Environmental Engineering Reference
In-Depth Information
6.1 Interactions Between Climate and Air Quality
A.M. Fiore, H. Levy II, Y. Ming, Y. Fang, and L.W. Horowitz
National Oceanic Atmospheric Administration Geophysical Fluid Dynamics Laboratory
(NOAA GFDL), NJ, USA
Abstract
We present two examples of air pollutant contributions to climate forcing.
First, oxidation of the potent greenhouse gas methane produces tropospheric ozone,
another greenhouse gas and the primary constituent of ground-level smog. Methane
emission controls are thus a “win-win” strategy for jointly addressing air quality
and climate goals, particularly given the availability of low-cost emission control
options. Second is the “win-lose” case of aerosol sulfate, where decreases improve
air quality but lead to additional warming due to decreased scattering of solar
radiation. We highlight the potential for aerosols to change the hydrologic cycle
and key aspects of how climate change may affect air quality, underscoring a need
for evaluating chemistry-climate models with observed relationships between
meteorology and air pollutants to build confidence in future projections.
1. Introduction
Ground-level smog, detrimental to human health and vegetation, is pervasive in
populated world regions. In the United States, over 150 million people live in
counties exceeding air quality standards for ozone (O
3
) or particulate matter
(aerosols), the two major smog constituents (U.S. EPA, 2008). These air pollutants
also influence climate, with tropospheric O
3
the third most important greenhouse
gas after carbon dioxide (CO
2
) and methane (CH
4
), and aerosols exerting a net
cooling influence (Forster et al., 2007).
The major precursors to O
3
that fuel rapid photochemical build-up of O
3
during
regional air pollution episodes are non-methane volatile organic compounds
(NMVOC) and nitrogen oxides (NO
x
), whereas the global burden of tropospheric
O
3
is most sensitive to NO
x
and CH
4
(e.g., Fiore et al., 2002). As CH
4
and O
3
together
are estimated to have contributed nearly half as much radiative forcing from 1750
to 2005 as CO
2
(Forster et al., 2007), controls on CH
4
emissions could help to slow
greenhouse warming (Hansen et al., 2000). Since CH
4
oxidation (in the presence
of NO
x
) contributes to the formation of tropospheric O
3
(Crutzen, 1973), including
in surface air (Fiore et al., 2002), such controls would also decrease O
3
pollution.
In contrast, decreasing tropospheric O
3
through NO
x
controls is relatively climate-
neutral due to opposing influences on O
3
and CH
4
(e.g., Fuglestvedt et al., 1999),
and the forcing from pre-industrial to present is small for O
3
precursor emissions of
NMVOC, carbon monoxide (CO) and NO
x
compared to CH
4
(Shindell et al., 2005).
