Characteristics and sources of submicron aerosols above the urban canopy (260 m) in Beijing, China during 2014 APEC summit

Abstract

Abstract. The megacity of Beijing has experienced frequent severe fine particle pollution during the last decade. Although the sources and formation mechanisms of aerosol particles have been extensively investigated on the basis of ground measurements, real-time characterization of aerosol particle composition and sources above the urban canopy in Beijing is rare. In this study, we conducted real-time measurements of non-refractory submicron aerosol (NR-PM1) composition at 260 m at the 325 m Beijing Meteorological Tower (BMT) from 10 October to 12 November 2014, by using an aerosol chemical speciation monitor (ACSM) along with synchronous measurements of size-resolved NR-PM1 composition at near ground level using a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR–ToF–AMS). The NR-PM1 composition above the urban canopy was dominated by organics (46 %), followed by nitrate (27 %) and sulfate (13 %). The high contribution of nitrate and high NO3−/SO42− mass ratios illustrate an important role of nitrate in particulate matter (PM) pollution during the study period. The organic aerosol (OA) was mainly composed by secondary OA (SOA), accounting for 61 % on an average. Different from that measured at the ground site, primary OA (POA) correlated moderately with SOA, likely suggesting a high contribution from regional transport above the urban canopy. The Asia–Pacific Economic Cooperation (APEC) summit with strict emission controls provides a unique opportunity to study the impacts of emission controls on aerosol chemistry. All aerosol species were shown to have significant decreases of 40–80 % during APEC from those measured before APEC, suggesting that emission controls over regional scales substantially reduced PM levels. However, the bulk aerosol composition was relatively similar before and during APEC as a result of synergetic controls of aerosol precursors such as SO2, NOx, and volatile organic compounds (VOCs). In addition to emission controls, the routine circulations of mountain–valley breezes were also found to play an important role in alleviating PM levels and achieving the "APEC blue" effect. The evolution of vertical differences between 260 m and the ground level was also investigated. Our results show complex vertical differences during the formation and evolution of severe haze episodes that are closely related to aerosol sources and boundary layer dynamics.

Characterization of Chemical Composition in PM2.5 in Beijing before, during, and after a Large-Scale International Event

“…However, when the wind direction changed from the south to the north, the concentration of PM 2.5 rapidly decreased. Haze episodes with such cycle driven by meteorological conditions have also been observed many times in Beijing Chen et al, 2015). A highly negative correlation was found between PM 2.5 concentration and visibility, with a correlation coefficient of -0.77.…”

Variation of Bacterial and Fungal Community Structures in PM2.5 Collected during the 2014 APEC Summit Periods

“…The high similarity between AD-GD and AN-GN demonstrated that the emission control measures implemented during the summit had little effect on the bacterial community structure. Chen et al (2015) suggested the aerosol chemical composition pattern was relatively similar before and during APEC summit although various aerosol pollutants decreased significantly by 40%-80% following the emission control measures. Furthermore, the similarities of GD-MD, GD-HD, and MD-HD were more than 84.2%, 82.3%, and 78.9%, respectively.…”

“…Beijing, an international megacity, has been suffering from serious PM 2.5 (aerosol particles with an aerodynamic diameter of ≤ 2.5 µm) pollution (Xu et al, 2005;Zhou et al, 2015;Lang et al, 2017). Although previous studies have shown that the annual average concentration of PM 2.5 in some cities in China was more than 90 µg m -3 (He et al, 2001;Zheng et al, 2005;Meng et al, 2007;Feng et al, 2009), public awareness regarding PM 2.5 was low until 2011.…”

Evaluating the Effects of Springtime Dust Storms over Beijing and the Associated Characteristics of Sub-Micron Aerosol

“…In particular, based on the high resolution characteristics of the HR-ToF-AMS, multiple organic aerosol (OA) sources have be identified and recognized by combining the positive matrix factorization (PMF) model with the high-resolution OA mass spectral matrix (Ulbrichet al, 2009). Although many studies have been conducted in Beijing to evaluate the composition of submicron particles using HR-ToF-AMS, these observations have mainly been carried out in the summer, autumn and winter Sun et al, 2013b;Zhang et al, 2014;Chen et al, 2015;Xu et al, 2015;Zhang et al, 2016). Although Sun et al (2015) used Aerosol Chemical Speciation Monitors (ACSM) to analyze the variation of submicron particles in spring, the elemental composition and source apportionment of the organic aerosol were not studied.…”