Understanding Photochemical Smog: Causes, Effects, and Solutions

hi everyone welcome to this lecture on photochemical smog for AP environmental science we're going to talk about two

learning objectives that is topic 7.2 which is photochemical smog the enduring understanding for this is that human

activities have physical chemical and biological consequences for the atmosphere which is pretty much a

repeating theme throughout this entire unit the learning objective explain the causes and effects of photochemical smog

and methods to reduce it we're also going to talk about thermal inversions which is topic 7.3 same enduring

understanding and the learning objective is just describe thermal inversions and its relationship with pollution now we

have already talked about thermal inversions but it was way back in August when we talked about layers of the

atmosphere and Atmospheric composition but it is very applicable here because it really exacerbates uh photochemical

smog um and and winter smog as well so we'll talk about thermal thermal inversions as

well but not as in depth as we would if we hadn't already talked about it vocab is short and sweet and let's just

get right into it so you guys have all heard of smog you've all seen smog but what is smog smog is a portmanteau

meaning a combination of two words so smoke and fog they just took you know smog smog

and we'll typically categorize it either as winter Smog or summer Smog and summer smog is the photochemical smog that

we're going to focus on in this PowerPoint so let's start with winter smog I just have one slide on winter

smog um winter smug as it aptly is called usually occurs during the winter during

the winter we have higher energy demands typically for heat so there's going to be a lot of people burning uh wood

burning stoves maybe pellet stoves um people with fireplaces people with maybe even coal stoves depending on what

part of the world or the country the United States you're at and all of those are going to create smoke and other

particulate matter up in the atmosphere we're also going to have higher energy demands at our power plants so if we're

trying to keep the heat on when it's negative 10 degrees outside we're going to be using electricity for the most

part and a lot of the time that's going to be coming from coal burning power plants or other types of power plants

that are running off of fossil fuels so we're going to have some particulate matter in the atmosphere unless we're

using natural gas power plants okay all of that as well as from traffic and Industry is

going to create all this particulate matter in the atmosphere which is winter smog

and it's going to be exacerbated by thermal inversions which I have on a diagram on the right

but we'll talk about on the next slide so thermal inversion occurs when we have a reversal of the normal air temperature

usually what's going to happen is that the air in the troposphere is going to get colder as you increase in altitude

okay so at the normal situation here on the top right we have warmer air down near the surface right the sunlight

strikes the surface of the Earth warms the ground the Rocks the asphalt the concrete Etc warms the air just above it

and we generally lose temperature as we go higher and higher up think about starting a climb on a mountain you go

you start at the valley below and it's nice and warm and then you climb further in further up into the mountain and you

get colder and colder and colder as you go higher up that mountain same thing

now sometimes there's going to be a temperature inversion or a thermal inversion and that's where we get this

layer of cold air that gets trapped underneath of this layer of warm air usually this is going to happen in a

valley so let's say that we have you can see that there's mountains on this diagram so we got these mountains back

here okay and this city is in a valley what's going to happen is during the night time everything's going to cool

cool off every like it's winter the entire Valley is going to become cold all of the air around it is going to

become cold and then at dawn the Sun is going to rise and that sunlight is going to start

to strike the air above the mountain range but the

mountains are going to shade let's say the city down below so it's not going to get any light and this layer this

inversion layer is going to warm up faster than that cold air down in the valley below

and it's going to create this temperature inversion so you're going to have this warm air that's been heated up

by the sun whereas in the valley below it's going to stay cold air because it's shaded by the mountains and then as the

day progresses yes this will start to warm up a little bit but this cold air that's been trapped there overnight

isn't really going to go anywhere it's going to heat up slower than the air above it

and it's going to trap all those pollutants in it as well because the pollutants are going to want to rise but

they're going to want to but then they'll hit this layer of warm air they won't mix very well and then they go

back down into the City and that leads to something like this where we see this

very distinct layer of smog so all those pollutants from fireplaces from traffic from really anything going on in that

city is getting trapped right there in this case in Denver but this often happens in the winter and

it is referred to as a thermal inversion okay so that's winter smog winter smog again

smoke other pollutants particularly matter other pollutants released in the atmosphere during winter and often

