Primary and secondary aerosols in Beijing in winter: sources, variations and processes
Winter has the worst air pollution of the year in the megacity of Beijing. Despite extensive winter studies in recent years, our knowledge of the sources, formation mechanisms and evolution of aerosol particles is not complete. Here we have a comprehensive characterization of the sources, variat...
| Main Authors: | , , , , , , , , , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-07-01
|
| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/16/8309/2016/acp-16-8309-2016.pdf |
| Summary: | Winter has the worst air pollution of the year in
the megacity of Beijing. Despite extensive winter studies in recent years,
our knowledge of the sources, formation mechanisms and evolution of aerosol
particles is not complete. Here we have a comprehensive characterization of
the sources, variations and processes of submicron aerosols that were
measured by an Aerodyne high-resolution aerosol mass spectrometer from
17 December 2013 to 17 January 2014 along with offline filter analysis by
gas chromatography/mass spectrometry. Our results suggest that submicron
aerosols composition was generally similar across the winter of different years
and was mainly composed of organics (60 %), sulfate (15 %) and nitrate
(11 %). Positive matrix factorization of high- and unit-mass resolution
spectra identified four primary organic aerosol (POA) factors from traffic,
cooking, biomass burning (BBOA) and coal combustion (CCOA) emissions as well as two
secondary OA (SOA) factors. POA dominated OA, on average accounting for
56 %, with CCOA being the largest contributor (20 %). Both CCOA and BBOA
showed distinct polycyclic aromatic hydrocarbons (PAHs) spectral signatures,
indicating that PAHs in winter were mainly from coal combustion (66 %) and
biomass burning emissions (18 %). BBOA was highly correlated with
levoglucosan, a tracer compound for biomass burning (<i>r</i><sup>2</sup> = 0.93),
and made a considerable contribution to OA in winter (9 %). An
aqueous-phase-processed SOA (aq-OOA) that was strongly correlated with
particle liquid water content, sulfate and S-containing ions (e.g.
CH<sub>2</sub>SO<sub>2</sub><sup>+</sup>) was identified. On average aq-OOA contributed 12 % to
the total OA and played a dominant role in increasing oxidation degrees of OA
at high RH levels (> 50 %). Our results illustrate that
aqueous-phase processing can enhance SOA production and oxidation states of
OA as well in winter. Further episode analyses highlighted the significant
impacts of meteorological parameters on aerosol composition, size
distributions, oxidation states of OA and evolutionary processes of
secondary aerosols. |
|---|---|
| ISSN: | 1680-7316 1680-7324 |