Version 2 2023-11-03, 17:14Version 2 2023-11-03, 17:14
Version 1 2023-11-01, 12:15Version 1 2023-11-01, 12:15
journal contribution
posted on 2023-11-03, 17:14authored byQianru Zhang, Yuhang Wang, Maodian Liu, Mingming Zheng, Lianxin Yuan, Junfeng Liu, Shu Tao, Xuejun Wang
Outdoor air pollution
causes millions of premature deaths annually
worldwide. Sulfate is a major component of particulate pollution.
Winter sulfate observations in China show both high concentrations
and an accumulation mode with a modal size >1 μm. However,
we
find that this observed size distribution cannot be simulated using
classical gaseous and aqueous phase formation (CSF) or proposed aerosol-processing
formation (APF) mechanisms. Specifically, the CSF simulation underestimates
sulfate concentrations by 76% over megacities in China and predicts
particle size distributions with a modal size of ∼0.35 μm,
significantly smaller than observations. Although incorporating the
APF mechanism in the atmospheric chemical model notably improves sulfate
concentration simulation with reasonable parameters, the simulated
sulfate particle size distribution remains similar to that using the
CSF mechanism. We further conduct theoretical analyses and show that
particles with diameters <0.3 μm grow rapidly (2–3
s) to 1 μm through the condensation of sulfuric acid in fresh
high-temperature exhaust plumes, referred to as in-source formation
(ISF). An ISF sulfate source equivalent to 15% of sulfur emissions
from fossil fuel combustion largely explains both observed size distributions
and mass concentrations of sulfate particles. The findings imply that
ISF is a major source of wintertime micron-sized sulfate in China
and underscore the importance of considering the size distribution
of aerosols for accurately assessing the impacts of inorganic aerosols
on radiative forcing and human health.