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See how confident you are with the Wolverines.

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Okay. So we’ve talked about urban air pollution

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a couple of times through this semester

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and this is actually a photograph of a typical day in Beijing.

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We saw the one a couple of lectures ago

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when someone was trying to raise a flag in Tiananmen Square and I,

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I couldn’t see the flag.

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But you know following a rainfall,

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Beijing can clear up and so what we’re going to talk about today

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are some of the causes of urban air pollution,

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specifically around smog and photochemical smog.

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So what we’ll talk about today again will be

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some of the primary pollutants of concern.

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Criteria air pollutants as we call them

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in the regulatory framework of the U.S. CPA.

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We’re going to be able to do calculations using

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mass balance equations just like we did earlier,

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whether it was for a, you know earlier we looked at lakes and creeks merging.

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We looked at reactors.

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We’re going to look at an urban box model for air pollution

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and we’ll do similar sorts of calculations

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looking at pollutants in and out,

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and those that can be generated within that volume.

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We’ll talk a bit about the mechanisms of photochemical smog formation.

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You may remember a couple of lectures ago

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we talked about good ozone and bad ozone,

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and the focus today will be on the bad ozone,

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the ozone in the troposphere.

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We’ll finish up with some discussion of isopleth diagrams

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and ozone forming potential, and that will give you

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an idea of perhaps some management tools

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for looking at reducing NOx or VOCs and formation of photochemical smog.

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And we’ll talk about a nice little calculation tool at the end of the lecture,

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the MIR, the maximum incremental reactivity scale.

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It gives us a way to look at some individual VOCs and their potential for ozone formation.

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Okay so we have talked about the primary air contaminants

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of concern in urban environments and criteria air pollutants.

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So you may remember this figure.

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So we talked about sources of air pollution.

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Of course, coal burning power plants, ones that are very prevalent in China,

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are responsible for emitting SOx and NOx and particulates and hydrocarbons,

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and those are all criteria air pollutants.

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Urban transportation, motor vehicles are also significant sources of admissions

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of both NOx and hydrocarbons, particularly carbon monoxide

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and other partially burned fuels.

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Incinerators, other industrial stacks, can be sources of air pollution as well.

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So there are a number of sources to consider.

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When we do some of our box model monitor, modeling,

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of course we’re going to be looking at things at a fairly large scale.

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But as you reduce your scale,

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if you become the environmental engineer at an industrial facility,

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and someone tells you we’re going to put another stack out the roof

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because we’re going to add a new process,

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well then you have to look at the impact of that stack and

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its emissions on the ambient air.

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Are you going to be increasing NOx?

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Are you going to be increasing VOCs at the property boundary?

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So we talked earlier about the major criteria air pollutants,

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carbon monoxide and O2 ozone, SO2, lead, and particulate matter.

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The focus today will be a lot on NO2,

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which is responsible for photochemical smog, the resultant pollutant ozone,

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and other VOCs that are CAPs.

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Another term you may hear in the air pollution vernacular

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is HAPs or hazardous air pollutants.

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These are typically going to be VOCs like benzene or aldehydes,

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other, other volatile organic compounds, heavy metals,

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and other pollutants that are emitted at much smaller doses.

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But typically an air permitting authority would look at

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the total sum of all the HAPs in that emission rather than individual HAPs.

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So we have, we’ll start with a, a mass balance problem,

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much like we did earlier in, in looking at water.

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So we have a city with a given area that has a daily lead emission rate of 5,000 kg/d.

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Typically, those would be from auto exhaust and other industrial processes.

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Background concentrations of lead we’re going to be given at .1 mcg/m3.

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Now during a hot summer day we have a mixing height of 500 meters

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and a wind speed of 2 m/s.

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So you’ll see when we set up the box model those are variables

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that we need to look at a mass balance and a flow of air

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through a given control volume.

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So we have emissions of lead at 5,000 kg/d,

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but we also have lead deposition from the atmosphere at .05 cm/s.

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So our question is what is the steady state lead concentration in the urban air?

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So remember when we started to talk about mass balance equations,

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you have to get into your mind the thought that

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is this steady state or non-steady state?

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Is this a conservative pollutant or a non-conservative pollutant?

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So with the information we have here,

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everybody raise your hand who thinks this is a steady state problem?

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Please more hands or else you’re going to have a rough time in two weeks.

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Okay. This is a definite, we’re asking what’s the steady state lead concentration.

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Second question, is this is a conservative or a non-conservative pollutant?

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Conservative, raise your hands.

