Characteristics of fine particle matter at the top of Shanghai Tower

[摘要] To investigate the physical and chemical processes offine particle matter (PM) at the mid-upper planetary boundary layer (PBL), weconducted 1-year continuous measurements of fine PM, thechemical composition of non-refractory submicron aerosol (NR-PM 1 ) , andsome gas species (including sulfur dioxide, nitrogen oxides, and ozone) at anopening observatory ( ∼  600 m) at the top of Shanghai Tower(SHT), which is China's first and the world's second highest buildinglocated in the typical financial central business district of Shanghai,China. This is the first report on the characteristics of fine particlesbased on continuous and sophisticated online measurements at the mid-upperlevel of the urban PBL. The observed PM 2.5 and PM 1 mass concentrationsat SHT were 25.5  ±  17.7 and 17.3  ±  11.7  µ g m −3 ,respectively. Organics, nitrate (NO 3 ) , and sulfate (SO 4 ) occupiedthe first three leading contributions to NR-PM 1 at SHT, accounting for35.8 %, 28.6 %, and 20.8 %, respectively. The lower PM 2.5 concentration was observed at SHT by 16.4 % compared with that near thesurface during the observation period. It was attributed to the decreasednighttime PM 2.5 concentrations (29.4 % lower than the surface) at SHT inall seasons due to the complete isolations from both emissions and gasprecursors near the surface. However, daytime PM 2.5 concentrations at SHTwere 12.4 %–35.1 % higher than those near the surface from June to October,resulted from unexpected larger PM 2.5 levels during early to middleafternoon at SHT than at the surface. We suppose the significant chemicalproduction of secondary aerosols existed in the mid-upper PBL, because strongsolar irradiance, adequate gas precursors (e.g., NO x ), and lower temperaturewere observed at SHT, favorable for both photochemical production andgas-to-particle partitioning. This was further demonstrated by thesignificant increasing rate of oxygenated organic aerosols and NO 3 observed at SHT during 08:00–12:00 in spring (7.4 % h −1 and 12.9 % h −1 ) , fall (9.3 % h −1 and 9.1 % h −1 ) , and summer (13.0 % h −1 and 11.4 % h −1 ) , which cannot be fully explained byvertical mixing. It was noted that extremely high NO 3 was observed atSHT both in daytime and nighttime in winter, accounting for 37.2 % inNR-PM 1 , suggesting the efficient pathway from heterogeneous and gasoxidation formation. Therefore, we highlight the priority of NO x reduction inShanghai for the further improvement of air quality. This study reportedgreater daytime PM 2.5 concentrations at the height of 600 m in the urbanPBL compared with surface measurement, providing insight into theirpotential effects on local air quality, radiation forcing, and cloud and/or fogformations. We propose that the efficient production of secondary aerosol in themid-upper PBL should be cognized and explored more comprehensively bysynergetic observations in future.

[学科分类] 医学（综合）