indicating that sources in the neighboring environment must also be considered in the analysis of
overall exposure. Measuring air quality is therefore not a simple matter of purchasing machines.
They need to be carefully located, and the measurements are best coupled with other data such as
meteorology and with numerical models that help
provide additional value with the measured
numbers.
Natural Sources
A 2006 WHO study (Fig. 7) indicates that PM 10
concentrations in Asia and Latin America are
higher than are observed in Europe and North
America [1]. The highest particle levels are
observed in Asia and are attributed to forest
fires, poor fuel quality, and aeolian (windblown)
dust. Wind erosion originating especially in the
deserts of Mongolia and China contributes to the
general level of PM in the region.
Polycyclic Aromatic Hydrocarbons (PAH)
and Urban Air Quality
Sources and Emissions of PAHs
Polycyclic aromatic hydrocarbons are a group of
chemicals that are formed during incomplete
burning of coal, oil, gas, wood, garbage, or other
organic substances, such as tobacco and
charbroiled meat. There are more than 100 different PAHs. PAHs generally occur as complex mixtures normally as part of combustion products
such as soot, not as single compounds.
PAHs can also be found in materials such as
crude oil, coal, coal tar pitch, creosote, and roofing
tar. There are numerous other sources [49, 50].
In the air they are either attached to dust particles or as solids in airborne soil or sediment. This is
of great concern due to the mutagenic [51] and
carcinogenic [52] properties of PAHs; the US
Agency for Toxic Substances and Disease Registry
[50] has listed 17 PAHs as of priority concern with
respect to their toxicological profile.
PAHs that have been studied in urban and other
areas appear to represent only a fraction of a
percent of the ambient particle mass [53]. However, there are compelling arguments that the
previously commonly employed measurement
techniques produced artifacts. Despite the toxicological profile of PAHs, no country has mandatory
guidelines with respect to their ambient air quality
standards [54].
Sampling Artifacts in Measuring PAHs
In order to reduce the risk of sampling artifacts [52]
in the spring of 2003, the Mexico City Metropolitan
Area (MCMA) air quality campaign employed three
independent methods to measure particle bound
PAHs [57, 58]. Peak concentrations of PAHs on
the order of 120 ng m
À3 during the morning rush
hour were observed in excellent agreement that 20%
of the vehicles account for 50% of the PAH emissions [59]. Like other atmospheric gaseous and
particulate constituents, PAHs are removed from
the atmosphere by wet or dry deposition and may
also be converted or degraded in heterogeneous
processes. Despite the systematic approach, there
may have been significant concentrations of very
toxic and very reactive PAHs in the MCMA atmosphere that were missed due to filter reaction artifacts [58], thus attesting to how complicated
measuring PAHs is as a part of air monitoring programs and the need for further development.
Long-Range Transport of PAH
Together with the local emission, the long-range
transport of PAHs is of a concern. PAHs are designated as one of the persistent toxic substances in
central and northeast Asia under the Stockholm
Convention (UNEP, 2002). It has been demonstrated
that transformation processes can lead to PAHs
which are more toxic than their precursors [57].
The source apportionment of particulate PAHs
at Seoul, Korea, during a measurement campaign
between August 2002 and December 2003 was
analyzed [60] by applying the US EPA
(2004) chemical mass balance (CMB) model.
Seoul is in the atmospheric footprint of major
coal-burning industries and power plants of China
and Japan, as well as contributing itself to the
Northeast Asia particle footprint. In Seoul, just
as in the MCMA, gasoline and diesel vehicles
accounted for 31% of the measured PAHs and
thus were the major sources. Daily and seasonal
variations were noted and attributed to differences
Urban Air Quality: Sources and Concentrations
209
overall exposure. Measuring air quality is therefore not a simple matter of purchasing machines.
They need to be carefully located, and the measurements are best coupled with other data such as
meteorology and with numerical models that help
provide additional value with the measured
numbers.
Natural Sources
A 2006 WHO study (Fig. 7) indicates that PM 10
concentrations in Asia and Latin America are
higher than are observed in Europe and North
America [1]. The highest particle levels are
observed in Asia and are attributed to forest
fires, poor fuel quality, and aeolian (windblown)
dust. Wind erosion originating especially in the
deserts of Mongolia and China contributes to the
general level of PM in the region.
Polycyclic Aromatic Hydrocarbons (PAH)
and Urban Air Quality
Sources and Emissions of PAHs
Polycyclic aromatic hydrocarbons are a group of
chemicals that are formed during incomplete
burning of coal, oil, gas, wood, garbage, or other
organic substances, such as tobacco and
charbroiled meat. There are more than 100 different PAHs. PAHs generally occur as complex mixtures normally as part of combustion products
such as soot, not as single compounds.
PAHs can also be found in materials such as
crude oil, coal, coal tar pitch, creosote, and roofing
tar. There are numerous other sources [49, 50].
In the air they are either attached to dust particles or as solids in airborne soil or sediment. This is
of great concern due to the mutagenic [51] and
carcinogenic [52] properties of PAHs; the US
Agency for Toxic Substances and Disease Registry
[50] has listed 17 PAHs as of priority concern with
respect to their toxicological profile.
PAHs that have been studied in urban and other
areas appear to represent only a fraction of a
percent of the ambient particle mass [53]. However, there are compelling arguments that the
previously commonly employed measurement
techniques produced artifacts. Despite the toxicological profile of PAHs, no country has mandatory
guidelines with respect to their ambient air quality
standards [54].
Sampling Artifacts in Measuring PAHs
In order to reduce the risk of sampling artifacts [52]
in the spring of 2003, the Mexico City Metropolitan
Area (MCMA) air quality campaign employed three
independent methods to measure particle bound
PAHs [57, 58]. Peak concentrations of PAHs on
the order of 120 ng m
À3 during the morning rush
hour were observed in excellent agreement that 20%
of the vehicles account for 50% of the PAH emissions [59]. Like other atmospheric gaseous and
particulate constituents, PAHs are removed from
the atmosphere by wet or dry deposition and may
also be converted or degraded in heterogeneous
processes. Despite the systematic approach, there
may have been significant concentrations of very
toxic and very reactive PAHs in the MCMA atmosphere that were missed due to filter reaction artifacts [58], thus attesting to how complicated
measuring PAHs is as a part of air monitoring programs and the need for further development.
Long-Range Transport of PAH
Together with the local emission, the long-range
transport of PAHs is of a concern. PAHs are designated as one of the persistent toxic substances in
central and northeast Asia under the Stockholm
Convention (UNEP, 2002). It has been demonstrated
that transformation processes can lead to PAHs
which are more toxic than their precursors [57].
The source apportionment of particulate PAHs
at Seoul, Korea, during a measurement campaign
between August 2002 and December 2003 was
analyzed [60] by applying the US EPA
(2004) chemical mass balance (CMB) model.
Seoul is in the atmospheric footprint of major
coal-burning industries and power plants of China
and Japan, as well as contributing itself to the
Northeast Asia particle footprint. In Seoul, just
as in the MCMA, gasoline and diesel vehicles
accounted for 31% of the measured PAHs and
thus were the major sources. Daily and seasonal
variations were noted and attributed to differences
Urban Air Quality: Sources and Concentrations
209