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Okay. This, this is a conservative pollutant.

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We’re not transforming lead.

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We’re not degrading lead.

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Now it, it’s going to be emitted and it’s going to be deposited,

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and that’s going to be part of our mass balance equation,

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but we’re not going to be changing the form of lead in the, in the problem.

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Okay, so this is our box model.

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And we we’re given the area of Leadville,

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so those will be inputs into our calculations.

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We set up an atmospheric mixing height that was given in the problem as 500 meters.

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So we have our control volume for the air pollution problem.

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It’s going to be the area of the city times the mixing height of the problem.

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So we have our control volume.

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We will have a wind velocity going in and out of that control volume.

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We were given a pollutant emission rate M,

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that was for lead in kilograms per day.

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We also have a pollutant deposition velocity Vd.

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So those are the, the parameters around the control volume.

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So as we did before, we can set up a mass balance equation

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looking at the change of mass over time being equal to the mass in minus the mass out,

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plus whatever mass is reacted.

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So we said this was a steady state problem,

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so the dm/dt is going to be equal to 0.

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Lead is not going to be transformed in this problem.

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We’re not, it’s not going to be reduced or oxidized.

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It’s, it’s not changing any, any forms,

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so we’ll have masses going in and out as part of the mass balance,

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but no reaction of lead.

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So the first thing we can do is a mass balance on the air.

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If you remember when we did these water problems,

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the first thing we did was look at the mass balance on the water,

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and the mass balance on the air is going to be pretty straightforward.

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It’s going to be the flow times the density of air.

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The mass of air going out is going to be the flow out times the density of air going out,

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and we can set these equal to each other.

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We know mass in is going to equal mass out and we can substitute a term,

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rather than the flow times the density we can use the,

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the velocity times the, times the cross-sectional area.

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Okay, so our next step is to look at the mass balance on the pollutant.

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So again, looking at this mass balance model,

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again our flow in is going to be flow out.

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So we’ve, we’ve settled that.

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So our mass going into our control volume is going to be

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the flow times the concentration coming in plus M, our mass emissions rate.

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So we have lead in the background that’s coming into our control volume

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and we have a lead emission rate within that control volume.

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Our mass leaving that control volume will be the flow times

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the concentration going out at that border plus the depositional velocity times

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the cross-sectional area of that city times the concentration.

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So again, we said this was going to be a steady state problem,

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so mass in is going to equal mass out.

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So we can substitute a few terms.

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Rather than Q we can use the cross-sectional velocity or

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the wind velocity times the cross-sectional area of the Leadville,

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substituting that for Q and so again we set up terms mass in,

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concentration plus the emission rate, mass out,

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flow times concentration out plus the depositional rate.

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So again, lead is not being transformed.

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It’s either physically coming in or out of the system.

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Okay, so we can set up our mass balance equation

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for the pollutant that the mass in is going to be the mass out.

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We can rearrange terms and solve for concentration out.

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We didn’t carry all the units,

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but at home make sure that you double check that you carry the units through

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and that they’ve been cancelled out properly.

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And we get a concentration out at .55 mcg/m3.

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Okay, so very similar to the problems we solved before.

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Steady state conservative pollutant so we can set the mass in equal to the mass out.

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The only thing that’s a little different here is

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you have to make sure you understand how we set up the control volume

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and that we are given a mass emission rate and lead deposition rate.

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So those are again in and out of the system.

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Okay, any questions on setting up a mass balance for air?

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It’s a control volume like anything else.

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We just have to make sure that when you do these calculations

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that you carry the units properly.

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You may be given units to convert in an exam problem.

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So you have to understand how to do that. Okay.

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So we if we look at the way our, our mass balance equation

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is set up in terms of Cout, the question is how can we lower that Cout?

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You know if we want to reduce lead emissions there are a couple obvious answers.

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I mean we certainly can reduce the mass emissions rate.

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You know if we reduce M, then Cout is going to be reduced.

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The other opportunity here is if we have a very low, low background.

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If we increase Z, the mixing height or the wind velocity,

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it will also reduce the concentration going out.

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So you know we don’t have control over these issues,

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but certainly we can control the emissions rate for lead.

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So now let’s throw another curve ball into the problem.

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Let’s say that we now want to find out how long it would take

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to reduce our air pollution, our Cout,

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if we had a sudden change in emission rate or wind speed.

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Let’s say that again we, we found some mechanism to reduce the lead emissions.

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Well again now this, is this a steady state or a non-steady state problem?

