posted on 2019-01-17, 00:00authored byYanmei Qiu, Qiaorong Xie, Junfeng Wang, Weiqi Xu, Linjie Li, Qingqing Wang, Jian Zhao, Yuntao Chen, Yanfang Chen, Yangzhou Wu, Wei Du, Wei Zhou, James Lee, Chuanfeng Zhao, Xinlei Ge, Pingqing Fu, Zifa Wang, Douglas R. Worsnop, Yele Sun
Water-soluble
organic aerosol (WSOA) constitutes a large fraction
of organic aerosol (OA) and plays an important role in affecting aerosol
hygroscopicity and cloud condensation nuclei formation. Here, we characterized
WSOA in fine particles that were collected at ground level and at
260 m on a meteorological tower in Beijing in winter using offline
aerosol mass spectrometry (AMS) and compared them with the simultaneous
real-time online AMS measurements. Our results showed large increases
in WSOA from nonheating season to heating season by 43% and 53% at
ground level and at 260 m, respectively. WSOA was highly oxidized
in winter with a higher oxygen-to-carbon ratio (O/C = 0.69) at 260
m than at ground level (0.63). On average, WSOA contributed 47% and
52% to the total OA at ground level and at 260 m, respectively. Positive
matrix factorization analysis further showed that primary OA was the
dominant source of WSOA (52–61%) with coal combustion (CCOA)
and biomass burning OA (BBOA) being two major contributors. The vertical
differences in water-soluble CCOA and BBOA, however, were very different
with ubiquitously higher CCOA at 260 m than at ground level. Comparatively,
more than 50% of secondary OA in winter was found to be water-insoluble,
highlighting the influences of fossil emissions. The observed high
water-solubilities of CCOA (42–53%) and BBOA (61–78%)
may have significant implications in severe haze formation in winter
in Beijing through a positive feedback mechanism between substantial
increases in primary emissions during heating season and the subsequent
changes in aerosol liquid water content, radiative forcing, and boundary
layer, which is not yet considered in chemical-transport models.