Chemical characteristics of haze particles in Xi'an during Chinese Spring Festival: Impact of fireworks burning

Fireworks burning releases massive fine particles and gaseous pollutants, significantly deteriorating air quality during Chinese Lunar New Year (LNY) period. To investigate the impact of the fireworks burning on the atmospheric aerosol chemistry, 1-hr time resolution of PM2.5 samples in Xi'an during the winter of 2016 including the LNY were collected and detected for inorganic ions, acidity and liquid water content (LWC) of the fine aerosols. PM2.5 during the LNY was 167 ± 87 μg/m3, two times higher than the China National Ambient Air Quality Standard (75 μg/m3). K+ (28 wt.% of the total ion mass) was the most abundant ion in the LNY period, followed by SO42 − (25 wt.%) and Cl− (18 wt.%). In contrast, NO3− (34 wt.%) was the most abundant species in the haze periods (hourly PM2.5 > 75 μg/m3), followed by SO42 − (29.2 wt.%) and NH4+ (16.3 wt.%), while SO42 - (35 wt.%) was the most abundant species in the clean periods (hourly PM2.5 < 75 μg/m3), followed by NO3− (23.1 wt.%) and NH4+ (11 wt.%). Being different from the acidic nature in the non-LNY periods, aerosol in the LNY period presented an alkaline nature with a pH value of 7.8 ± 1.3. LWC during the LNY period showed a robust linear correlation with K2SO4 and KCl, suggesting that aerosol hygroscopicity was dominated by inorganic salts derived from fireworks burning. Analysis of correlations between the ratios of NO3−/SO42 − and NH4+/SO42 − indicated that heterogeneous reaction of HNO3 with NH3 was an important formation pathway of particulate nitrate and ammonium during the LNY period

Molecular distribution and stable carbon isotopic compositions of dicarboxylic acids and related SOA from biogenic sources in the summertime atmosphere of Mt. Tai in the North China Plain

Molecular distributions and stable carbon isotopic (&delta;13C values) compositions of dicarboxylic acids and related secondary organic aerosols (SOA) in PM2:5 aerosols collected on a day/night basis at the summit of Mt. Tai (1534 m a.s.l.) in the summer of 2016 were analyzed to investigate the sources and photochemical aging process of organic aerosols in the forested highland region of the North China Plain. The molecular distributions of dicarboxylic acids and related SOA are characterized by the dominance of oxalic acid (C2), followed by malonic (C3), succinic (C4) and azelaic (C9) acids. The concentration ratios of C2 = C4, diacid-C = OC and C2 = total diacids are larger in the daytime than in the nighttime, suggesting that the daytime aerosols are more photochemically aged than those in the nighttime due to the higher temperature and stronger solar radiation. Both ratios of C2 = C4 (R2 &gt; 0:5) and C3 = C4 (R2 &gt; 0:5) correlated strongly with the ambient temperatures, indicating that SOA in the mountaintop atmosphere are mainly derived from the photochemical oxidation of local emissions rather than long-range transport. The mass ratios of azelaic acid to adipic acid (C9 = C6), azelaic acid to phthalic aid (C9 = Ph) and glyoxal to methylglyoxal (Gly = mGly) and the strong linear correlations of major dicarboxylic acids and related SOA (i.e., C2, C3, C4, !C2, Pyr, Gly and mGly) with biogenic precursors (SOA tracers derived from isoprene, &alpha;/&beta;-pinene and &beta;-caryophyllene) further suggest that aerosols in this region are mainly originated from biogenic sources (i.e., tree emissions). C2 concentrations correlated well with aerosol pH, indicating that particle acidity favors the organic acid formation. The stable carbon isotopic compositions (&delta;13C) of the dicarboxylic acids are higher in the daytime than in the nighttime, with the highest value (&minus;16:5 &plusmn; 1:9 &permil;) found for C2 and the lowest value (&minus;25:2 &plusmn; 2:7 &permil;) found for C9. An increase in &delta;13C values of C2 along with increases in C2 = Gly and C2 = mGly ratios was observed, largely due to the isotopic fractionation effect during the precursor oxidation process.</p