Acidic air pollutants dissolve iron in aerosols and fertilize the ocean.

[1] Particulate water-soluble organic nitrogen (ON) was measured over the South China Sea, the Yellow Sea and at a coastal site at Qingdao in spring 2005 and 2006 to study its impact on the oceanic ecosystem over the China sea. ON contributed ∼30% of the total water-soluble particulate nitrogen over the South China Sea and ∼20% over the Yellow Sea and in Qingdao. More than 70% of the ON existed in the fine mode particles (<2.1 mm). During dust-storm events, ON in the coarse particles (>2.1 mm) increased leading to an increase of that in total suspended particulates (TSP). Factor analysis indicated that ON mainly originated from anthropogenic sources while a relatively small amount was from marine and crustal sources. Urea, on the average, represented ∼8% of the total ON over the marginal sea of China. In the non-dust aerosols, ∼50% of urea existed in the fine mode over the Yellow Sea and Qingdao, but the percentage decreased to ∼30% in the dust aerosols. Free amino acids were generally a minor component of the ON, only accounting for ∼1% of the total ON.

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To assess the relative contributions of traffic emission and other potential sources to high levels of atmospheric ammonia (NH) in urban areas in the wintertime, atmospheric NH and related pollutants were measured at an urban site, ∼300 m from a major traffic road, in northern China in November and December 2015. Hourly average NH varied from 0.3 to 10.8 ppb with an average of 2.4 ppb during the campaign. Contrary to the common perspective in literature, traffic emission was demonstrated to be a negligible contributor to atmospheric NH. Atmospheric NH correlated well with ambient water vapor during many time periods lasting from tens of hours to several days, implying NH released from water evaporation is an important source. Emissions from local green space inside the urban areas were identified to significantly contribute to the observed atmospheric NH during ∼60% of the sampling times. Evaporation of predeposited NH through wet precipitation combined with emissions from local green space likely caused the spikes of atmospheric NH mostly occurring 1-4 h after morning rush hours or after and during slight shower events. There are still ∼30% of the data samples with appreciable NH level for which major contributors are yet to be identified.

[1] Atmospheric deposition can deliver new nutrients to the surface water and support primary productivity. Here we report a phytoplankton bloom that developed in the Yellow Sea in the spring of 2007 3-4 days following a dust storm accompanied by precipitation. Our data indicate that atmospheric deposition dominated the supply of new nutrients to the surface water in the central Yellow Sea during the dust event. Dust-derived nitrogen (N) supply was sufficient to support the observed phytoplankton growth, while, dust-derived iron (Fe) supply far exceeded that required by the biota. Granger causality test results further supported that dust-derived nutrients deposition was the cause for the observed bloom with a lag of 3-5 days. Our results contribute to the growing database linking phytoplankton blooms to atmospheric deposition derived fertilization effects. Both dry and wet deposition contributed nutrients to the surface ocean during this event; however, the nutrient loading from dry deposition alone was not sufficient to satisfy the demand of the phytoplankton in this bloom event.

Satellite chlorophyll a (Chl a) concentrations and estimated primary production in the coastal seas of China were correlated with Asian dust events during 1998–2008. Dust events were identified using two approaches, i.e., historical record and satellite aerosol index (AI). Severe and very severe dust events correlated well and positively with Chl a concentrations and primary production in the south Yellow Sea and East China Sea, but it was not statistically significant in the Bohai Sea and the north Yellow Sea. In the south Yellow Sea, Chl a concentration and primary production increased and eventually bloomed 1–21 days after the occurrence of the 16 out of 22 dust storms. Granger causality test showed that AI, photosynthetically available radiation (PAR) and sea surface temperature (SST) did Granger cause primary production in the Yellow Sea, suggesting that past values of the above three variables contain statistically meaningful information about current values of primary production. A stepwise multiple linear regression was used to examine the relative importance of the three factors. PAR and SST accounted for most of the variability of primary production in the north Yellow Sea, while AI was not quite as useful. In the south Yellow Sea, PAR and AI accounted for most of the variability of primary production for all storms; in addition, spring algae blooms were due to dust particles transported in the <3 km layer of the atmosphere which passed through the loess plateau and/or megacities, while the higher‐level (>5 km) dusts, originated mainly from the Taklimakan Desert, Mongolia, and/or west of Inner Mongolia, had no impact.

Abstract. In the summer of 2017, heavy ozone pollution swamped most of the North China Plain (NCP), with the maximum regional average of daily maximum 8 h ozone concentration (MDA8) reaching almost 120 ppbv. In light of the continuing reduction of anthropogenic emissions in China, the underlying mechanisms for the occurrences of these regional extreme ozone episodes are elucidated from two perspectives: meteorology and biogenic emissions. The significant positive correlation between MDA8 ozone and temperature, which is amplified during heat waves concomitant with stagnant air and no precipitation, supports the crucial role of meteorology in driving high ozone concentrations. We also find that biogenic emissions are enhanced due to factors previously not considered. During the heavy ozone pollution episodes in June 2017, biogenic emissions driven by high vapor pressure deficit (VPD), land cover change and urban landscape yield an extra mean MDA8 ozone of 3.08, 2.79 and 4.74 ppbv, respectively, over the NCP, which together contribute as much to MDA8 ozone as biogenic emissions simulated using the land cover of 2003 and ignoring VPD and urban landscape. In Beijing, the biogenic emission increase due to urban landscape has a comparable effect on MDA8 ozone to the combined effect of high VPD and land cover change between 2003 and 2016. In light of the large effect of urban landscape on biogenic emission and the subsequent ozone formation, the types of trees may be cautiously selected to take into account of the biogenic volatile organic compound (BVOC) emission during the afforestation of cities. This study highlights the vital contributions of heat waves, land cover change and urbanization to the occurrence of extreme ozone episodes, with significant implications for ozone pollution control in a future when heat wave frequency and intensity are projected to increase under global warming.

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