21Based on a network of field stations belonging to the Chinese Academy of Sciences (CAS), the 22 "Campaign on atmospheric Aerosol REsearch" network of China (CARE-China) was recently 23 established as the country's first monitoring network for the study of the spatiotemporal distribution 24 of aerosol physical characteristics, chemical components and optical properties, as well as aerosol 25 gaseous precursors. The network comprises 36 stations in total and adopts a unified approach in 26 terms of the instrumentation, experimental standards and data specifications. This ongoing project is 27 intended to provide an integrated research platform to monitor online PM 2.5 concentrations, nine-size 28 aerosol concentrations and chemical component distributions, nine-size secondary organic aerosol 29 (SOA) component distributions, gaseous precursor concentrations (including SO 2 , NOx, CO, O 3 and 30VOCs), and aerosol optical properties. The data will be used to identify the sources of regional 31 aerosols, the relative contributions from nature and anthropogenic emissions, the formation of 32 secondary aerosols, and the effects of aerosol component distributions on aerosol optical properties.
33The results will reduce the levels of uncertainty involved in the quantitative assessment of aerosol 34 effects on regional climate and environmental changes, and ultimately provide insight into how to 35 mitigate anthropogenic aerosol emissions in China. The present paper provides a detailed description 36 of the instrumentation, methodologies and experimental procedures used across the network, as well 37 as a case study of observations taken from one station and the distribution of main components of 38 aerosol over China during 2012.39 40
Abstract. To investigate the characteristics of atmospheric brown
carbon (BrC) in the semiarid region of East Asia, PM2.5 and
size-resolved particles in the urban atmosphere of Xi'an, inland China,
during the winter and summer of 2017 were collected and analyzed for optical
properties and chemical compositions. Methanol extracts (MeOH extracts) were
more light-absorbing than water extracts (H2O extracts) in the optical
wavelength of 300–600 nm and well correlated with nitrophenols, polycyclic
aromatic hydrocarbons (PAHs) and oxygenated PAHs (r > 0.78). The
light absorptions (absλ=365 nm) of H2O extracts and
MeOH extracts in winter were 28±16 and 49±32 M m−1,
respectively, which are about 10 times higher than those in summer, mainly
due to the enhanced emissions from biomass burning for house heating. Water-extracted BrC predominately occurred in the fine mode (< 2.1 µm) during winter and summer, accounting for 81 % and 65 % of the total
absorption of BrC, respectively. The light absorption and stable carbon
isotope composition measurements showed an increasing ratio of absλ=365 nm-MeOH to absλ=550 nm-EC along with an enrichment of
13C in PM2.5 during the haze development, indicating an
accumulation of secondarily formed BrC (e.g., nitrophenols) in the aerosol aging
process. Positive matrix factorization (PMF) analysis showed that biomass burning, fossil fuel combustion,
secondary formation, and fugitive dust are the major sources of BrC in the
city, accounting for 55 %, 19 %, 16 %, and 10 % of the total BrC of
PM2.5, respectively.
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