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Steady state, raise your hands.

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Uh, no. You’re going to have problems in a couple weeks.

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We’re changing, we’re changing the temporal variable here.

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We’re looking at a change in time to see a change in, in concentration.

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So dmdt is not 0. That’s what we’re looking for.

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So we have to go into our, again you,

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you’d be given this solve solution for the differential equation.

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But the first thing when you hit these problems,

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you have to ask yourself is it steady state or not.

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So we’re looking at a change in concentration over time,

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so it’s going to be non-steady state.

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Conservative or non-conservative pollutant?

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Conservative?

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I know it’s the end of the day on Thursday.

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But this will wake you up.

202
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Conservative, yes it is a conservative pollutant.

203
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We haven’t changed anything with respect to lead.

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No reactions. Those conditions are the same.

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So again, when you look at these problems

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you’re going to have to ask yourself is this a steady state problem or not.

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Are we looking at a change, dcdt, or not?

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00:14:02,230 --> 00:14:08,869
Okay. So that’s a way to solve our mass balance equations.

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Now we’re going to start talking a little bit about chemistry.

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So what is smog? And of course it comes from the term smoke and fog.

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In your readings, in that extra handout that you received,

212
00:14:21,872 --> 00:14:25,004
there’s an introduction to the reading that was in the course pack

213
00:14:25,004 --> 00:14:29,671
and it talked about air pollution episodes in London.

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And we talked about Donora in class a few, a few lectures ago.

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So in those cases, you had water droplets that had both sulfur dioxide

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and particulate matter in them,

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00:14:43,480 --> 00:14:49,145
and that smog again was formed primarily from the particulate matter and smoke.

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And the SO2 that absorbed that can cause in particulate matter causes

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some serious health effects. Now that does not require any sunlight to form.

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That’s, that’s a straight physical phenomenon and the cause of smog

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that we have seen in urban environments and the cause of smog that we see in Beijing.

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So here’s some photos of some traditional smog scenarios.

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It can often occur in the winter when temperature inversions can trap pollutants

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and we form these water droplets with sulfur dioxide and particulate matter.

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Again, this does not require sunlight.

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So, and these are pretty, pretty gnarly conditions.

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I don’t know if you any of you’ve experienced these in a heavy urban environment,

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but they cause respiratory distress and, and other health effects.

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So now we’ll move into photochemical smog and

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the one that’s become a much larger issue of concern.

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So what can cause smog?

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Well again we have these fine particles that are discharged in power plants primarily.

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If we are using diesel fuels,

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those can also have particulate matter in their discharge pipes.

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So again, these fine particles can blend with the water dot,

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droplets in fog and cause this smog, which can be deposited.

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What we’re going to be looking at further will be photochemical smog,

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which is formed primarily due to NOx, meaning NO or NO2.

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I’ll use that as an abbreviation, but NOx, nitrogen oxides,

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that are discharged along with volatile organic compounds in a variety sources.

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Those are discharged from factories.

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You know if you have a boiler that is generating heat,

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that boiler will discharge NOx and some volatile organic compounds.

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Of course at a refinery or other chemical plant as a chemical process,

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you can have NOx and, and VOCs discharged.

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Vehicles will discharge NO as the primary pollutant and VOCs from the tailpipes.

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So you have a number of sources of NOx and VOCs that

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I’ll show you can form ozone in the troposphere.

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Again this is the bad ozone.

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You may recall that the stratospheric ozone,

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that ozone blocks some very powerful UV radiation and

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so we want to keep that ozone in the atmosphere.

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This, this ozone that we’re generating as you’ll see shortly has a number

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of health effects and other chemical effects that are, that are not good.

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So what’s photochemical smog?

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Well we generally have to look at the impact of volatile organic compounds and

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NOx in a photochemical reaction that’s going to generate smog.

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Now in this definition we’re calling smog essentially the photochemical oxidants primarily ozone.

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So this is in again the, these droplets that will contain sulfur dioxide

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and particulate matter, we’re talking primarily about production of ozone.

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One little number to keep in the back of your mind is that

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the National Ambient Air Quality Standard for ozone is 120 ppb,

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and so this is the trip for, for other activities.

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So what’s the big deal with ozone?

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Well it’s an irritant.

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Again, it’s an oxidant and so it can irritate your respiratory system.

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It can be an eye irritant.

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So it’s again something that you don’t want to be around,

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especially if you’re sensitive populations.

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But there are other effects according to, other effects that follow

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from higher ozone levels.

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Ozone actually causes 90% of the damage to agriculture.

