Characteristics and Source Apportionment of Size-Fractionated Particulate Matter at Ground and above the Urban Canopy (380 m) in Nanjing, China

Abstract

In this study, the concentrations and chemical components of size-fractionated particulate matter (PM) in Nanjing at the ground (Gulou, 20 m) and above the urban canopy (Zifeng, 380 m) were sampled and analyzed from 16 November to 12 December in 2016. Higher concentrations of PM10, PM10-2.1, and PM2.1 (108.3 ± 23.4 μg m−3, 47.3 ± 10.6 μg m−3, and 61.0 ± 18.8 μg m−3) were measured at Gulou than those (88.1 ± 21.1 μg m−3, 31.4 ± 6.7 μg m−3, and 56.7 ± 18.6 μg m−3) at Zifeng. The most abundant chemical components for size-fractionated PM were SO42−, NO3−, organic carbon (OC), NH4+, elemental carbon (EC), and crustal elements such as Al, Ca, Fe, and Mg, varying significantly on different particulate sizes. The concentrations of OC and EC were 7.46–19.60 μg m−3 and 3.44–5.96 μg m−3 at Gulou and were 8.34–18.62 μg m−3 and 2.86–4.11 μg m−3 at Zifeng, showing an equal importance in both fine and coarse particles. Nitrate, sulfate, and ammonium were more concentrated in PM2.1, contributing 11.30–13.76 μg m−3, 8.91–9.40 μg m−3, and 5.78–6.81 μg m−3, which was more than in PM10-2.1, which contributed 2.73–5.06 μg m−3, 2.16–3.81 μg m−3, and 0.85–0.87 μg m−3. In contrast, the crustal elements were larger in coarse particles and at the ground level, accounting for 18.6% and 15.3% of the total PM at Gulou and Zifeng. Source apportionment using the chemical mass balance (CMB) model EPA showed that the dominant three sources were secondary nitrate (18.2–24.9%), secondary sulfate (14.5–20.4%), and secondary organic aerosols (15.5–19.6%) for PM10, PM2.1, and PM1.1 at both Gulou and Zifeng during the entire sampling period. However, for PM10-2.1, the largest three contributors were secondary organic aerosols (18.3%), the coal-fired power plant (15.6%), and fugitive dust (14.4%), indicating dusts including construction dust, fugitive dust, and soil dust would contribute more at the ground. The results also showed that the concentrations of PM10, PM2.1, and PM1.1 were lower than the work carried out in the winter of 2010 at the same sampling site by 41.4%, 26.3%, and 24.8%, confirming the improvement of the air quality and the efficient control of PM pollutants.