Abstract. The atmospheric processes under polluted environments involving interactions of anthropogenic pollutants and natural emissions lead to the formation of various and complex secondary products. Therefore, the characterization of oxygenated organic compounds in urban areas remains a pivotal issue in our understanding of the evolution of organic carbon. Here, we describe measurements of an iodide chemical ionization
time-of-flight mass spectrometer installed with a Filter Inlet for Gases and
AEROsols (FIGAERO-I-CIMS) in both the gas phase and the particle phase at an urban
site in Guangzhou, a typical megacity in southern China, during the autumn
of 2018. Abundant oxygenated organic compounds containing two to five oxygen atoms
were observed, including organic acids, multi-functional organic compounds
typically emitted from biomass burning, oxidation products of biogenic
hydrocarbons and aromatics. Photochemistry played dominant roles in the
formation of gaseous organic acids and isoprene-derived organic nitrates,
while nighttime chemistry contributed significantly to the formation of
monoterpene-derived organic nitrates and inorganics. Nitrogen-containing
organic compounds occupied a significant fraction of the total signal in
both the gas and particle phases, with elevated fractions at higher
molecular weights. Measurements of organic compounds in the particle phase
by FIGAERO-I-CIMS explained 24 ± 0.8 % of the total organic aerosol
mass measured by aerosol mass spectrometer (AMS), and the fraction increased
for more aged organic aerosol. The systematical interpretation of mass
spectra of the FIGAERO-I-CIMS in the urban area of Guangzhou provides a
holistic view of numerous oxygenated organic compounds in the urban
atmosphere, which can serve as a reference for the future field measurements
by FIGAERO-I-CIMS in polluted urban regions.
Abstract. Ambient nitrate has been of increasing concern in
PM2.5, while there are still large uncertainties in quantifying the
formation of nitrate aerosol. The formation pathways of nitrate aerosol at
an urban site and a suburban site in the Pearl River Delta (PRD) are
investigated using an observation-constrained box model. Throughout the
campaigns, aerosol pollution episodes were constantly accompanied with the
increase in nitrate concentrations and fractions at both urban and suburban
sites. The simulations demonstrate that chemical reactions in the daytime
and at night both contributed significantly to formation of nitrate in the
boundary layer at the two sites. However, nighttime reactions predominantly
occurred aloft in the residual layer at the urban site, and downward
transport from the residual layer in the morning is an important source
(53 %) for surface nitrate at the urban site, whereas similar amounts of
nitrate were produced in the nocturnal boundary layer and residual layer at
the suburban site, which results in little downward transport of nitrate
from the residual layer to the ground at the suburban site. We show that
nitrate formation was in the volatile-organic-compound-limited (VOC-limited)
regime at the urban site, and in the transition regime at the suburban site,
identical to the response of ozone at both sites. The reduction of VOC
emissions can be an efficient approach to mitigate nitrate in both urban and
suburban areas through influencing hydroxyl radical (OH) and N2O5
production, which will also be beneficial for the synergistic control of
regional ozone pollution. The results highlight that the relative importance
of nitrate formation pathways and ozone can be site-specific, and the
quantitative understanding of various pathways of nitrate formation will
provide insights for developing nitrate and ozone mitigation strategies.
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