Journal
ATMOSPHERIC ENVIRONMENT
Volume 141, Issue -, Pages 197-202Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.atmosenv.2016.06.035
Keywords
Haze pollution; Nitrate; Particulate matter; Mitigation strategy; China
Funding
- Strategic Priority Research Program of the Chinese Academy of Sciences [XDB05020000, XDA05100100]
- National Natural Science Foundation of China [41405144, 41230642, 41321064]
- Haze Observation Project [KJZD-EW-TZ-G06-01-04]
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Nitrate salts represent a major component of fine mode aerosols, which play an important role in air pollution worldwide. Based on on-line and off-line aerosol measurements in urban Beijing for both clean and haze conditions, we demonstrate that the absolute and relative concentrations of nitrate increased with visibility degradation (relative humidity), whereas the variations of organics tracked the patterns of mixing-layer height and temperature. We propose that the increase in the relative contribution of nitrate to PM1 observed during the early stages of haze pollution was due to new particle formation, whereas the nitrate formed in PM1-2.5 during the latter stages was due to heterogeneous formation and hygroscopic growth. The increasing trend of nitrate (and also sulfate and ammonium) but decreasing trends of organics during haze development, together with the increase of the NO2/SO2 molar ratio with increasing proximity to downtown Beijing and with visibility degradation, provide further evidence that controlling NOx emissions should be a priority for improving air quality in mega cities. Additional large-scale investigation is required to adequately characterize the regional features of NOx-induced haze pollution in China. Such studies may provide insight into the formation of critical nuclei or the subsequent growth of freshly nucleated particles and advance our understanding of the role of nitrate in new particle formation. (C) 2016 Elsevier Ltd. All rights reserved.
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