The formation mechanism of aerosol sulfate during wintertime haze events in China is still largely unknown. As companions, SO2 and transition metals are mainly emitted from coal combustion. Here, we argue that the transition metal-catalyzed oxidation of SO2 on aerosol surfaces could be the dominant sulfate formation pathway and investigate this hypothesis by integrating chamber experiments, numerical simulations and in-field observations. Our analysis shows that the contribution of the manganese-catalyzed oxidation of SO2 on aerosol surfaces is approximately one to two orders of magnitude larger than previously known routes, and contributes 69.2% ± 5.0% of the particulate sulfur production during haze events. This formation pathway could explain the missing source of sulfate and improve the understanding of atmospheric chemistry and climate change.
Abstract. Secondary aerosols are a major component of PM2.5, yet their formation
mechanisms in the ambient atmosphere are still unclear. Based on field
measurements in downtown Beijing, we show that the photolysis of nitrous
acid (HONO) may promote the formation of organic and nitrate aerosols in
winter in Beijing, which is supported by the fact that the mass
concentrations of organic and nitrate aerosols linearly increase as a
function of HONO consumed from early morning to noon. The increased nitrate
content also leads to the formation of ammonium particulate matter through
enhancing the neutralization of nitrate and sulfate by ammonia. We further
illustrate that during pollution events in winter in Beijing, over 50 %
of the ambient HONO may be related to traffic-related emissions, including
direct emissions and formation via the reaction between OH and
vehicle-emitted NO. Overall, our results indicate that traffic-related HONO
may play an important role in the oxidative capacity and in turn contribute
to haze formation in winter in Beijing. The mitigation of HONO and NOx
emissions from vehicles may be an effective way to reduce the formation of
secondary aerosols and severe haze events in winter in Beijing.
Long-chain alkanes are a type of intermediate volatility organic compound (IVOC) in the atmosphere and a potential source of secondary organic aerosols (SOAs). C 12 −C 14 nalkylcyclohexanes are important compositions of IVOCs, with considerable concentrations and emission rates. The reaction rate constants and SOA formation of the reactions of C 12 −C 14 nalkylcyclohexanes with Cl atoms were investigated in the present study. The reaction rate constants of the long-chain alkanes obtained via the relative-rate method at 298 ± 0.2 K (in units of ×10 −10 cm 3 molecule −1 s −1 ) were as follows: k hexylcyclohexane = 5.11 ± 0.28, k heptylcyclohexane = 5.56 ± 0.30, and k octylcyclohexane = 5.74 ± 0.31. The gas-phase products of the reactions were identified as mainly small molecules of aldehydes, ketones, and acids. The particlephase products were mostly monomers and oligomers, but there were still trimers even under high-NO x conditions. Moreover, under high-NO x conditions (urban atmosphere), the SOA yields of hexylcyclohexane are higher than that under low-NO x conditions (remote atmosphere), indicating that more attention should be given to the SOA formation of Cl-initiated n-alkylcyclohexane oxidations in polluted regions. This research can further clarify the oxidation processes and SOA formation of n-alkylcyclohexanes in the atmosphere.
The optimal storage temperature for vaccines ranges from 2 to 8 °C. Electronic thermometers is able to provide real-time and remote temperature monitoring, but cannot applied to individual package. As...
Abstract. Co-occurrences of high concentrations of PM2.5 and ozone (O3) have
been frequently observed in haze-aggravating processes in the North China
Plain (NCP) over the past few years. Higher O3 concentrations on hazy
days were hypothesized to be related to nitrous acid (HONO), but the key sources
of HONO enhancing O3 during haze-aggravating processes remain unclear.
We added six potential HONO sources, i.e., four ground-based (traffic, soil,
and indoor emissions, and the NO2 heterogeneous reaction on ground
surface (Hetground)) sources, and two aerosol-related (the NO2
heterogeneous reaction on aerosol surfaces (Hetaerosol) and nitrate
photolysis (Photnitrate)) sources into the WRF-Chem model and designed
23 simulation scenarios to explore the unclear key sources. The results
indicate that ground-based HONO sources producing HONO enhancements showed a
rapid decrease with height, while the NO + OH reaction and aerosol-related
HONO sources decreased slowly with height. Photnitrate contributions to
HONO concentrations were enhanced with aggravated pollution levels. The enhancement of
HONO due to Photnitrate on hazy days was about 10 times greater than on
clean days and Photnitrate dominated daytime HONO sources
(∼ 30 %–70 % when the ratio of the photolysis frequency of
nitrate (Jnitrate) to gas nitric acid (JHNO3) equals 30) at higher
layers (>800 m). Compared with that on clean days, the
Photnitrate contribution to the enhanced daily maximum 8 h averaged
(DMA8) O3 was increased by over 1 magnitude during the haze-aggravating process. Photnitrate contributed only ∼ 5 %
of the surface HONO in the daytime with a Jnitrate/JHNO3 ratio of 30
but contributed ∼ 30 %–50 % of the enhanced O3 near the
surface in NCP on hazy days. Surface O3 was dominated by volatile
organic compound-sensitive chemistry, while O3 at higher altitudes
(>800 m) was dominated by NOx-sensitive chemistry.
Photnitrate had a limited impact on nitrate concentrations (<15 %) even with a Jnitrate/JHNO3 ratio of 120. These results
suggest the potential but significant impact of Photnitrate on O3
formation, and that more comprehensive studies on Photnitrate in the
atmosphere are still needed.
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