Vertical Characterization of Aerosol Particle Composition in Beijing, China: Insights From 3‐Month Measurements With Two Aerosol Mass Spectrometers

Abstract

Despite extensive studies for characterization of aerosol chemistry near ground level, long‐term vertical characterization of aerosol particle composition in Beijing is very limited. In this work, non‐refractory submicron aerosol (NR‐PM1) species were simultaneously measured at ground level and 260 m on a meteorological tower from 14 October 2014 to 18 January 2015 in Beijing using two aerosol mass spectrometers. Our results showed overall lower concentrations of NR‐PM1 at 260 m by 2%–36% than ground level in both heating and non‐heating seasons, and also larger vertical gradients during clean periods than polluted episodes. The vertical ratios and correlations of aerosol species between ground level and 260 m presented higher values in daytime and lower ones at nighttime mainly due to the influences of planetary boundary layer and local source emissions, respectively. Nitrate showed ubiquitously higher ratio of 260 m to ground (ratio260m/ground) than sulfate due to a higher formation potential from gas‐particle partitioning and heterogeneous reactions at higher heights. A detailed analysis of vertical evolution showed relatively stable ratios260m/ground for secondary aerosol species during the early formation stage of haze episodes, which decreased simultaneously along with mixing layer height during the later severely polluted periods with NR‐PM1 concentration above 150 μg/m3. Our results demonstrated that the evolution of vertical differences in megacities is subject to the influences from both physical (e.g., regional transport, mountain‐valley winds, inversions of temperature and relative humidity, and mixing layer height) and chemical processes (e.g., gas‐particle partitioning and aqueous‐phase processing).

Measurement report: Comparison of wintertime individual particles at ground level and above the mixed layer in urban Beijing

“…As the megacity capital, Beijing has received much attention, being one of the most polluted cities in China. Atmospheric researchers have been studying aerosol particles to understand haze formation in China Huang et al, 2014;Zhou et al, 2018b). Measurements and model analyses highlight the key roles of secondary aerosol formation by trace gases (e.g., volatile organic compounds, SO 2 , and NO x ) and stagnant meteorological conditions in the regional haze formation (Wang et al, 2013;Guo et al, 2014;Huang et al, 2014).…”

“…Vertical differences between precursors, oxidants, and temperature gradients might influence gas-particle partitioning and heterogeneous reactions of N 2 O 5 (Zhou et al, 2018a). Previous measurements at the Institute of Atmospheric Physics (IAP) meteorological tower in Beijing showed complex vertical distributions of particulate matter and gaseous pollutants (Meng et al, 2008;Sun et al, 2015;Wang et al, 2018;Zhou et al, 2018b). However, most of these studies focused on non-refractory submicron species.…”

Spatial variability of air pollutants in a megacity characterized by mobile measurements: Chemical homogeneity under haze conditions

“…Tower measurements have shown greater vertical gradients of particulate matter (PM) concentration and composition during clean periods than haze periods in Beijing, which is attributed to the influence of both physical (e.g., regional transport, mixing layer height, and inversions etc.) and chemical processes (e.g., gas-particle partitioning and aqueous processing) (Zhou et al, 2018). Significant vertical gradients also present in the concentrations of VOCs in cities, which can be affected by transport of air mass, vertical diffusion, and species reactivity (Sun et al, 2018;Mo et al, 2020).…”

Measurement report: Comparison of wintertime individual particles at ground level and above the mixed layer in urban Beijing

“…As characterization of aerosol particles has focused on surface level observations, the knowledge of aerosol properties at higher altitudes in urban areas remains poor (Zhou et al, 2018a).…”

“…Vertical differences between precursors, oxidants and temperature gradients may influence gasparticle partitioning and heterogeneous reactions of N2O5 (Zhou et al, 2018a). Previous Beijing measurements at the Institute of Atmospheric Physics (IAP) meteorological tower showed complex vertical distributions of particulate matter and gaseous pollutants (Meng et al, 2008;Sun et al, 2015;Wang et al, 2018;Zhou et al, 2018b), but most of these studies focused on non-refractory submicron species.…”