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It can impact tree foliage and can stunt growth.

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Crop damage due to ozone may exceed $2 to $3 billion a year,

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which is again a significant part of our agricultural productivity, 2% to 3%.

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Now the benefit is that again a lot of these agricultural areas

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are outside of areas with significant ozone production,

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but ozone is transported in ambient air.

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So it, it has an impact on our, on our agriculture.

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Well tire life, I mean all of us drive vehicles,

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but tires breakdown these days not so much due to typical tread wear,

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but also by sidewalls deteriorating due to the presence of ozone.

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00:19:50,404 --> 00:19:52,063
Again ozone is an oxidant.

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So it’s going to breakdown rubber and it will have an impact on your tires.

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So other evidence of smog damage include fading and cracking of paints

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and some accelerated metal corrosion.

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So we talked a bit about the chemicals that are responsible for smog production.

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When we combust air, you know we use air in to, for combustion,

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it’s a mix of primarily nitrogen and oxygen.

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Well that combustion will cause the formation of NO, which is our primary pollutant.

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But the NO can combine further with oxygen to cause NOx or NO2.

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So this NOx is what will react then with sunlight to, to form this oxygen atom.

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And this oxygen atom is highly reactive and that will combine with oxygen to form ozone.

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So our combustion doesn’t directly form ozone,

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but the combustion product, NOx, will again react with sunlight to form this oxygen atom,

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which will then combine with oxygen to form ozone.

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So ozone doesn’t keep building and building and building.

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Ozone is then degraded by NO.

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It will react with NO to form NO2 and oxygen.

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So you know the, the concentration of ozone in the troposphere

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is a balance between ozone production of course and ozone degradation.

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So looking at this in kind of a process model.

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We have emissions, again whether this comes from a boiler, from a power plant,

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from a vehicle, we’re going to produce NO, which will again form to NO2 formation,

305
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which can again cycle back to NO.

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That NO2 generates free oxygen, which will react with oxygen,

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molecular oxygen to form ozone. So this reaction does require sunlight.

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So you’ll see some temporal variation of course, in the production of ozone,

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you need sunlight to get this oxygen atom produced to form ozone.

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So you see again we have a balance.

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The nitrogen dioxide produces free oxygen, the oxygen atom which produces ozone,

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and yet we have NO that’s going to destroy ozone,

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and that balance is going to determine the ambient ozone level.

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So we if we look at equilibrium ozone concentrations

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as a function of the initial NOx concentration,

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everything is going to be dependent on the ratio of NO2 to NO.

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So we can calculate, we can use equilibrium concentrations to generate this,

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00:23:11,003 --> 00:23:17,085
our ozone concentration as a function of these reaction rate constants,

319
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which will be dependent on sunlight, and our NO2 and NO concentrations.

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00:23:22,270 --> 00:23:30,136
So if we look at the NO2 to NO ratio at .2, at a ratio of .2,

321
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that equilibrium ozone concentration will be pretty low.

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If we start, if we raise that ratio to .6,

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our equilibrium ozone concentration will still be low,

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but it will still be increasing of course.

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But as we get to a ratio of 1,

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then our equilibrium concentration starts to produce ozone

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and it’s greater than the rate that ozone is, is degraded.

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So this equilibrium ratio of NO2 to NO is the,

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00:24:10,404 --> 00:24:13,646
you know the tripping factor that’ll drive whether

330
00:24:13,646 --> 00:24:18,895
we’re producing ozone or whether we’re degrading it.

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00:24:18,895 --> 00:24:21,895
So how do VOCs fit in the mix?

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Well the VOCs don’t generate ozone directly.

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00:24:31,486 --> 00:24:36,003
But again we can have production of this molecular,

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of this atomic oxygen with water to form these two hydroxyl radicals,

335
00:24:41,230 --> 00:24:44,812
and those hydroxyl radicals are very reactive.

336
00:24:44,812 --> 00:24:49,146
Those radicals will react with a hydrocarbon.

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00:24:49,146 --> 00:24:53,480
In this case, you know we’re calling R, our hydrocarbon chain,

338
00:24:53,480 --> 00:24:58,269
this can be methane, ethane, you know a larger hydrocarbon chain.

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00:24:58,269 --> 00:25:01,269
R is just going to be our symbol for those organics.

340
00:25:01,269 --> 00:25:07,230
So it will react with that hydroxyl radical and nitrous oxide and oxygen

341
00:25:07,230 --> 00:25:16,004
to form more of this NO2, as well as the reactive radical

342
00:25:16,004 --> 00:25:23,564
that will continue to form some NO2, and this is kind of an ongoing chain.

