Abstract
In order to investigate the size distributions and seasonal variations of carbonaceous aerosols (organic carbon (OC) and elemental carbon (EC)), the carbonaceous species were collected in Nanjing, a typical industrial city located in Yangtze River Delta, China, in the summer, autumn, and winter of 2013 and spring of 2014, and then analyzed by using a 9-stage Anderson-type aerosol sampler and DRI Model 2001A Thermal/Optical Carbon Analyzer. OC, EC, secondary organic carbon (SOC), and primary organic carbon (POC) exhibited obvious seasonal variations, with the highest levels in winter (39.1±14.0, 5.7 ± 2.1, 23.6 ± 11.7, and 14.1 ± 5.7 μg·m−3, respectively) and the lowest levels in summer (20.6 ± 6.7, 3.3 ± 2.0, 12.2 ± 3.8 and 8.4 ± 4.1 μg·m−3, respectively), and were mainly centralized in PM1.1 in four seasons. The concentrations of OC in PM1.1 varied in the order of winter > autumn > spring > summer, while EC ranked in the order of autumn > winter > summer > spring. In the PM1.1–2.1 and PM2.1–10, the concentrations of OC and EC decreased in the sequence of winter > spring > autumn > summer. The size spectra of OC, EC, and SOC had bimodal distributions in four seasons, except for EC with four peaks in summer. The size spectra of POC varied greatly with seasons, exhibiting bimodal distribution in winter, trimodal distribution in spring and summer, and four peaks in autumn. The OC/EC ratios were 7.0, 6.3, 7.6, and 6.9 in spring, summer, autumn and winter, respectively, which demonstrated the abundance of secondary organic aerosols in Nanjing. The sources of carbonaceous aerosol varied significantly with seasons, and were dominated by vehicle exhaust, and coal and biomass burning in PM2.1, and dominated by dust, and coal and biomass burning in PM2.1–10.
Highlights
Carbonaceous aerosol fractions, accounting for 10%–50% of particle matter (PM) concentrations, play a key role in visibility, human health, Earth’s radiation balance, and cultural heritage [1,2,3,4,5,6,7,8,9,10].Carbonaceous aerosols are generally divided into organic carbon (OC), elemental carbon (EC), and inorganic carbonate carbon (CC)
Autumn (30.5 μg·m−3 ) > spring (25.2 μg·m−3 ) >summer (20.6 μg·m−3 ) in Nanjing, which was similar to that of EC, which had the average concentrations of 5.7, 4.0, 3.6, and 3.3 μg·m−3 in winter, autumn, spring, and summer, respectively. This phenomenon might be attributed to the monsoon effects, where the air masses in summer were clean due to winds predominantly occurring from the southeastern ocean area or southwestern mountain area (Figure 3)
The East Asian monsoon arrived in spring and autumn, resulting in jumbled air masses mostly from ocean and inland, which corresponded to centered pollutant concentrations
Summary
Carbonaceous aerosol fractions, accounting for 10%–50% of particle matter (PM) concentrations, play a key role in visibility, human health, Earth’s radiation balance, and cultural heritage [1,2,3,4,5,6,7,8,9,10]. Hou et al [46] demonstrated that concentrations of OC and EC on haze days were 1.5–3.9 times higher than those on clean days in Shanghai These studies were mainly focused upon the characteristics of carbonaceous aerosols in PM2.5 or PM10 with few concerns about their size distributions in different seasons. The size distributions of carbonaceous aerosols (OC and EC) were collected over different seasons in Nanjing, a typical industrial city located in Yangtze River Delta, China, and further analyzed by using a 9-stage Anderson-type aerosol sampler and DRI Model 2001A Thermal/Optical Carbon Analyzer. It is important to analyze the size distribution of OC, EC, OC/EC, ratios and SOC for better understanding the sources, formation mechanisms, and control strategy of carbonaceous aerosols in atypical polluted city
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