es6b03010_si_001.pdf (2.97 MB)
Sources and Processes Affecting Fine Particulate Matter Pollution over North China: An Adjoint Analysis of the Beijing APEC Period
journal contribution
posted on 2016-07-19, 00:00 authored by Lin Zhang, Jingyuan Shao, Xiao Lu, Yuanhong Zhao, Yongyun Hu, Daven K. Henze, Hong Liao, Sunling Gong, Qiang ZhangThe
stringent emission controls during the APEC 2014 (the Asia-Pacific
Economic Cooperation Summit; November 5–11, 2014) offer a unique
opportunity to quantify factors affecting fine particulate matter
(PM2.5) pollution over North China. Here we apply a four-dimensional
variational data assimilation system using the adjoint model of GEOS-Chem
to address this issue. Hourly surface measurements of PM2.5 and SO2 for October 15-November 14, 2014 are assimilated
into the model to optimize daily aerosol primary and precursor emissions
over North China. Measured PM2.5 concentrations in Beijing
average 50.3 μg m–3 during APEC, 43% lower
than the mean concentration (88.2 μg m–3)
for the whole period including APEC. Model results attribute about
half of the reduction to meteorology due to active cold surge occurrences
during APEC. Assimilation of surface measurements largely reduces
the model biases and estimates 6%–30% lower aerosol emissions
in the Beijing–Tianjin–Hebei region during APEC than
in late October. We further demonstrate that high PM2.5 events in Beijing during this period can be occasionally contributed
by natural mineral dust, but more events show large sensitivities
to inorganic aerosol sources, particularly emissions of ammonia (NH3) and nitrogen oxides (NOx) reflecting
strong formation of aerosol nitrate in the fall season.