Urban Air Quality
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The composition of the PM2.5 has been investigated and reported: About
30% is organic matter, 7% is elemental carbon, 36% is SNA which includes
sulfate, nitrate, and ammonium compounds, 10% is soil, and 19% is unidentified (Cheng et al., 2016). Sources of organic matter in this air are from primary
combustion emissions of gasoline and diesel vehicles and other combustion
sources. Elemental carbon concentrations in PM2.5 are greater for diesel
emissions compared to gasoline emissions. Secondary organic aerosols are
also important. Smoke from the combustion of wood can be important in
cities where wood is used for winter heating (Cheng et al., 2016). In three
European cities – Amsterdam, Erfurt, and Helsinki – local combustion
processes and secondary particle formation were the most important source
categories of PM2.5 (Vallius et al., 2005).
Although average annual values provide a good overall assessment, the
concentrations of PM2.5 vary with position and time. A good rain washes
particulates from the air and improves air quality. Particulates are also moved
by wind, and air quality is impacted by the typical airflow associated with the
location. Los Angeles is an example of a city where the mountains and hills
reduce airflow and therefore tend to reduce air quality (Parrish et al., 2016).
The importance of wind velocity is also evident in the results for PM2.5 in
Gansu Province in China. In Gansu Province, there are significant emissions
from industrial plants and coal- burning power plants, and variations with
time of day are also significant in these results (Filonchyk et al., 2016).
Lastly, the size distribution and composition of the particulates are
important beyond just if they are larger or smaller than PM2.5. Vehicle
emissions from engines include many particulates that are smaller than 700
nanometers. These very small particulates find their way deep into people’s
lungs, allowing toxic compounds to pass into the bloodstream and find their
way to the brain (Erickson et al., 2017; Block et al., 2012).
3.2.2 Nitrogen Oxides from Combustion
There are three nitrogen oxides – nitrous oxide (N 2 O), nitric oxide (NO), and
nitrogen dioxide (NO 2 ) – that are found in air as gases. Nitrogen dioxide
is the most important of these air pollutants because of concentration and
health impacts. Since more than one nitrogen oxide is often present, “NO x ” is
used to refer to mixtures of these different nitrogen oxides.
Tables 3.1 and 3.2 show the units for nitrogen dioxide in parts per billion
(ppb) in the air. This is a volume fraction or mole fraction unit. The gas concentration can also be in mass/ volume units. For nitrogen dioxide, 100 ppb
is equal to about 188 µg/ m
3
at a pressure of 1 atmosphere and a temperature
of 25°C.
Nitrogen oxides are formed during combustion processes at high
temperatures, with about 47% being from transportation and 34% from
power production and energy use in industry (EEA, 2018). Nitrogen dioxide
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27
The composition of the PM2.5 has been investigated and reported: About
30% is organic matter, 7% is elemental carbon, 36% is SNA which includes
sulfate, nitrate, and ammonium compounds, 10% is soil, and 19% is unidentified (Cheng et al., 2016). Sources of organic matter in this air are from primary
combustion emissions of gasoline and diesel vehicles and other combustion
sources. Elemental carbon concentrations in PM2.5 are greater for diesel
emissions compared to gasoline emissions. Secondary organic aerosols are
also important. Smoke from the combustion of wood can be important in
cities where wood is used for winter heating (Cheng et al., 2016). In three
European cities – Amsterdam, Erfurt, and Helsinki – local combustion
processes and secondary particle formation were the most important source
categories of PM2.5 (Vallius et al., 2005).
Although average annual values provide a good overall assessment, the
concentrations of PM2.5 vary with position and time. A good rain washes
particulates from the air and improves air quality. Particulates are also moved
by wind, and air quality is impacted by the typical airflow associated with the
location. Los Angeles is an example of a city where the mountains and hills
reduce airflow and therefore tend to reduce air quality (Parrish et al., 2016).
The importance of wind velocity is also evident in the results for PM2.5 in
Gansu Province in China. In Gansu Province, there are significant emissions
from industrial plants and coal- burning power plants, and variations with
time of day are also significant in these results (Filonchyk et al., 2016).
Lastly, the size distribution and composition of the particulates are
important beyond just if they are larger or smaller than PM2.5. Vehicle
emissions from engines include many particulates that are smaller than 700
nanometers. These very small particulates find their way deep into people’s
lungs, allowing toxic compounds to pass into the bloodstream and find their
way to the brain (Erickson et al., 2017; Block et al., 2012).
3.2.2 Nitrogen Oxides from Combustion
There are three nitrogen oxides – nitrous oxide (N 2 O), nitric oxide (NO), and
nitrogen dioxide (NO 2 ) – that are found in air as gases. Nitrogen dioxide
is the most important of these air pollutants because of concentration and
health impacts. Since more than one nitrogen oxide is often present, “NO x ” is
used to refer to mixtures of these different nitrogen oxides.
Tables 3.1 and 3.2 show the units for nitrogen dioxide in parts per billion
(ppb) in the air. This is a volume fraction or mole fraction unit. The gas concentration can also be in mass/ volume units. For nitrogen dioxide, 100 ppb
is equal to about 188 µg/ m
3
at a pressure of 1 atmosphere and a temperature
of 25°C.
Nitrogen oxides are formed during combustion processes at high
temperatures, with about 47% being from transportation and 34% from
power production and energy use in industry (EEA, 2018). Nitrogen dioxide