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Effect of Changes in Climate and Emissions on Future Sulfate-Nitrate-Ammonium Aerosol Levels in the United States
Global simulations of sulfate, nitrate, and ammonium aerosols are performed for the present day and 2050 using the chemical transport model GEOS-Chem. Changes in climate and emissions projected by the IPCC A1B scenario are imposed separately and together, with the primary focus of the work on future inorganic aerosol levels over the United States. Climate change alone is predicted to lead to decreases in levels of sulfate and ammonium in the southeast U.S. but increases in the Midwest and northeast U.S. Nitrate concentrations are projected to decrease across the U.S. as a result of climate change alone. In the U.S., climate change alone can cause changes in annually averaged sulfate-nitrate-ammonium of up to 0.61 ÎĽg/m3, with seasonal changes often being much larger in magnitude. When changes in anthropogenic emissions are considered (with or without changes in climate), domestic sulfate concentrations are projected to decrease because of sulfur dioxide emission reductions, and nitrate concentrations are predicted to generally increase because of higher ammonia emissions combined with decreases in sulfate despite reductions in emissions of nitrogen oxides. The ammonium burden is projected to increase from 0.24 to 0.36 Tg, and the sulfate burden to increase from 0.28 to 0.40 Tg S as a result of globally higher ammonia and sulfate emissions in the future. The global nitrate burden is predicted to remain essentially constant at 0.35 Tg, with changes in both emissions and climate as a result of the competing effects of higher precursor emissions and increased temperature.Engineering and Applied Science
The formation, properties and impact of secondary organic aerosol: current and emerging issues
Secondary organic aerosol (SOA) accounts for
a significant fraction of ambient tropospheric aerosol and a
detailed knowledge of the formation, properties and transformation
of SOA is therefore required to evaluate its impact
on atmospheric processes, climate and human health.
The chemical and physical processes associated with SOA
formation are complex and varied, and, despite considerable
progress in recent years, a quantitative and predictive
understanding of SOA formation does not exist and therefore
represents a major research challenge in atmospheric
science. This review begins with an update on the current
state of knowledge on the global SOA budget and is followed
by an overview of the atmospheric degradation mechanisms
for SOA precursors, gas-particle partitioning theory
and the analytical techniques used to determine the chemical
composition of SOA. A survey of recent laboratory,
field and modeling studies is also presented. The following
topical and emerging issues are highlighted and discussed
in detail: molecular characterization of biogenic SOA constituents,
condensed phase reactions and oligomerization, the
interaction of atmospheric organic components with sulfuric
acid, the chemical and photochemical processing of organics
in the atmospheric aqueous phase, aerosol formation
from real plant emissions, interaction of atmospheric organic
components with water, thermodynamics and mixtures in atmospheric
models. Finally, the major challenges ahead in
laboratory, field and modeling studies of SOA are discussed
and recommendations for future research directions are proposed
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