Fast sulfate formation from oxidation of SO<sub>2</sub> by NO<sub>2</sub> and HONO observed in Beijing haze.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 32503967.
- Also identified by DOI 10.1038/s41467-020-16683-x and PMC identifier 7275061.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Severe events of wintertime particulate air pollution in Beijing (winter haze) are associated with high relative humidity (RH) and fast production of particulate sulfate from the oxidation of sulfur dioxide (SO<sub>2</sub>) emitted by coal combustion. There has been considerable debate regarding the mechanism for SO<sub>2</sub> oxidation. Here we show evidence from field observations of a haze event that rapid oxidation of SO<sub>2</sub> by nitrogen dioxide (NO<sub>2</sub>) and nitrous acid (HONO) takes place, the latter producing nitrous oxide (N<sub>2</sub>O). Sulfate shifts to larger particle sizes during the event, indicative of fog/cloud processing. Fog and cloud readily form under winter haze conditions, leading to high liquid water contents with high pH (>5.5) from elevated ammonia. Such conditions enable fast aqueous-phase oxidation of SO<sub>2</sub> by NO<sub>2</sub>, producing HONO which can in turn oxidize SO<sub>2</sub> to yield N<sub>2</sub>O.This mechanism could provide an explanation for sulfate formation under some winter haze conditions.