Halogens Enhance Haze Pollution in China

Severe and persistent
haze events in northern China, characterized
by high loading of fine aerosol especially of secondary origin, negatively
impact human health and the welfare of ecosystems. However, current
knowledge cannot fully explain the formation of this haze pollution.
Despite field observations of elevated levels of reactive halogen
species (e.g., BrCl, ClNO2, Cl2, HBr) at several
sites in China, the influence of halogens (particularly bromine) on
haze pollution is largely unknown. Here, for the first time, we compile
an emission inventory of anthropogenic bromine and quantify the collective
impact of halogens on haze pollution in northern China. We utilize
a regional model (WRF-Chem), revised to incorporate updated halogen
chemistry and anthropogenic chlorine and bromine emissions and validated
by measurements of atmospheric pollutants and halogens, to show that
halogens enhance the loading of fine aerosol in northern China (on
average by 21%) and especially its secondary components (∼130%
for secondary organic aerosol and ∼20% for sulfate, nitrate,
and ammonium aerosols). Such a significant increase is attributed
to the enhancement of atmospheric oxidants (OH, HO2, O3, NO3, Cl, and Br) by halogen chemistry, with a
significant contribution from previously unconsidered bromine. These
results show that higher recognition of the impact of anthropogenic
halogens shall be given in haze pollution research and air quality
regulation.