Characteristics, sources and formation of aerosol oxalate in an Eastern Asia megacity and its implication to haze pollution

Abstract

A total of 238 samples of PM<sub>2.5</sub> and TSP were analyzed to study the characteristics, sources, and formation pathways of aerosol oxalate in Shanghai in four seasons of 2007. The concentrations of oxalate were 0.07–0.41 μg m<sup>−3</sup> in PM<sub>2.5</sub> and 0.10–0.48 μg m<sup>−3</sup> in TSP, respectively. Oxalate displayed a seasonal variation of autumn>summer>winter>spring in both PM<sub>2.5</sub> and TSP and was dominantly present in PM<sub>2.5</sub> in all samples. Correlation between oxalate and K<sup>+</sup> and high ratio of oxalate/K<sup>+</sup> suggested that biomass burning was a secondary source of aerosol oxalate in Shanghai, in addition to urban VOCs sources (vehicular and industrial emissions), especially in autumn. Secondary formation accounted for the majority of aerosol oxalate in Shanghai, which was supported by the high correlation of oxalate with nss-SO<sub>4</sub><sup>2−</sup>, K<sup>+</sup> and NO<sub>3</sub><sup>−</sup>, proceeding from different mechanisms. Relatively high ambient RH together with high cloud cover was found benefiting the secondary formation of aerosol oxalate. The in-cloud process (aqueous-phase oxidation) was proposed to be likely the major formation pathway of aerosol oxalate in Shanghai, which was supported by the high correlation of oxalate with nss-SO<sub>4</sub><sup>2−</sup> and K<sup>+</sup> , dominant residence of oxalate in droplet mode and result of favorable meteorological condition analysis. High correlation of oxalate and NO<sub>3</sub><sup>−</sup> reflected the OH radical involved oxidation chemistry of the two species in the atmosphere and also suggested that gas-particle surface reactions and evaporation-condensation process were both possible secondary formation pathways of aerosol oxalate in coarser particle mode (>1.0 μm). Aerosol oxalate contributed to the haze pollution and visibility degradation of the local environment. As a major water-soluble organic compound in aerosols, concentration of oxalate showed a distinct negative correlation to the atmospheric visibility, which implied that aerosol organic compounds could play an important role in air quality in Shanghai

Chemical Characterisation of Water-soluble Ions in Atmospheric Particulate Matter on the East Coast of Peninsular Malaysia

“…A positive correlation between oxalate and NH4 + was also observed (R = 0.66, p < 0.001). A similar observation was reported by Jiang et al in a study of aerosol oxalate in Shanghai (Jiang et al, 2011). Using size distribution data, they were able to propose that the correlation was due to the presence of 460 ammonium oxalate in the aerosol.…”

“…-as an indicator for vehicle emissions, nssSO4 2-and NO3 -for secondary formation through different pathways, and K + for biomass burning (Jiang et al, 2011). In this study, there was a relatively strong correlation between oxalate and nssSO4 2-(R = 0.60, p < 0.001), suggesting a common formation pathway of the two species.…”

“…For example, Freitas et al report average oxalate concentrations in TSP at 445 an urban site and a rural site in Londrina City, Brazil of 0.57 and 0.03 µg m -3 respectively (Freitas et al, 2012). Other reported oxalate concentrations in urban TSP include measurements of 0.10 -0.48 µg m -3 in Shanghai (Jiang et al, 2011) and 0.27 µg m -3 in Tokyo (Sempere and Kawamura, 1994).…”

Sources and atmospheric processes impacting oxalate at a suburban coastal site in Hong Kong: Insights inferred from 1 year hourly measurements

“…The seasonal average concentrations (±SD) of oxalate were 0.26 ± 0.10 (spring), 0.24 ± 0.14 (summer), 0.54 ± 0.16 (fall), and 0.36 ± 0.13 µg m −3 (winter) at HKUST and were comparable with the measurements in 2000–2001 (average concentrations of 0.35–0.37 µg m −3 in winter and 0.04–0.17 µg m −3 in summer at three different sites in Hong Kong) [ Yao et al ., ]. Higher concentrations of oxalate in fall and winter were also reported for Shanghai, a city 1000 km north of HK on the east coast of China [ Jiang et al ., ]. For this study, January 2013 was excluded as no oxalate data was available.…”

Chemical characterisation of water-soluble ions in atmospheric particulate matter on the east coast of Peninsular Malaysia

“…For example, Freitas et al (2012) report average oxalate concentrations in PM 10 at an urban site and a rural site in Londrina city, Brazil, of 0.57 and 0.03 µg m −3 respectively. Other reported oxalate con-centrations in urban TSPs (total suspended particles) include measurements of 0.10-0.48 µg m −3 in Shanghai (Jiang et al, 2011) and 0.27 µg m −3 in Tokyo (Sempere and Kawamura, 1994).…”