Carbonaceous species in PM<sub>2.5</sub> at a pair of rural/urban sites in Beijing, 2005–2008

Abstract

Abstract. One-week integrated PM 2.5 samples were collected over four years (2005)(2006)(2007)(2008) at a pair of sites, one rural and one urban site, in the area of Beijing, China. Weekly organic and elemental carbon (OC and EC) concentrations from these samples were measured to investigate their atmospheric concentrations, temporal variation patterns and the factors influencing these aspects. A slightly systematic decrease in annual mean concentration of OC and an opposite trend for EC at both sites was observed. Since OC accounted for about 70 % of total carbon (TC, i.e. OC + EC) the total carbonaceous mass experienced a slight decline on a yearly basis over the study period. Its fraction of PM 2.5 mass at the urban site in 2008 was significantly lower than observed 10 years earlier (1999), indicating that the relative importance of carbonaceous species in PM 2.5 has decreased. In urban Beijing clear seasonal variations (by factors of 1.35 ∼ 3.0) were shown in both OC and EC with higher weekly concentrations and fluctuations in winter and much lower values in summer and spring. The minimum seasonal urban excesses of OC (3.0 µg m −3 ) and EC (1.3 µg m −3 ) occurred in the summer of 2008, which were only one-ninth and one-seventh of their corresponding maximum values, respectively. This reduction in the urban-difference, coupled with more positive stable carbon isotope values of EC at the urban site in that summer relative to the preceding summers, supports that the special clean air campaign for the 2008 Summer Olympic Games very likely had noticeable impact on the ambient concentrations of carbonaceous aerosols in the Beijing area, particularly on the local urban scale. Less consistent seasonal patterns in OC and EC, their scattered correlation, andCorrespondence to: K. He (hekb@tsinghua.edu.cn) higher mass ratios of OC to EC (OC/EC) at the rural site indicate more complex and variable major sources regarding aerosol formation in the rural area. These emission sources include biomass burning during the harvest seasons, widely used high-polluting family stoves and small boilers for cooking and heating with high OC/EC ratios, and a greater relative quantity of secondary organic aerosols.

Five-year record of atmospheric precipitation chemistry in urban Beijing, China

“…This is supported by the fact that the average Na + and Cl − ratio of 2.1 (ranging from 0.7 to 13) was much higher than the reported ratio of 1.16 from seawater (Moller, 1990). This is understandable since Beijing is about 160 km away from the Bohai Sea in the southeast and the wind from that direction in summer is usually mild (Yang et al, 2011a). Factor 2 has high loading for SO 2− 4 , NO − 3 , and NH + 4 , suggestive of the secondary pollution formed in the atmosphere from their precursors -SO 2 , NO x , and NH 3 .…”

“…Lying in the north warm temperate zone, Beijing has typical continental monsoon climate with four distinct seasons. From November-April (dry months), the prevailing airflow from the northwest is dry and cold, while at other times the local winds are moderate and mostly from the south and southeast (Yang et al, 2011a (Fig. 1).…”

“…To improve the capital's air quality, the municipal government has initiated a series of clean air programs starting in 1998 (www.bjepb.gov.cn), and Beijing has been leading the country in progressive introduction of increasingly stringent emission standards for motor vehicles and coal-fired boilers compared to state criteria. As a result, the air quality compliance days have kept increasing thereafter (www.bjepb.gov.cn), but less than what is expected in terms of particulate pollution as compared to SO 2 and NO 2 (Yang et al, 2011a).…”

Assessment of carbonaceous aerosols in Shanghai, China – Part 1: long-term evolution, seasonal variations, and meteorological effects

“…Previous work (Chang et al, 2016) shows that the month of September in Shanghai has the highest planetary boundary layer (PBL), which favors the vertical dispersion of ground-emitted pollutants. Additionally, higher temperature in September could lead to a shift in the gas-particle equilibrium, with more semi-volatile organic compounds (SVOCs) remaining in the gas phase (Yang et al, 2011). In addition, carbonaceous aerosols can also be effectively removed by wet deposition attributed to large amount of precipitation in September .…”

A Comparison of Meteorology-Driven Interannual Variations of Surface Aerosol Concentrations in the Eastern United States, Eastern China, and Europe

“…Observational and modeling studies have reported high aerosol concentrations in the eastern United States (US) (Malm 2004;Park et al 2003Park et al , 2004Walker et al 2012), eastern China (Zhang et al 2012b;Wang et al 2013;Mu and Liao 2014), and Europe (Megaritis et al 2014;Andersson et al 2007) as a result of the large anthropogenic emissions of aerosols and aerosol precursors in these regions (Dutkiewicz et al 2000;Vestreng et al 2007;Hand et al 2012;Mijling et al 2013). Previous studies also showed that the interannual variations (IAVs) of aerosols were significant in the eastern US (Alston et al 2012), eastern China (Yang et al 2011;Mu and Liao 2014), and Europe (Andersson et al 2007). The IAVs in aerosol concentrations were found to be sensitive to the IAVs in anthropogenic emissions of aerosols and aerosol precursors (Mylona 1996;Irie 2005;Ohara et al 2007;Vestreng et al 2007;Xing et al 2013) and in meteorological conditions, since the meteorology modulates the processes of dilution, transport, deposition, and chemical reaction (Andersson et al 2007;Zhao et al 2012;Mu and Liao 2014).…”