Modeling particle number concentrations and sources in the Beijing and Shanghai metropolitan areas with the UCD/CIT...

Particle number concentration (PNC) is a crucial parameter for evaluating the environment, climate, and health effects of particulate matter. Although PNC observation studies have been conducted at various locations, its spatiotemporal variations and source contributions in China remain unclear. In this study, the University of California, Davis/California Institute of Technology air quality model was updated and applied to predict the concentrations and source contributions of particle number in the Beijing and Shanghai metropolitan areas in 2017 (April and July). The comparison of the average of binary and ternary nucleation results against observations shows that good agreement is found for Beijing in April (the normalized mean bias (NMB) = -0.12) and for Shanghai in April (NMB = 0.28) and July (NMB = -0.10). Nucleation is the largest source of PNC in nucleation mode, contributing >90 % (except for 40 % in July of Beijing, likely due to other unaccounted nucleation schemes such as organic nucleation). For PNC in Aitken mode, the two largest sources are transportation (28 %-45 % in Beijing, 15 %-35 % in Shanghai) and nucleation (14 %-45 %, 27 %-73 %). In addition, residential (18 %-22 %) is also important in Beijing. For PNC in accumulation mode, industry is the largest source, contributing over 38 %. PNC from power plant and industry is high near the sources and shows sharp spatial gradient. PNC from residential and transportation is high in urban centers, while PNC from nucleation is higher in relatively clean suburban regions than in the polluted urban center regions in the two cities. Modeling PNCs and sources are useful in future control strategies and epidemiological studies.