Efficient N<sub>2</sub>O<sub>5</sub> uptake and NO<sub>3</sub> oxidation in the outflow of urban Beijing
<p>Nocturnal reactive nitrogen compounds play an important role in regional air pollution. Here we present the measurements of dinitrogen pentoxide (N<sub>2</sub>O<sub>5</sub>) associated with nitryl chloride (ClNO<sub>2</sub>) and particulate nitrate (&l...
| Main Authors: | , , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-07-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/18/9705/2018/acp-18-9705-2018.pdf |
| Summary: | <p>Nocturnal reactive nitrogen compounds play an important role in regional air
pollution. Here we present the measurements of dinitrogen pentoxide
(N<sub>2</sub>O<sub>5</sub>) associated with nitryl chloride (ClNO<sub>2</sub>) and particulate
nitrate (<i>p</i>NO<sub>3</sub><sup>−</sup>) at a suburban site of Beijing in the summer of 2016.
High levels of N<sub>2</sub>O<sub>5</sub> and ClNO<sub>2</sub> were observed in the
outflow of the urban Beijing air masses, with 1 min average maxima of 937 and 2900 pptv,
respectively. The N<sub>2</sub>O<sub>5</sub> uptake coefficients,
<i>γ</i>, and ClNO<sub>2</sub> yield, <i>f</i>, were experimentally determined
from the observed parameters. The N<sub>2</sub>O<sub>5</sub> uptake coefficient ranged
from 0.012 to 0.055, with an average of 0.034 ± 0.018, which is in the
upper range of previous field studies reported in North America and Europe
but is a moderate value in the North China Plain (NCP), which reflects
efficient N<sub>2</sub>O<sub>5</sub> heterogeneous processes in Beijing. The
ClNO<sub>2</sub> yield exhibited high variability, with a range of 0.50 to
unity and an average of 0.73 ± 0.25. The concentration of the nitrate
radical (NO<sub>3</sub>) was calculated assuming that the thermal equilibrium
between NO<sub>3</sub> and N<sub>2</sub>O<sub>5</sub> was maintained. In
NO<sub><i>x</i></sub>-rich air masses, the oxidation of nocturnal biogenic
volatile organic compounds (BVOCs) was dominated by NO<sub>3</sub> rather than
O<sub>3</sub>. The production rate of organic nitrate (ON) via NO<sub>3</sub> + BVOCs was
significant, with an average of 0.10 ± 0.07 ppbv h<sup>−1</sup>. We highlight
the importance of NO<sub>3</sub> oxidation of VOCs in the formation of ON and
subsequent secondary organic aerosols in summer in Beijing.</p> |
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| ISSN: | 1680-7316 1680-7324 |