Hello everybody! My name is Zohir Chowdhury, and today's topic is about criteria air pollutants and
we'll be focusing on three criteria air pollutants nitrogen oxides or NOx sulfur oxides or Sox and
ozone o3 so there are six criteria criteria air pollutants LED carbon monoxide nitrogen oxides
sulfur oxides ozone and particulate matter pm10 and 2.5 and as I mentioned in the introductory
slide our focus will be on nitrogen oxides sulfur oxides and ozone Metron oxides is expressed as
NOx to designate the various oxides form of a nitrogen and the sulfur oxides is expressed as
Sox to designate the various oxide forms of the sulfur in general so2 or sulfur dioxide because
it's dominant that's surface ox sometimes we also say sulfur dioxide so NOx and Sox NOx or nitrogen
oxides the major sources are from vehicles and industry and it is an ozone precursor which
we'll discuss about ocean in a few minutes what precursor mean that it is used in the formation
of ozone and in terms of health outcomes it is a mild respiratory irritant and major oxide forms
are n2 all nitrous oxide and all night twick oxide and o2 nitrogen dioxide then n2o5 nitrogen Penta
oxide and as well as ammonia but the dominant form that is known as NOx it's a combination
of a no and no2 so these two together is known as NOx a no and no2 not the other ones sulfur oxides
or Sox the major source of Sox is power plants that uses high sulfur coal as well as diesel
also because diesel also has sulfur in it as a contaminant and once diesel or coal is burned it
produces a so sulfur oxide as well as sulfur dioxide which eventually hood more oxygen it
becomes sulfur trioxide however in the air sulfur dioxide is more dominant than the other ones and
so sulfur oxides is mostly expressed in terms of sulfur dioxide with respect to health outcomes
sulfur dioxide or software oxides combined they are respiratory irritant both NOx and Sox they
lead to acid deposition they can be dry deposited in the in the soil from the air or they can be wet
deposited wet deposition means the rain combines with the NOx and Sox that is floating in the air
and eventually NOx and Sox they become nitrogen dioxide net nitric acid and sulfuric acid so NOx
become nitric acid and Sox become sulfuric acid and it leads to significant acidity in the rain
in fact you can see that in the west coast the pH of rain is relatively not very acidic it is
mildly acidic typically rain is mildly acidic but as you go to the east coast mostly in the north
east and southeast you can see that the pH in the rain it's much much lower and the reason is that
there's a lot of coal burning power plants all in all over here which leads to a significant amount
of Sox in the air which in turn leads to sulfuric acid and increases the acidity in the in the ring
the last criteria pollutant that we'll discuss is ground level ozone it is also known as mark
so let's not confuse ground level ozone with stratospheric ozone both stratospheric ozone
and ground-level ozone they are the same chemical ozone however the ground-level ozone is the one
that causes major problem to health because it leads to organisms not being able to tolerate the
higher level of ozone at the ground level whereas if also missing the stratosphere is extremely
protective because it absorbs ultraviolet radiation and leads to protection of skin
and many other issues that can arise from high ultraviolet exposure so the chemical reaction
between NOx which we introduced earlier and VOCs also which stands for volatile organic
compounds together in the presence of sunlight leads to ozone formation so ground-level ozone
is formed when you have NOx nitrogen oxides do you see volatile organic compounds and you have
sunlight as well as heat together this leads to the reaction moving forward and producing ozone
at that so when does high ozone arise and where because of the sunlight and heat would expect high
ozone in the summertime and where you can pretty much imagine anywhere where you have all of these
ingredients NOx and VOCs and you can see that NOx and VOCs they arise from industrial stationary
sources as well as mobile sources such as trucks and vehicles so typically cities and nearby cities
areas where there's a lot of Industry and vehicles and you have a lot of sunlight so next to the
tropics or higher latitude where there's enough sunlight and heat especially in the summertime
ozone there's no threshold what no threshold means is that any concentration even small can lead to
adverse health effects of ozone acute exposure to ozone is to coughing chest pain headaches eye and
throat irritation now Ziya asthma attacks as well as loss of lung capacity and respiratory damage
but ozone also has chronic exposure so with repeated chronic exposure it leads to changes
to immune system aging of lung tissue loss of lung tissue susceptibility to respiratory infection and
so a lot of problems from also exposure and ozone unfortunately in the u.s. it's a main cause of
concern over 50% of the US population population resides in areas that are not in attainment which
means that it does not meet US EPA national ambient air quality standards as a result a
lot of the people in the u.s. they are a potential risk of high level of ozone related health effects
Houston is one example as well as Los Angeles that is always in the news among the worst cities in
the US as well as Atlanta Georgia Denver Phoenix I think these are also have been coming over the
last few years and in North America Mexico City has the highest ozone levels okay so that's a
quick introduction of criteria air pollutants NOx Sox and ozone thank you for listening