Long-term real-time measurements of aerosol particle composition in Beijing, China: seasonal variations, meteorological effects, and source analysis
Other literature type
Sun, Y. L.
Wang, Z. F.
Wang, Q. Q.
Fu, P. Q.
Pan, X. L.
Worsnop, D. R.
(issn: 1680-7324, eissn: 1680-7324)
High concentrations of fine particles (PM<sub>2.5</sub>) are frequently observed
during all seasons in Beijing, China, leading to severe air pollution and
human health problems in this megacity. In this study, we conducted
real-time measurements of non-refractory submicron aerosol (NR-PM<sub>1</sub>)
species (sulfate, nitrate, ammonium, chloride, and organics) in Beijing
using an Aerodyne Aerosol Chemical Speciation Monitor for 1 year, from July
2011 to June 2012. This is the first long-term, highly time-resolved
(~ 15 min) measurement of fine particle composition in China.
The seasonal average (±1σ) mass concentration of NR-PM<sub>1</sub>
ranged from 52 (±49) μg m<sup>−3</sup> in the spring season to 62
(±49) μg m<sup>−3</sup> in the summer season, with organics being
the major fraction (40–51 %), followed by nitrate (17–25 %) and
sulfate (12–17 %). Organics and chloride showed pronounced seasonal
variations, with much higher concentrations in winter than in the other
seasons, due to enhanced coal combustion emissions. Although the seasonal
variations of secondary inorganic aerosol (SIA, i.e., sulfate + nitrate +
ammonium) concentrations were not significant, higher contributions of SIA
were observed in summer (57–61 %) than in winter (43–46 %), indicating
that secondary aerosol production is a more important process than primary
emissions in summer. Organics presented pronounced diurnal cycles that were
similar among all seasons, whereas the diurnal variations of nitrate were
mainly due to the competition between photochemical production and
gas–particle partitioning. Our data also indicate that high concentrations
of NR-PM<sub>1</sub> (> 60 μg m<sup>−3</sup>) are usually associated
with high ambient relative humidity (RH) (> 50 %) and that
severe particulate pollution is characterized by different aerosol
composition in different seasons. All NR-PM<sub>1</sub> species showed evident
concentration gradients as a function of wind direction, generally with
higher values associated with wind from the south, southeast or east. This
was consistent with their higher potential as source areas, as determined by
potential source contribution function analysis. A common high potential
source area, located to the southwest of Beijing along the Taihang
Mountains, was observed during all seasons except winter, when smaller
source areas were found. These results demonstrate a high potential impact
of regional transport from surrounding regions on the formation of severe
haze pollution in Beijing.