Nitrate aerosols, formed via nitric acid (HNO) to balance inorganic cations in the particle phase, have constituted a major fraction of fine particulate matters (PM) during wintertime haze events in the North China Plain(NCP), with a progressively increasing contribution to PMmass. HNOis produced through homogeneous and heterogeneous pathways in the atmosphere, but the contribution of the two pathways to nitrate remains elusive. Simulations of a wintertime haze event in the NCP using a source-oriented WRF-Chem model reveal that the homogeneous and heterogeneous pathways contribute 48.4% and 51.6% of near-surface nitrate mass on average, respectively. The heterogeneous pathway dominates the nighttime HNOproduction in the planetary boundary layer, with an average contribution of 83%. Although NOis photolytically liable during daytime, the heterogeneous NOhydrolysis still contributes 10% of HNO. Our study highlights the significantly important role of NOheterogeneous hydrolysis in the nitrate formation during wintertime haze days.

Stringent mitigation measures have reduced wintertime PM2.5 concentrations by 42.2% from 2013 to 2018 in the BTH. The observed nitrate aerosols have not exhibited a significant decreasing trend and constituted a major fraction (about 20%) of the total PM2.5, although the surface-measured NO2 level has decreased by over 20%. It still remains elusive about contributions of nitrogen oxides (NOx) emissions mitigation to the nitrate and PM2.5 level. The WRF-Chem model simulations of a persistent haze episode in January 2019 in the BTH reveal that NOx emissions mitigation does not help lower wintertime nitrate and PM2.5 concentrations under current conditions in the BTH, because the substantial O3 increase induced by NOx mitigation offsets the HNO3 loss and enhances sulfate and secondary organic aerosols formation. Our results are further consolidated by occurrence of the severe PM pollution in the BTH during the COVID-19 outbreak with a significant reduction of NO2.

Predicting how warming-induced shifts in plant species-specific phenology affect species dominance remains challenging. Here, we investigated the effects of experimental warming on plant species-specific phenology and dominance as well as their relations in an alpine meadow on the Tibetan Plateau. Warming significantly advanced phenological firsts (leaf out and first flower dates) for most species, while having variable effects on phenological lasts (leaf senescence and last flower) and full phenological periods (growing season and flower duration). Experimental warming reduced community evenness and differentially impacted the species-specific dominance. Specifically, warming-induced shifts in phenological lasts and full phenological periods, rather than the single phenological firsts, are associated with changes in species dominance. Species with lengthened full phenological periods under warming increased their dominance. Our results advance our understanding of how altered species-specific phenophases can be related to changes in community structure in response to climate change.