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00:25:23,564 --> 00:25:27,404
So this, these hydrocarbons will generate these free radicals

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and kind of fuel the production of NO2.

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00:25:31,479 --> 00:25:40,268
So what happens is we wind up essentially using up the NO that would typically

346
00:25:40,268 --> 00:25:45,003
be used to degrade the ozone, we’re going to form NO2,

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00:25:45,003 --> 00:25:47,537
which will thereby form more ozone.

348
00:25:47,537 --> 00:25:52,603
So this is a kind of a, a positive feedback mechanism

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00:25:52,603 --> 00:25:57,404
where we generate more ozone then is destroyed.

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So in Los Angeles we’ve got some geographic factors

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00:26:02,070 --> 00:26:06,063
that can cause for these buildups of ozone.

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The first is we can have temperature inversions.

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So essentially our mixing height within the urban area is small.

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00:26:14,604 --> 00:26:19,480
It essentially puts a lid on our airshed keeping the, essentially reducing

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00:26:19,480 --> 00:26:25,234
that control volume, so increasing our concentration of ozone.

356
00:26:25,234 --> 00:26:31,736
If we have low wind speeds, again we’ll have fewer air exchanges

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00:26:31,736 --> 00:26:37,564
and that will also increase the concentration of ozone within that control volume.

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Sunlight will drive production of this atomic oxygen,

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00:26:42,896 --> 00:26:48,336
which will again react with molecular oxygen to form ozone.

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And vehicles will produce NO and then NO2, and of course VOCs

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that will fuel this free radical production to generate more NO2.

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00:27:01,404 --> 00:27:08,936
So if we look at the buildup of NO, NO2, and ozone in L.A.,

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00:27:08,936 --> 00:27:17,736
this is a fairly typical sort of production curve of nitrogen dioxide and,

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00:27:17,736 --> 00:27:20,817
and nitric oxide in the atmosphere.

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00:27:20,817 --> 00:27:26,670
Remember that 122 ppb is our maximum daily one-hour average.

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00:27:26,670 --> 00:27:32,501
So this would be sort of the cut-off for the National Air Ambient Quality Standard.

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00:27:32,501 --> 00:27:35,070
So typically we can hit that or come close to hitting

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00:27:35,070 --> 00:27:37,870
that in L.A. in the late morning.

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You know we’ve got commuter traffic.

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We’re generating a lot of VOCs.

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These reactions occur fairly quickly,

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so we’ll get an increase production of, of NO2

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because of the emissions out of the tailpipe,

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as well as the hydroxyl radical formations

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00:27:57,270 --> 00:28:00,479
from the hydrocarbons that are discharged to get a peak

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00:28:00,479 --> 00:28:04,604
of ozone formation in the late morning.

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00:28:04,604 --> 00:28:08,563
If you look in your readings that are some additional figures

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00:28:08,563 --> 00:28:13,314
that show ozone concentration profiles over time.

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00:28:13,314 --> 00:28:16,338
There was a figure in the reading from Massachusetts

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00:28:16,338 --> 00:28:20,337
that showed this sort of morning peak due to commuting and

381
00:28:20,337 --> 00:28:28,403
then a later afternoon/early evening peak because of transportation of,

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00:28:28,403 --> 00:28:34,539
or migration of ozone into that urban airshed at a later time

383
00:28:34,539 --> 00:28:37,202
from another up gradient site.

384
00:28:37,202 --> 00:28:41,480
So ozone in the local atmosphere will be dependent

385
00:28:41,480 --> 00:28:48,404
not only on the sunlight and wind speeds and temperatures

386
00:28:48,404 --> 00:28:51,145
and that big urban commute in the morning,

387
00:28:51,145 --> 00:28:55,205
but you can also have ozone then transported into your urban airshed. Go ahead.

388
00:28:55,205 --> 00:29:01,645
[Student Inaudible]

389
00:29:01,645 --> 00:29:04,896
Probably because the sunlight goes down.

390
00:29:04,896 --> 00:29:07,936
We don’t have as intense of radiation at that time,

391
00:29:07,936 --> 00:29:12,169
which again drives the formation of, of the NO2 and those radicals.

392
00:29:12,169 --> 00:29:17,070
So it’s fairly typical to see this curve drop off later in the day,

393
00:29:17,070 --> 00:29:20,564
because just the sunlight isn’t strong.

