Persistent residential burning-related primary organic particles during wintertime hazes in North China: insights into their aging and optical changes
2021
Abstract. Primary organic aerosols (POAs) are a major component of PM 2.5 in winter
polluted air in the North China Plain (NCP), but our understanding of the
atmospheric aging processes of POA particles and the resulting influences on
their optical properties is limited. As part of the Atmospheric Pollution
and Human Health in a Chinese Megacity (APHH-Beijing) program, we
collected airborne particles at an urban site (Beijing) and an upwind rural
site (Gucheng, Hebei province) in the NCP during 13–27 November 2016 for
microscopic analyses. We confirmed that large numbers of light-absorbing
spherical POA (i.e., tarball) and irregular POA particles with high
viscosity were emitted from domestic coal and biomass burning at the
rural site and were further transported to the urban site during regional
wintertime hazes. During the heavily polluted period (PM 2.5 > 200 µ g m −3 ), more than 60 % of these
burning-related POA particles were thickly coated with secondary inorganic
aerosols (named as core–shell POA–SIA particles) through the aging process,
suggesting that POA particles can provide surfaces for the heterogeneous
reactions of SO 2 and NO x . As a result, during the heavily polluted
period, their average particle-to-core diameter ratios at the rural and
urban sites increased to 1.60 and 1.67, respectively. Interestingly, we
found that the aging process did not change the morphology and sizes of POA
cores, indicating that the burning-related POA particles are quite inert in
the atmosphere and can be transported over long distances. Using Mie theory
we estimated that the absorption capacity of these POA particles was
enhanced by ∼ 1.39 times in the heavily polluted period at the
rural and urban sites due to the “lensing effect” of secondary inorganic
coatings. We highlight that the lensing effect on burning-related POA
particles should be considered in radiative forcing models and authorities should continue to promote clean energy in rural areas to
effectively reduce primary emissions.
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