exacerbate by thermal inversions now let's talk about summer smog for the rest of this PowerPoint I'm going to

refer to Summer smog as photochemical smog because that's the term that you need to know okay photochemical smog

occurs when sunlight reacts with water and pollutants in the atmosphere okay so we're going to have some humidity even

if it's a dry area there's going to be some latent humidity especially if we're doing combustion right internal

combustion engines or coal burning power plants natural gas burning power plants any type of combustion is going to

release water vapor so we have our water source humidity or you know even just a tiny bit of water

in the atmosphere sunlight and then primary pollutants especially nitrous oxides and volatile organic compounds

they're going to react in the atmosphere with oxygen with other chemicals or just with the light itself and create a bunch

of secondary pollutants those secondary pollutants include nitric acid peroxide acetyl nitrates aldehydes

and ozone the two that you really need to know for the class is your ozone and your nitric acid

the volatile organic compounds including your hydrocarbons are going to stay in the atmosphere as well not all of them

are going to react but they're going to contribute to some of this photochemical smog too

um maybe if you have uh you know a lot of sulfur oxides sulfur dioxide released in

the atmosphere you might be making some sulfuric acid but in general it's your ozone

and your nitric acid that are going to be your primary constituents of photochemical smog and then a lot of

secondary constituents just depending on what is the primary pollutants in that area Okay because there's going to be a

lot of different variations depending on your local emissions and so I have another diagram of this um

again from industry from internal combustion engines really any type of combustion you're going to release some

nitrogen oxides some nitrous oxides and you're going to release some hydrocarbons that escape

combustion some volatile organic compounds or hydrocarbons um

the Nitric nitrate the Nitric nitrogen oxides geez the nitrogen oxides are going to produce nitric acid they're

also going to produce your pans and your ozone the hydrocarbons that can come off from from

incomplete combustion or just Degas off of um you know chemical solvents or from

oil tanks uh from um gas uh natural gas um Wells those are going to react with a

UV light as well and create your aldehydes including fermaldehyde and acrylin okay but again the ones that you

really need to know is O3 and hno3 which is nitric acid so one thing that I hope that you

noticed on the previous slides that you need for photochemical smog as sunlight you need primarily those ultraviolet

wavelengths um but sunlight in general so photochemical smog is called Summer smog because it occurs most often in the

summer because your sunlight is the highest and you also need heat for these chemical reactions to occur so summer

smog is your photo photochemical smog okay now that's in the um the higher latitudes if you're in the

tropics it can be year-round especially if you're in a dry area someplace like Cairo that really doesn't have a wet

season is going to have photochemical smog pretty much the entire year round or it could just be during the dry

season um some place like Bangladesh may just have a photochemical smog during the dry

season and then during the wet season there's so much rain um that washes these chemicals out of

the atmosphere that that settles them onto the ground that they don't have photochemical smog during the the wet

season okay um if we think about what cities are going

to have photochemical smog it's going to be mostly cities that are Sunny warm and dry think Denver Los Angeles you're not

going to have as much in your wet cities Charlotte North Carolina isn't going to have as much photochemical smog as Los

Angeles or San Diego will just because of the climate right there's more humidity but more importantly it's going

to rain more often during the summer and again that rain absorbs some of these pollutants and deposits them on the on

the on the ground or in your waterways now I'm not saying that's a good thing especially for your soil and your

waterways but it means that you're not breathing in as much smog okay and if we think about what time of

day these emissions start so if we draw a graph of one day and we have the concentration of

these different chemicals so we'll say like chemical concentration the brackets mean

concentration and then time starting early in the morning I'll say that nitrogen nitrous oxide is red

and then that ozone is going to be green okay so early in the day because of people commuting to work your nitrous

oxides are going to Peak and then they might Peak again later on in the day at the afternoon commute

after they've um really um

after there's lots of nitrous oxides in the atmosphere they can react and create ozone and you need that sunlight for the

creation of ozone so your ozone is going to Peak midday and then taper off later on in the evening okay so these Nitro

nitrous oxides are going to create that ozone so it's going to have a different chemical signature your smog is going to

be different at different parts of the day your nitrous oxide is typically peaking early in the morning with a

commute and as people turn on electricity and draw more from the power plants and they increase Supply and then

