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 2) emitted by coal combustion. There has been considerable debate regarding the mechanism for SO 2 oxidation. Here we show evidence from field observations of a haze event that rapid oxidation of SO 2 by nitrogen dioxide (NO 2) and nitrous acid (HONO) takes place, the latter producing nitrous oxide (N 2 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 2 by NO 2 , producing HONO which can in turn oxidize SO 2 to yield N 2 O.This mechanism could provide an explanation for sulfate formation under some winter haze conditions.

No abstract

With outbreak of the novel coronavirus disease (COVID-19), immediate prevention and control actions were imposed in China. Here, we conducted a timely investigation on the changes of air quality, associated health burden and economic loss during the COVID-19 pandemic (January 1 to May 2, 2020). We found an overall improvement of air quality by analyzing data from 31 provincial cities, due to varying degrees of NO 2 , PM 2.5 , PM 10 and CO reductions outweighing the significant O 3 increase. Such improvement corresponds to a total avoided premature mortality of 9410 (7273–11,144) in the 31 cities by comparing the health burdens between 2019 and 2020. NO 2 reduction was the largest contributor (55%) to this health benefit, far exceeding PM 2.5 (10.9%) and PM 10 (23.9%). O 3 instead was the only negative factor among six pollutants. The period with the largest daily avoided deaths was rather not the period with strict lockdown but that during February 25 to March 31, due to largest reduction of NO 2 and smallest increase of O 3 . Southwest, Central and East China were regions with relatively high daily avoided deaths, while for some cities in Northeast China, the air pollution was even worse, therefore could cause more deaths than 2019. Correspondingly, the avoided health economic loss attributable to air quality improvement was 19.4 (15.0–23.0) billion. Its distribution was generally similar to results of health burden, except that due to regional differences in willingness to pay to reduce risks of premature deaths, East China became the region with largest daily avoided economic loss. Our results here quantitatively assess the effects of short-term control measures on changes of air quality as well as its associated health and economic burden, and such information is beneficial to future air pollution control.

Mg alkaline-promoted Ni ordered mesoporous catalysts possess enhanced catalytic activities and stabilities toward CO2 methanation due to decreasing CO2 activation energy.