations,
Dialogue: 0,0:34:09.07,0:34:15.23,Default,,0000,0000,0000,,our, essentially our isocontour lines for ozone concentrations here will increase.
Dialogue: 0,0:34:15.23,0:34:19.17,Default,,0000,0000,0000,,So using those model calculations for, you can,
Dialogue: 0,0:34:19.17,0:34:25.00,Default,,0000,0000,0000,,if you have a given concentration of VOC and a given concentration of NOx,
Dialogue: 0,0:34:25.00,0:34:30.00,Default,,0000,0000,0000,,you can predict your result in ozone concentration to see where you are on this map.
Dialogue: 0,0:34:30.00,0:34:37.67,Default,,0000,0000,0000,,So if you for example at .6 ppm of VOCs and about 120 ppb of NOx,
Dialogue: 0,0:34:37.67,0:34:44.48,Default,,0000,0000,0000,,you’d expect an ozone concentration of 240 ppb.
Dialogue: 0,0:34:44.48,0:34:54.27,Default,,0000,0000,0000,,So the, so any, any questions about what we’re looking at on these isopleth figures?
Dialogue: 0,0:34:54.27,0:34:57.27,Default,,0000,0000,0000,,So essentially we’re using our equilibrium model.
Dialogue: 0,0:34:57.27,0:35:01.56,Default,,0000,0000,0000,,We’re inputting a given concentration for VOCs, a given concentration for NOx,
Dialogue: 0,0:35:01.56,0:35:07.98,Default,,0000,0000,0000,,and it’s going to tell us really where we are in terms of the ozone concentration.
Dialogue: 0,0:35:07.98,0:35:16.07,Default,,0000,0000,0000,,So we can use these models to try to decide what we’re going to do if,
Dialogue: 0,0:35:16.07,0:35:21.40,Default,,0000,0000,0000,,you know how to address a given ozone concentration.
Dialogue: 0,0:35:21.40,0:35:25.23,Default,,0000,0000,0000,,So in this model we’ve identified what’s called a ridge line and
Dialogue: 0,0:35:25.23,0:35:34.31,Default,,0000,0000,0000,,it really divides where we are in ozone concentrations with respect to NOx versus VOCs.
Dialogue: 0,0:35:34.31,0:35:38.60,Default,,0000,0000,0000,,So if we are looking at this part of these isopleth diagrams,
Dialogue: 0,0:35:38.60,0:35:41.27,Default,,0000,0000,0000,,we’re essentially NOx limited,
Dialogue: 0,0:35:41.27,0:35:46.67,Default,,0000,0000,0000,,which means that the ozone production is really driven by the NOx concentration.
Dialogue: 0,0:35:46.67,0:35:53.48,Default,,0000,0000,0000,,We can vary VOCs all we want, but we’re not going to impact the VOC concentration at all.
Dialogue: 0,0:35:53.48,0:35:59.27,Default,,0000,0000,0000,,Similarly, where in this part of the isopleth diagram, we’re in a VOC limited regime.
Dialogue: 0,0:35:59.27,0:36:03.94,Default,,0000,0000,0000,,So we can change the NOX concentration really all we want,
Dialogue: 0,0:36:03.94,0:36:10.40,Default,,0000,0000,0000,,but, we can kind of go up and down the NOx curve, the NOx concentration,
Dialogue: 0,0:36:10.40,0:36:13.76,Default,,0000,0000,0000,,but we’re not going to change the ozone concentration very much.
Dialogue: 0,0:36:13.76,0:36:18.31,Default,,0000,0000,0000,,We again this is based on the interplay between VOCs and NOx
Dialogue: 0,0:36:18.31,0:36:21.14,Default,,0000,0000,0000,,and their associated rate constants.
Dialogue: 0,0:36:21.14,0:36:24.47,Default,,0000,0000,0000,,Now we’ve got a couple of different ways
Dialogue: 0,0:36:24.47,0:36:29.40,Default,,0000,0000,0000,,to look at ozone concentrations based on, on VOCs.
Dialogue: 0,0:36:29.40,0:36:33.27,Default,,0000,0000,0000,,One method is to use a carbon mass approach.
Dialogue: 0,0:36:33.27,0:36:39.31,Default,,0000,0000,0000,,So for example here, we’re looking at all VOCs essentially as if they were equal.
Dialogue: 0,0:36:39.31,0:36:46.34,Default,,0000,0000,0000,,So compounds with larger masses would have a larger impact on the ozone production.
Dialogue: 0,0:36:46.34,0:36:49.67,Default,,0000,0000,0000,,And, and that’s not a particularly accurate model.
Dialogue: 0,0:36:49.67,0:36:54.34,Default,,0000,0000,0000,,We have another model where we can look at reactive organic gases.
Dialogue: 0,0:36:54.34,0:36:57.23,Default,,0000,0000,0000,,So rather than looking at VOCs as a bulk,
Dialogue: 0,0:36:57.23,0:36:59.74,Default,,0000,0000,0000,,we can look at specific reactive gases and that’s a,
Dialogue: 0,0:36:59.74,0:37:01.81,Default,,0000,0000,0000,,that’s a little more accurate model.
