Seasonal variations in high time-resolved chemical compositions, sources, and evolution of atmospheric submicron aerosols in the megacity Beijing
A severe regional haze problem in the megacity Beijing and surrounding areas, caused by fast formation and growth of fine particles, has attracted much attention in recent years. In order to investigate the secondary formation and aging process of urban aerosols, four intensive campaigns were con...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-08-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/17/9979/2017/acp-17-9979-2017.pdf |
| Summary: | A severe regional haze problem in the megacity Beijing and surrounding areas,
caused by fast formation and growth of fine particles, has attracted much
attention in recent years. In order to investigate the secondary formation
and aging process of urban aerosols, four intensive campaigns were conducted
in four seasons between March 2012 and March 2013 at an urban site in
Beijing (116.31° E, 37.99° N). An Aerodyne high-resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS) was
deployed to measure non-refractory chemical components of submicron
particulate matter (NR-PM<sub>1</sub>). The average mass concentrations of
PM<sub>1</sub> (NR-PM<sub>1</sub>+black carbon) were 45.1 ± 45.8, 37.5 ± 31.0, 41.3 ± 42.7, and 81.7 ± 72.4 µg m<sup>−3</sup> in spring,
summer, autumn, and winter, respectively. Organic aerosol (OA) was the most
abundant component in PM<sub>1</sub>, accounting for 31, 33, 44, and 36 %
seasonally, and secondary inorganic aerosol (SNA, sum of sulfate, nitrate,
and ammonium) accounted for 59, 57, 43, and 55 % of PM<sub>1</sub>
correspondingly. Based on the application of positive matrix factorization
(PMF), the sources of OA were obtained, including the primary ones of
hydrocarbon-like (HOA), cooking (COA), biomass burning OA (BBOA) and coal
combustion OA (CCOA), and secondary component oxygenated OA (OOA). OOA, which
can be split into more-oxidized (MO-OOA) and less-oxidized OOA (LO-OOA), accounted
for 49, 69, 47, and 50 % in four seasons, respectively. Totally, the
fraction of secondary components (OOA+SNA) contributed about 60–80 %
to PM<sub>1</sub>, suggesting that secondary formation played an important role in
the PM pollution in Beijing, and primary sources were also non-negligible.
The evolution process of OA in different seasons was investigated with
multiple metrics and tools. The average carbon oxidation states and other
metrics show that the oxidation state of OA was the highest in summer,
probably due to both strong photochemical and aqueous-phase oxidations. It
was indicated by the good correlations (<i>r</i> = 0.53–0.75, <i>p</i> < 0.01)
between LO-OOA and odd oxygen (O<sub><i>x</i></sub> = O<sub>3</sub> + NO<sub>2</sub>), and between
MO-OOA and liquid water content in aerosols. BBOA was resolved in spring and
autumn, influenced by agricultural biomass burning (e.g., field preparation
burnings, straw burning after the harvest). CCOA was only identified in
winter due to domestic heating. These results signified that the
comprehensive management for biomass burning and coal combustion emissions
is needed. High concentrations of chemical components in PM<sub>1</sub> in
Beijing, especially in winter or in adverse meteorological conditions,
suggest that further strengthening the regional emission control of primary
particulate and precursors of secondary species is expected. |
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| ISSN: | 1680-7316 1680-7324 |