the ozone follows that and you typically have high levels of ozone midday now quick review of nitrous oxides

strictly speaking nitrous oxides are going to include no which is nitrogen monoxide and NO2 nitrogen dioxide okay

so it's that X is a variable right there either a one or a two however sometimes you will see that nitrous oxide n2o is

included in that too but strictly speaking it shouldn't be now nitrous oxide has a couple other a couple other

names n2o you can say either dinitrogen oxide or dinitrogen monoxide that be probably

probably the best way to say that dinitrogen monoxide but most people just say nitrous oxide

okay um these nitrous oxides are produced from

any type of combustion like I've said especially at high temperatures for most of that we're looking at you know over

50 percent and most of our major cities from Transportation right cars trucks Etc anything that's burning with an

internal combustion engine secondarily to that is going to be your stationary fuel combustion this is stuff

like your power plants or even probably including home stoves and things like that but think power plants for

stationary fuel combustion and then we have some from industry and then miscellaneous okay only three

percent so for photochemical smog these are the most effective cities as of a couple

years ago when I found these articles worldwide we see these cities listed what I want you to notice is that they

are very large cities that are highly populated and that most of these are in that are

in um tropical regions right there's a few exceptions to that right Beijing Moscow are not in tropical regions but

most of these are in those areas where it's um you know umatara also um where it's hot and dry for at least a

portion of the urine all of these it's hot and dry for at least a portion of the year but some of them all year round

then I also have the list of U.S cities okay you notice that um the top what six of them are in

California followed by two in Texas and then another California one further down again hot and dry areas with high

population densities you also notice that none of these U.S cities Los Angeles does not top this

list as the top 10 worldwide okay um because of

the Clean Air act and other similar legislation in the United States we have limited the amount

of photochemical smog in U.S cities the Clean Air Act really has been modeled by many other nations around the

world but you see that there is still some catching up to do especially in developing nations for reducing and

managing and monitoring smog levels now so let's look at the negative human health effects

um there's going to be various human health effects because of the varied chemical composition of smog if we look

back at that list on the previous slide ulambatar that primarily uses coal burning power plants it might be very

different from the effects that you see in you know someplace else that might be mostly from vehicle transportation for

example okay but in general it's going to most avert photochemical smog is going to most diversely affect the young

and old and those with pre-existing conditions when we say pre-existing conditions we mean people that have

asthma people that develop bronchitis when they were very young and have some scarring of their bronchial tissue maybe

people that maybe older folks that smoked for much of their life and have emphysema all right those are

pre-existing conditions that smog will exacerbate um

even stuff that's genetic like uh like multiple sclerosis um you know they will have uh

um more adverse effects to smog um in general it irritates your mucous membranes eyes nose mouth throat mucous

membranes um even down into your lungs and I can therefore weaken your primary immune system especially

um the nose and the throat um because that's where your immune system you know does start

uh you can start to have lung issues with repeated chronic exposure that can include shortness of breath coughing

wheezing asthma bronchitis emphysema potentially cancer okay many of the chemicals in smog especially

formaldehyde are carcinogenic okay I probably spelled that wrong formaldehyde

um sorry about that and then long-term exposure isn't really well known but it has been potentially linked to

alzheimer's disease um birth defects and low birth weight if the mother is repeatedly exposed to smog

and premature death and in fact it's estimated by the World Health Organization that there's 7 million

premature deaths every year from photochemical smog alone that's not including all of the rest of

the pollutants and and your major cities so all the particulate matter and

everything else that's just photochemical smog or smog in general okay so I guess it can include

um particulate matter with winter smog so how can we change this um what are some solutions to reducing

photochemical smog first is switching to renewable energy sources if we're not if we don't have coal burning power plants

then we're not releasing that particular matter the sulfur oxides the nitrous oxides the volatile organic compounds

that can become an off of it we can install devices on those power plants as well if

we do have them to reduce the amount of primary pollutants that go into the atmosphere too but just sticking with