394
00:29:20,564 --> 00:29:27,404
Well here’s some photographs of Santiago, Chile.

395
00:29:27,404 --> 00:29:33,735
Fairly similar scenario with L.A. in that you’ve got an urban population in a valley,

396
00:29:33,735 --> 00:29:38,480
and so late morning things are actually not looking too bad,

397
00:29:38,480 --> 00:29:43,536
but by late afternoon with the buildup of vehicle traffic and the sunlight,

398
00:29:43,536 --> 00:29:49,338
we’ve got smog formation that really impacts visibility.

399
00:29:49,338 --> 00:29:55,896
Okay. So we have talked a bit about our box model for urban ozone formation.

400
00:29:55,896 --> 00:29:59,730
Again, the, the parameters to remember that are important

401
00:29:59,730 --> 00:30:04,003
will be the wind velocity, the emission rate, the deposition velocity,

402
00:30:04,003 --> 00:30:08,564
and of course the geometry that you need to set up your control volume.

403
00:30:08,564 --> 00:30:13,482
So you know and we, we can set up these mass balance equations,

404
00:30:13,482 --> 00:30:17,335
that emission rate is going to be a really important number.

405
00:30:17,335 --> 00:30:20,270
Our deposition rate, which is often quite unknown,

406
00:30:20,270 --> 00:30:22,004
is going to be an important number,

407
00:30:22,004 --> 00:30:25,736
and again whether we have any reaction of the material.

408
00:30:25,736 --> 00:30:34,405
Now we can look at box models for ozone including VOCs inputs

409
00:30:34,405 --> 00:30:37,479
and NOx inputs and that’s of course well beyond the,

410
00:30:37,479 --> 00:30:41,562
the scope of this course, but we can come up with models

411
00:30:41,562 --> 00:30:47,938
that will predict ozone formation based on an initial VOC concentration.

412
00:30:47,938 --> 00:30:53,203
So remember when VOC levels are high there’s,

413
00:30:53,203 --> 00:30:58,004
there’s still plenty to convert NO to NO2.

414
00:30:58,004 --> 00:31:04,357
But we have to remember that, that NO destroys ozone, but NO2 creates it.

415
00:31:04,357 --> 00:31:09,002
So this graph just looks at total carbon in an atmosphere and

416
00:31:09,002 --> 00:31:15,896
we certainly see the increase of ozone production with an increase in VOCs.

417
00:31:15,896 --> 00:31:19,002
Now looking at the magnitude of these things,

418
00:31:19,002 --> 00:31:23,895
you know when you’re already out in the kind of plateau area of this curve,

419
00:31:23,895 --> 00:31:26,979
you can look that you know if you reduce VOCs by 20%,

420
00:31:26,979 --> 00:31:31,536
you’re just not going to have much of an impact on ozone production.

421
00:31:31,536 --> 00:31:36,228
You’re really in an insensitive part of the model to VOC production.

422
00:31:36,228 --> 00:31:41,004
You’ve really got to get down to some much lower concentrations of VOCs.

423
00:31:41,004 --> 00:31:44,670
In this case, you know we went from an 80% reduction in VOCs

424
00:31:44,670 --> 00:31:49,480
and that had a 30% impact on ozone production.

425
00:31:49,480 --> 00:31:53,070
So again these models are, are dependent on VOCs,

426
00:31:53,070 --> 00:31:55,480
but once we get out into these plateau areas

427
00:31:55,480 --> 00:32:00,229
it’s going to be fairly insensitive to any reductions in VOCs.

428
00:32:00,229 --> 00:32:08,145
So we look at ozone creation as a function of the NOx concentration.

429
00:32:08,145 --> 00:32:15,768
We have our initial NOx concentrations and our ozone production actually peaks,

430
00:32:15,768 --> 00:32:21,870
and then it starts to drop off. So why does that happen?

431
00:32:21,870 --> 00:32:25,670
I mean you would think intuitively well if I decrease NOx

432
00:32:25,670 --> 00:32:27,813
then I should decrease ozone.

433
00:32:27,813 --> 00:32:35,670
But remember that when we produce NO2 we’ll also produce some NO at some point

434
00:32:35,670 --> 00:32:40,312
and so as we start to produce NO, that’s going to destroy ozone

435
00:32:40,312 --> 00:32:45,604
and it’s going to decrease the ozone concentrations in our model.

