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atmosphere, especially for ozone and carbon monoxide. Inverse modeling is
required to infer pollutant source strength from observed concentration patterns.
Although it is not a substitute for ground-based air-quality measurements,
satellite-derived data provide important spatial, temporal, and contextual infor-
mation about the extent, duration, transport paths, and distances of pollution
from a source, which is generally not possible with in situ ground-based meas-
urements. For example, Morris et al. (2006) linked increases in surface ozone in
Houston to wildfires in Alaska and western Canada, and Heald et al. (2006)
traced an increase in springtime surface aerosols in the northwestern United
States to anthropogenic sources in Asia. As retrieval algorithms and the spatial
and spectral quality of satellite data have improved, remote sensing has provided
a means of obtaining relatively consistent estimates of air-pollutant exposure
over large areas for health-effects assessments (van Donkelaar et al. 2010;
Hystad et al. 2011), which has facilitated large-scale epidemiologic investi-
gations in settings where monitoring data are inadequate to determine spatial
contrasts (Crouse et al. 2012). Another important trend is the assimilation of
concurrent data from multiple sensors with ground data; that has proved espe-
cially useful in improving estimates of ground-level ozone (Fishman et al.
2008).
Example of Using Emerging Science to Address
Regulatory Issues and Support Decision-Making:
Remote Sensing to Monitor Landfill Gas Emissions
Great progress has been made in reducing or eliminating releases of toxic
substances from concentrated sources (also known as point sources), but moni-
toring and mitigating emissions from so-called area sources has been technically
difficult and remains one of the persistent challenges faced by EPA. Recent ef-
forts to use emerging technology in monitoring provide a glimpse on a very
broad scale of what might be possible with further advances. EPA's National
Risk Management Research Laboratory used a tunable diode laser to perform
optical remote-sensing of fugitive methane, hazardous air pollutants (including
mercury), volatile organic compounds, and nonmethane organic compounds
emitted from three landfills. With multiple measurements of concentrations
along different light paths, the system calculates a mass emission flux for the
entire area. What had been thought to be an excessively expensive monitoring
challenge is now financially and practically manageable (EPA 2012b).
Example of Using Emerging Science to Address Regulatory Issues and
Support Decision-Making: Multipollutant Analysis Standard-Setting
Regulation in the United States is predicated on single-pollutant standards
or control strategies. Improved understanding of health effects of cumulative
and mixed exposures calls for new approaches to standard-setting that consider a
multipollutant approach. The shift will require understanding of the joint behav-
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