es9b02422_si_001.pdf (2.44 MB)
Fast Photochemistry in Wintertime Haze: Consequences for Pollution Mitigation Strategies
journal contribution
posted on 2019-08-25, 20:29 authored by Keding Lu, Hendrik Fuchs, Andreas Hofzumahaus, Zhaofeng Tan, Haichao Wang, Lin Zhang, Sebastian H. Schmitt, Franz Rohrer, Birger Bohn, Sebastian Broch, Huabin Dong, Georgios I. Gkatzelis, Thorsten Hohaus, Frank Holland, Xin Li, Ying Liu, Yuhan Liu, Xuefei Ma, Anna Novelli, Patrick Schlag, Min Shao, Yusheng Wu, Zhijun Wu, Limin Zeng, Min Hu, Astrid Kiendler-Scharr, Andreas Wahner, Yuanhang ZhangIn
contrast to summer smog, the contribution of photochemistry
to the formation of winter haze in northern mid-to-high latitude is
generally assumed to be minor due to reduced solar UV and water vapor
concentrations. Our comprehensive observations of atmospheric radicals
and relevant parameters during several haze events in winter 2016
Beijing, however, reveal surprisingly high hydroxyl radical oxidation
rates up to 15 ppbv/h, which is comparable to the high values reported
in summer photochemical smog and is two to three times larger than
those determined in previous observations during winter in Birmingham
(Heard et al. Geophys. Res. Lett. 2004, 31, (18)), Tokyo (Kanaya et al. J. Geophys. Res.: Atmos. 2007, 112, (D21)), and New York (Ren et al. Atmos. Environ. 2006,
40, 252–263). The active photochemistry facilitates the production of secondary
pollutants. It is mainly initiated by the photolysis of nitrous acid
and ozonolysis of olefins and maintained by an extremely efficiently
radical cycling process driven by nitric oxide. This boosted radical
recycling generates fast photochemical ozone production rates that
are again comparable to those during summer photochemical smog. The
formation of ozone, however, is currently masked by its efficient
chemical removal by nitrogen oxides contributing to the high level
of wintertime particles. The future emission regulations, such as
the reduction of nitrogen oxide emissions, therefore are facing the
challenge of reducing haze and avoiding an increase in ozone pollution
at the same time. Efficient control strategies to mitigate winter
haze in Beijing may require measures similar as implemented to avoid
photochemical smog in summer.