436
00:32:45,604 --> 00:32:50,270
So in this case, if our ozone, if our NOx concentrations are high,

437
00:32:50,270 --> 00:32:53,338
let’s say in that 122 ppb range,

438
00:32:53,338 --> 00:32:57,339
you may think well let’s reduce NOx to reduce our ozone,

439
00:32:57,339 --> 00:32:59,936
but actually according to that equilibrium model,

440
00:32:59,936 --> 00:33:04,812
we’ll actually increase the ozone concentrations because we aren’t producing as much NO,

441
00:33:04,812 --> 00:33:09,102
which degrades the ozone.

442
00:33:09,102 --> 00:33:11,396
So you’ve really got see where you are in the model.

443
00:33:11,396 --> 00:33:15,270
You can’t automatically assume that okay I’m going to reduce VOC concentrations,

444
00:33:15,270 --> 00:33:19,811
I’ll get an ozone reduction, or I’m going to reduce NOx concentrations,

445
00:33:19,811 --> 00:33:21,896
I’ll get an ozone reduction.

446
00:33:21,896 --> 00:33:27,534
It really depends on the actual concentrations and where you are in the model.

447
00:33:27,534 --> 00:33:36,811
Okay. We’re going to look, kind of finish up our lecture today

448
00:33:36,811 --> 00:33:39,562
looking at some isopleth diagrams.

449
00:33:39,562 --> 00:33:45,336
It really can provide a roadmap as to how to deal with elevated ozone concentrations.

450
00:33:45,336 --> 00:33:53,538
So we can use these models to essentially come up with a contour map for ozone.

451
00:33:53,538 --> 00:33:55,230
This is really what this is.

452
00:33:55,230 --> 00:34:01,736
So we’ve plotted the ozone concentrations as a function of VOCs and NOx.

453
00:34:01,736 --> 00:34:09,070
So of course as you know we go and increase VOCs and increase NOx concentrations,

454
00:34:09,070 --> 00:34:15,227
our, essentially our isocontour lines for ozone concentrations here will increase.

455
00:34:15,227 --> 00:34:19,167
So using those model calculations for, you can,

456
00:34:19,167 --> 00:34:25,002
if you have a given concentration of VOC and a given concentration of NOx,

457
00:34:25,002 --> 00:34:30,002
you can predict your result in ozone concentration to see where you are on this map.

458
00:34:30,002 --> 00:34:37,669
So if you for example at .6 ppm of VOCs and about 120 ppb of NOx,

459
00:34:37,669 --> 00:34:44,477
you’d expect an ozone concentration of 240 ppb.

460
00:34:44,477 --> 00:34:54,269
So the, so any, any questions about what we’re looking at on these isopleth figures?

461
00:34:54,269 --> 00:34:57,272
So essentially we’re using our equilibrium model.

462
00:34:57,272 --> 00:35:01,561
We’re inputting a given concentration for VOCs, a given concentration for NOx,

463
00:35:01,561 --> 00:35:07,980
and it’s going to tell us really where we are in terms of the ozone concentration.

464
00:35:07,980 --> 00:35:16,070
So we can use these models to try to decide what we’re going to do if,

465
00:35:16,070 --> 00:35:21,403
you know how to address a given ozone concentration.

466
00:35:21,403 --> 00:35:25,231
So in this model we’ve identified what’s called a ridge line and

467
00:35:25,231 --> 00:35:34,312
it really divides where we are in ozone concentrations with respect to NOx versus VOCs.

468
00:35:34,312 --> 00:35:38,602
So if we are looking at this part of these isopleth diagrams,

469
00:35:38,602 --> 00:35:41,269
we’re essentially NOx limited,

470
00:35:41,269 --> 00:35:46,669
which means that the ozone production is really driven by the NOx concentration.

471
00:35:46,669 --> 00:35:53,480
We can vary VOCs all we want, but we’re not going to impact the VOC concentration at all.

472
00:35:53,480 --> 00:35:59,271
Similarly, where in this part of the isopleth diagram, we’re in a VOC limited regime.

473
00:35:59,271 --> 00:36:03,937
So we can change the NOX concentration really all we want,

474
00:36:03,937 --> 00:36:10,403
but, we can kind of go up and down the NOx curve, the NOx concentration,

475
00:36:10,403 --> 00:36:13,764
but we’re not going to change the ozone concentration very much.

476
00:36:13,764 --> 00:36:18,312
We again this is based on the interplay between VOCs and NOx

477
00:36:18,312 --> 00:36:21,137
and their associated rate constants.