Renewables if you have solar panels on your roof and you have an electric car you were not contributing to the smog

issue directly okay um maybe indirectly from the manufacturing

those panels but it'd be much much less than if you were getting your electricity every day from uh coal

burning power plants okay um your electric vehicle is not going to produce any emissions as it runs

obviously there's going to be emissions tied to the manufacturing but as it runs on the road it's producing no primary

pollutants which is going to create no secondary pollutants and therefore no smog

okay so switching to Renewables is huge reducing your emissions so we've talked about

um Cafe standards the vehicle emission standards in the United States as we reduce the amount as we

make um cars more uh more um efficient run on less fuel we reduce

the amount of um of primary pollutants and therefore secondary pollutants as well and then by

capturing some of those pollutants or by having devices on our vehicles on our power plants that can reduce those

emissions we're therefore reducing smog as well so a catalytic converter on the on your car its job is to

uh react with or cause some of those primary pollutants that re that produce smog that causes them to react and to uh

re be released as just simple nitrogen gas as water vapor and as carbon dioxide so non-smog causing uh chemicals

okay um we can conserve energy increase efficiency right we're producing we're

putting less Demand on those power plants if they are fossil fuel based and even if they're not

using environmentally friendly products that don't release pollutants so like volatile organic compounds I can choose

in my wood shop for example not to use um not to use varnish or lacquer thinner or paint thinner or any of those

chemical based solvents that have the uh that have those volatile organic compounds um coming off of them

volatizing all the time I can instead choose to use something like waxes beeswax maybe that might be more

environmentally friendly as well as um you know in their sourcing as well as reducing the amount of volatile organic

compounds going into the atmosphere okay simple things like monitoring air quality like having smog alert days like

we do or air quality alert days like we do in Denver and saying like you know please do not mow your lawn for example

during these hours because we want to mitigate the amount of primary pollutants that are going in to the

atmosphere during the heat of the day okay so regulating and monitoring air quality buying local products which

reduces shipping and then we have some cool Technical Solutions so smog filtering Towers this is an example of

that there's actually a Dutch company that's taking the carbon from these towers so it's not just reducing

um it's not just reducing smog but it's capturing carbon as well and they're

using that carbon to send to create synthetic diamonds now there's probably huge energy cost into that but it is

um some form of carbon capture as well and then catalytic buildings this is an example of one of those in the bottom

right all of that spiderweb looking stuff out there is um a it's it's like a polymer or a cement alternative that

reacts with ozone and captures that ozone and essentially filters the air kind of like how trees do and in fact

another way to reduce photochemical smog is just to plant trees okay vegetation

um is really good at removing many different chemicals out of the air all right so that was a pretty short

PowerPoint um so let's talk about the Essential Knowledge photochemical smog is formed

when nitrogen oxides of volatile organic Hydro hydrocarbons we are calling those volatore sorry volatile organic

compounds that include hydrocarbons okay they are released into the atmosphere

they relax they react with heat sunlight and water to produce a variety of pollutants and those variety of

pollutants is what we call photochemical smog okay

um many environmental factors affect the formation of photochemical smog again think

um sunlight Heat the amount of precipitation in an area as well as the latitude

nitrogen oxide is produced early in the day ozone concentrations peak in the afternoon and are higher in the summer

because ozone is produced by chemical reaction between oxygen and sunlight so sunlight is higher in the summer so

you're going to have more ozone in the summer and then it's going to Peak midday or in the afternoon because you

need those primary pollutants to be emitted first to their to then react with the with the sunlight which

increases in intensity as you get later in the day uh your volatile organic compounds such

as formaldehyde and gasoline evaporate or sublimate at room temperature remember that evaporation is from liquid

to gas and then sublimate is from a solid to gas and then trees are also natural sources of all to organic

compounds we did not talk about that in this PowerPoint but remember in previous PowerPoints that vegetation whenever you

smell any type of chemical from anything living it's coming from a volat organic compound so the perfume coming from a

rose flower is a volatile organic compound trees are a pretty big source of volatile organic compounds but

nothing compared to fossil fuels or from industry or transportation okay photochemical smog often forms in

urban areas because a large number of Motor Vehicles photochemical smog can be reduced through the reduction of nitrous

oxides and volatile organic compounds and photochemical smog can harm human health okay especially respiratory

problems and then we talked about thermal inversions as well but I'm going to let you read this and kind of skip it

all right so I hope you guys learned something I'll see you on class bye