Dialogue: 0,0:37:01.81,0:37:05.67,Default,,0000,0000,0000,,We can look at overall chemical reactivity and
Dialogue: 0,0:37:05.67,0:37:07.81,Default,,0000,0000,0000,,I’ll show you a table that looks at that,
Dialogue: 0,0:37:07.81,0:37:10.60,Default,,0000,0000,0000,,and that’s again a pretty good representation.
Dialogue: 0,0:37:10.60,0:37:16.20,Default,,0000,0000,0000,,But the best methodology that’s out there now looks at maximum incremental reactivity,
Dialogue: 0,0:37:16.20,0:37:20.00,Default,,0000,0000,0000,,and what that, what this ratio is,
Dialogue: 0,0:37:20.00,0:37:27.48,Default,,0000,0000,0000,,is really looks at the amount of ozone produced for a given change in VOC concentrations.
Dialogue: 0,0:37:27.48,0:37:31.14,Default,,0000,0000,0000,,Not all VOCs are created like, alike.
Dialogue: 0,0:37:31.14,0:37:35.56,Default,,0000,0000,0000,,Some will be responsible for a greater ozone production than others,
Dialogue: 0,0:37:35.56,0:37:38.87,Default,,0000,0000,0000,,and so the, we have an opportunity to look at that
Dialogue: 0,0:37:38.87,0:37:43.34,Default,,0000,0000,0000,,through this maximum incremental reactivity value.
Dialogue: 0,0:37:43.34,0:37:49.27,Default,,0000,0000,0000,,The California Air Quality Board essentially uses these values
Dialogue: 0,0:37:49.27,0:37:52.07,Default,,0000,0000,0000,,to look at emissions of specific VOCs.
Dialogue: 0,0:37:52.07,0:37:55.10,Default,,0000,0000,0000,,So again not all VOCs are, are alike.
Dialogue: 0,0:37:55.10,0:37:58.81,Default,,0000,0000,0000,,So by using these, these maximum incremental reactivity numbers
Dialogue: 0,0:37:58.81,0:38:05.65,Default,,0000,0000,0000,,we can get a much more accurate feel for ozone production for a given VOC emission.
Dialogue: 0,0:38:05.65,0:38:08.98,Default,,0000,0000,0000,,Any questions about these approaches?
Dialogue: 0,0:38:08.98,0:38:12.94,Default,,0000,0000,0000,,Okay. So again there were some problems in your reading
Dialogue: 0,0:38:12.94,0:38:20.40,Default,,0000,0000,0000,,that you should take a look at because you were given a set of VOC, NOx,
Dialogue: 0,0:38:20.40,0:38:23.87,Default,,0000,0000,0000,,and ozone concentrations and you have to decide really
Dialogue: 0,0:38:23.87,0:38:28.00,Default,,0000,0000,0000,,where you were on the curve and whether changing the NOx or
Dialogue: 0,0:38:28.00,0:38:31.31,Default,,0000,0000,0000,,changing the VOCs would have an impact on ozone.
Dialogue: 0,0:38:31.31,0:38:38.23,Default,,0000,0000,0000,,So hint-hint for the exam, make sure you understand how to use these diagrams.
Dialogue: 0,0:38:38.23,0:38:39.74,Default,,0000,0000,0000,,All right.
Dialogue: 0,0:38:39.74,0:38:44.40,Default,,0000,0000,0000,,This is a table that looks at a whole series of VOCs
Dialogue: 0,0:38:44.40,0:38:48.27,Default,,0000,0000,0000,,and compares reactivity constants.
Dialogue: 0,0:38:48.27,0:38:53.48,Default,,0000,0000,0000,,In other words, what kind of hydroxyl radical production rate could we have
Dialogue: 0,0:38:53.48,0:38:57.82,Default,,0000,0000,0000,,versus this maximum incremental reactivity number,
Dialogue: 0,0:38:57.82,0:39:02.81,Default,,0000,0000,0000,,which is again a ratio of ozone formed per, per gram of VOC emitted.
Dialogue: 0,0:39:02.81,0:39:09.48,Default,,0000,0000,0000,,And the interesting thing about this table is that these data don’t always match up.
Dialogue: 0,0:39:09.48,0:39:14.16,Default,,0000,0000,0000,,So the hydroxyl radical formation isn’t necessarily parallel
Dialogue: 0,0:39:14.16,0:39:18.36,Default,,0000,0000,0000,,to the maximum incremental reactivity.
Dialogue: 0,0:39:18.36,0:39:23.64,Default,,0000,0000,0000,,Now the numbers that we’re most concerned about with the MIR
Dialogue: 0,0:39:23.64,0:39:27.31,Default,,0000,0000,0000,,are values that are generally 5 and above.
Dialogue: 0,0:39:27.31,0:39:35.48,Default,,0000,0000,0000,,So if we have compounds like ethane, n-octane, propene, trimethyl benzene,
Dialogue: 0,0:39:35.48,0:39:38.34,Default,,0000,0000,0000,,you know those are going to be responsible
Dialogue: 0,0:39:38.34,0:39:43.17,Default,,0000,0000,0000,,for more significant ozone production than compounds like methane or, or.
Dialogue: 0,0:39:43.17,0:39:43.47,Default,,0000,0000,0000,,