A review of current knowledge concerning PM<sub>2. 5</sub> chemical composition, aerosol optical properties and their relationships across China

Abstract

Abstract. To obtain a thorough knowledge of PM 2.5 chemical composition and its impact on aerosol optical properties across China, existing field studies conducted after the year 2000 are reviewed and summarized in terms of geographical, interannual and seasonal distributions. Annual PM 2.5 was up to 6 times the National Ambient Air Quality Standards (NAAQS) in some megacities in northern China. Annual PM 2.5 was higher in northern than southern cities, and higher in inland than coastal cities. In a few cities with data longer than a decade, PM 2.5 showed a slight decrease only in the second half of the past decade, while carbonaceous aerosols decreased, sulfate (SO 2− 4 ) and ammonium (NH + 4 ) remained at high levels, and nitrate (NO − 3 ) increased. The highest seasonal averages of PM 2.5 and its major chemical components were typically observed in the cold seasons. Annual average contributions of secondary inorganic aerosols to PM 2.5 ranged from 25 to 48 %, and those of carbonaceous aerosols ranged from 23 to 47 %, both with higher contributions in southern regions due to the frequent dust events in northern China. Source apportionment analysis identified secondary inorganic aerosols, coal combustion and traffic emission as the top three source factors contributing to PM 2.5 mass in most Chinese cities, and the sum of these three source factors explained 44 to 82 % of PM 2.5 mass on annual average across China. Biomass emission in most cities, industrial emission in industrial cities, dust emission in northern cities and ship emission in coastal cities are other major source factors, each of which contributed 7-27 % to PM 2.5 mass in applicable cities.The geographical pattern of scattering coefficient (b sp ) was similar to that of PM 2.5 , and that of aerosol absorption coefficient (b ap ) was determined by elemental carbon (EC) mass concentration and its coating. b sp in ambient condition of relative humidity (RH) = 80 % can be amplified by about 1.8 times that under dry conditions. Secondary inorganic aerosols accounted for about 60 % of aerosol extinction coefficient (b ext ) at RH greater than 70 %. The mass scattering efficiency (MSE) of PM 2.5 ranged from 3.0 to 5.0 m 2 g −1 for aerosols produced from anthropogenic emissions and from 0.7 to 1.0 m 2 g −1 for natural dust aerosols. The mass absorption efficiency (MAE) of EC ranged from 6.5 to 12.4 m 2 g −1 in urban environments, but the MAE of water-soluble organic carbon was only 0.05 to 0.11 m 2 g −1 . Historical emission control policies in China and their effectiveness were discussed based on available chemically resolved PM 2.5 data, which provides the much needed knowledge for guiding future studies and emissions policies.

Intra-regional transport of black carbon between the south edge of the North China Plain and central China during winter haze episodes

“…In the evening, eBC showed an increasing trend and peaked at about 21:00 LT. Similar diurnal patterns of eBC have also been reported in other areas (Verma et al, 2010;Ji et al, 2017;. In contrast, the diurnal variations of eBC at WH and XY exhibited different patterns during clean and polluted periods.…”

“…3.3 BC/PM 2.5 and BC/CO ratios BC/PM 2.5 and BC/CO ratios are widely used to identify the sources of BC Wang et al, 2011;Verma et al, 2010;Chow et al, 2011). Generally, ratios of BC/PM 2.5 from mobile sources (0.059-0.74) and area sources (0.032-0.33) are higher than those from industrial sources (0.0046-0.03).…”

“…The broadly reported BC sources can be grouped into stationary sources (e.g., industrial emission), area sources (e.g., residential coal/wood combustion, open burning) and mobile sources (e.g., diesel engines) (Chow et al, 2011;Bond et al, 2013). To identify BC sources, several methods including the Aethalometer model, diagnosis ratios and radioactive carbon isotope analysis have been developed (Sandradewi et al, 2008;Verma et al, 2010;Zotter et al, 2017). Chow et al (2011) summarized the ratios of elemental carbon to PM 2.5 (expressed as percentage, %) from various sources, and these ratios have since been used to qualitatively describe BC sources (Y. .…”

Significant Climate Impact of Highly Hygroscopic Atmospheric Aerosols in Delhi, India

“…This is consistent with a recent long‐term observational study in Delhi (Sharma et al, ), which reported an annual averaged F OM in PM 2.5 is in a range of 15%–20% during 2012–2016 (mass of organic matter is usually calculated as 1.4 times of organic carbon). However, the F OM in Beijing is usually in a range of 20%–40% (Hu et al, ; Huang et al, ; Tao et al, ; Yang et al, ), where more than half of the organic matter originates from secondary organic aerosol (SOA; Hu et al, ; Huang et al, ; Jimenez et al, ). Stronger solar radiation in Delhi may increase photochemical reactions and oxidation of volatile organic compounds, therefore, may enhance SOA formation (Guo et al, ; Hu et al, ; McFiggans et al, ; Zhang, Wang, et al, ; Zhu et al, ).…”

The Effects of PM2.5 Concentrations and Relative Humidity on Atmospheric Visibility in Beijing

“…During the last decade, the severe and frequent air pollution events in China have received widespread attention (Shen et al, 2017;Tao et al, 2017;Watts et al, 2015;R. Zhang, 2017).…”