478
00:36:21,137 --> 00:36:24,470
Now we’ve got a couple of different ways

479
00:36:24,470 --> 00:36:29,403
to look at ozone concentrations based on, on VOCs.

480
00:36:29,403 --> 00:36:33,269
One method is to use a carbon mass approach.

481
00:36:33,269 --> 00:36:39,313
So for example here, we’re looking at all VOCs essentially as if they were equal.

482
00:36:39,313 --> 00:36:46,336
So compounds with larger masses would have a larger impact on the ozone production.

483
00:36:46,336 --> 00:36:49,669
And, and that’s not a particularly accurate model.

484
00:36:49,669 --> 00:36:54,338
We have another model where we can look at reactive organic gases.

485
00:36:54,338 --> 00:36:57,230
So rather than looking at VOCs as a bulk,

486
00:36:57,230 --> 00:36:59,737
we can look at specific reactive gases and that’s a,

487
00:36:59,737 --> 00:37:01,812
that’s a little more accurate model.

488
00:37:01,812 --> 00:37:05,670
We can look at overall chemical reactivity and

489
00:37:05,670 --> 00:37:07,813
I’ll show you a table that looks at that,

490
00:37:07,813 --> 00:37:10,605
and that’s again a pretty good representation.

491
00:37:10,605 --> 00:37:16,204
But the best methodology that’s out there now looks at maximum incremental reactivity,

492
00:37:16,204 --> 00:37:20,005
and what that, what this ratio is,

493
00:37:20,005 --> 00:37:27,479
is really looks at the amount of ozone produced for a given change in VOC concentrations.

494
00:37:27,479 --> 00:37:31,144
Not all VOCs are created like, alike.

495
00:37:31,144 --> 00:37:35,562
Some will be responsible for a greater ozone production than others,

496
00:37:35,562 --> 00:37:38,869
and so the, we have an opportunity to look at that

497
00:37:38,869 --> 00:37:43,337
through this maximum incremental reactivity value.

498
00:37:43,337 --> 00:37:49,270
The California Air Quality Board essentially uses these values

499
00:37:49,270 --> 00:37:52,066
to look at emissions of specific VOCs.

500
00:37:52,066 --> 00:37:55,095
So again not all VOCs are, are alike.

501
00:37:55,095 --> 00:37:58,811
So by using these, these maximum incremental reactivity numbers

502
00:37:58,811 --> 00:38:05,646
we can get a much more accurate feel for ozone production for a given VOC emission.

503
00:38:05,646 --> 00:38:08,980
Any questions about these approaches?

504
00:38:08,980 --> 00:38:12,936
Okay. So again there were some problems in your reading

505
00:38:12,936 --> 00:38:20,404
that you should take a look at because you were given a set of VOC, NOx,

506
00:38:20,404 --> 00:38:23,871
and ozone concentrations and you have to decide really

507
00:38:23,871 --> 00:38:28,003
where you were on the curve and whether changing the NOx or

508
00:38:28,003 --> 00:38:31,313
changing the VOCs would have an impact on ozone.

509
00:38:31,313 --> 00:38:38,230
So hint-hint for the exam, make sure you understand how to use these diagrams.

510
00:38:38,230 --> 00:38:39,737
All right.

511
00:38:39,737 --> 00:38:44,402
This is a table that looks at a whole series of VOCs

512
00:38:44,402 --> 00:38:48,271
and compares reactivity constants.

513
00:38:48,271 --> 00:38:53,479
In other words, what kind of hydroxyl radical production rate could we have

514
00:38:53,479 --> 00:38:57,816
versus this maximum incremental reactivity number,

515
00:38:57,816 --> 00:39:02,812
which is again a ratio of ozone formed per, per gram of VOC emitted.

516
00:39:02,812 --> 00:39:09,479
And the interesting thing about this table is that these data don’t always match up.

517
00:39:09,479 --> 00:39:14,164
So the hydroxyl radical formation isn’t necessarily parallel

518
00:39:14,164 --> 00:39:18,356
to the maximum incremental reactivity.

519
00:39:18,356 --> 00:39:23,645
Now the numbers that we’re most concerned about with the MIR

520
00:39:23,645 --> 00:39:27,312
are values that are generally 5 and above.

521
00:39:27,312 --> 00:39:35,479
So if we have compounds like ethane, n-octane, propene, trimethyl benzene,

522
00:39:35,479 --> 00:39:38,337
you know those are going to be responsible

523
00:39:38,337 --> 00:39:43,167
for more significant ozone production than compounds like methane or, or.

524
00:39:43,167 --> 00:39:43,467