In:
Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 20, No. 14 ( 2020-07-31), p. 9101-9114
Abstract:
Abstract. Although there are many studies of particulate matter (PM) pollution in
Beijing, the sources and processes of secondary PM species during haze
periods remain unclear. Limited studies have investigated the PM formation
in highly polluted environments under low- and high-relative-humidity (RH)
conditions. Herein, we present a systematic comparison of species in
submicron particles (PM1) in wintertime Beijing (29 December 2014 to 28 February 2015) for clean periods and pollution periods under low- and high-RH conditions. PM1 species were measured with an aerosol chemical species
monitor (ACSM) and an Aethalometer. Sources and processes for organic
aerosol (OA) were resolved by positive matrix factorization (PMF) with
a multilinear engine 2 (ME-2). The comparisons for clean, low-RH pollution
and high-RH pollution periods are made from three different aspects, namely
(a) mass concentration, (b) mass fraction and (c) growth rate in diurnal
profiles. OA is the dominant component of PM1, with an average mass
concentration of 56.7 µg m−3 (46 %) during high-RH pollution and
67.7 µg m−3 (54 %) during low-RH pollution periods. Sulfate had
higher concentration and mass fraction during high-RH pollution periods,
while nitrate had higher concentration and mass fraction during low-RH
pollution periods. The diurnal variations of nitrate and oxygenated organic
aerosol (OOA) showed a daytime increase in their concentrations during all
three types of periods. Nitrate had similar growth rates during low-RH (0.40 µg m−3 h−1) and high-RH (0.55 µg m−3 h−1)
pollution periods. OOA had a higher growth rate during low-RH pollution
periods (1.0 µg m−3 h−1) than during high-RH pollution
periods (0.40 µg m−3 h−1). In contrast, sulfate had a
decreasing trend during low-RH pollution periods, while it increased
significantly with a growth rate of 0.81 µg m−3 h−1 during
high-RH pollution periods. These distinctions in mass concentrations, mass
fractions and daytime growth rates may be explained by the difference in
the formation processes affected by meteorological conditions. In
particular, photochemical oxidation and aqueous-phase processes may both
produce sulfate and nitrate. The relative importance of the two pathways,
however, differs under different meteorological conditions. Additional OOA
formation under high-RH (〉 70 %) conditions suggests
aqueous-related formation pathways. This study provides a general picture of
the haze formation in Beijing under different meteorological conditions.
Type of Medium:
Online Resource
ISSN:
1680-7324
DOI:
10.5194/acp-20-9101-2020
DOI:
10.5194/acp-20-9101-2020-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2020
detail.hit.zdb_id:
2092549-9
detail.hit.zdb_id:
2069847-1
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