Persistent sulfate formation from London Fog to Chinese haze

Abstract

Sulfate aerosols exert profound impacts on human and ecosystem health, weather, and climate, but their formation mechanism remains uncertain. Atmospheric models consistently underpredict sulfate levels under diverse environmental conditions. From atmospheric measurements in two Chinese megacities and complementary laboratory experiments, we show that the aqueous oxidation of SO 2 by NO 2 is key to efficient sulfate formation but is only feasible under two atmospheric conditions: on fine aerosols with high relative humidity and NH 3 neutralization or under cloud conditions. Under polluted environments, this SO 2 oxidation process leads to large sulfate production rates and promotes formation of nitrate and organic matter on aqueous particles, exacerbating severe haze development. Effective haze mitigation is achievable by intervening in the sulfate formation process with enforced NH 3 and NO 2 control measures. In addition to explaining the polluted episodes currently occurring in China and during the 1952 London Fog, this sulfate production mechanism is widespread, and our results suggest a way to tackle this growing problem in China and much of the developing world.sulfate aerosol | severe haze | pollution | human health | climate

Isotopic constraints on heterogeneous sulphate production in Beijing haze

“…(9)). So we also predicted the AWC, pH and I s in stable mode (assuming that bulk aerosols crystallize 187 once saturation is exceeded), which is consistent with Wang et al(2016).The input of observed inorganic ion concentrations 188 and meteorological parametersare summarized in Table S4. Since gaseous NH 3 was not measured in our campaign, we used 189 the empirical equation NH 3 (ppb) = 0.34×NO X (ppb)+0.63, derived from observations of Meng et al(2011) in Beijing winter,190 to estimate the NH 3 concentrations.…”

“…7b). The high I s suggested aerosol 302 water was non-ideal and thus the influence of I s on reaction rate constants (Table S3) and effective Henry's law constantsthe range of 7.5 to 7.8 with a mean of (7.6±0.1), consistent with bulk aerosol pH (7.63±0.03) calculations during a haze 305 event in Beijing 2015 predicted by Wang et al(2016). The bulk aerosol pH calculated assuming metastable state was in the 306 range of 3.4 to 7.6 with a mean of (4.7±1.1), consistent with the mean value of 4.2 calculated in metastable aerosol 307 assumption during severe haze in Beijing 2015-2016 by Liu et al(2017).…”

“…Due to the 60 strong pH-dependence of these two pathways and the large variability of model calculated aerosol pH in Beijing haze 61 (Cheng et al, 2016;Wang et al, 2016;Liu et al, 2017), the relative importance of these two pathways is difficult to constrain. …”

The underappreciated role of nonvolatile cations on aerosol ammonium-sulfate molar ratios

“…This method reports the pH for a HSO4 -/SO4 2-aerosol system similar to the fine particle pH predicted by a thermodynamic modeling used in this study (Guo et al, 2015)) has led to the use of measurable aerosol properties as acidity proxies, such as aerosol ammoniumsulfate ratio or ion balances (e.g. (Paulot and Jacob, 2014;Wang et al, 2016;Silvern et al, 2017)). Recent work has shown that 10 acidity proxies are not uniquely related to pH, which in turn strongly questions any conclusions derived from its use.…”

Lower SO₂ Emissions in the Sintering Process Utilizing the Difference of Sulphur Contents of Iron Ores

“…7) Germany, Japan and other developed countries have taken the lead in treating the sintering flue gas pollutants and issued national standards to limit the pollutants emissions in the sintering process. China began comparatively later for controlling the sintering pollutants.…”