Production of N<sub>2</sub>O<sub>5</sub> and ClNO<sub>2</sub> in summer in urban Beijing, China
<p>The heterogeneous hydrolysis of dinitrogen pentoxide (N<sub>2</sub>O<sub>5</sub>) has a significant impact on both nocturnal particulate nitrate formation and photochemistry on the following day through the photolysis of nitryl chloride (ClNO<sub>2</sub&g...
| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-08-01
|
| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/18/11581/2018/acp-18-11581-2018.pdf |
| Summary: | <p>The heterogeneous hydrolysis of dinitrogen pentoxide
(N<sub>2</sub>O<sub>5</sub>) has a significant impact on both nocturnal particulate
nitrate formation and photochemistry on the following day through the photolysis
of nitryl chloride (ClNO<sub>2</sub>), yet these processes in highly polluted
urban areas remain poorly understood. Here we present measurements of
gas-phase N<sub>2</sub>O<sub>5</sub> and ClNO<sub>2</sub> by high-resolution time-of-flight
chemical ionization mass spectrometer (ToF-CIMS) during summer in urban
Beijing, China as part of the Air Pollution and Human Health (APHH)
campaign. N<sub>2</sub>O<sub>5</sub> and ClNO<sub>2</sub> show large day-to-day variations
with average (±1<i>σ</i>) mixing ratios of 79.2±157.1 and
174.3±262.0 pptv, respectively. High reactivity of N<sub>2</sub>O<sub>5</sub>,
with <i>τ</i> (N<sub>2</sub>O<sub>5</sub>)<sup>−1</sup> ranging from 0.20  ×  10<sup>−2</sup> to
1.46  ×  10<sup>−2</sup> s<sup>−1</sup>, suggests active nocturnal
chemistry and a large nocturnal nitrate formation potential via
N<sub>2</sub>O<sub>5</sub> heterogeneous uptake. The lifetime of N<sub>2</sub>O<sub>5</sub>, <i>τ</i> (N<sub>2</sub>O<sub>5</sub>),
decreases rapidly with the increase in aerosol surface
area, yet it varies differently as a function of relative humidity with the
highest value peaking at ∼  40 %. The N<sub>2</sub>O<sub>5</sub> uptake
coefficients estimated from the product formation rates of ClNO<sub>2</sub> and
particulate nitrate are in the range of 0.017–0.19, corresponding to direct
N<sub>2</sub>O<sub>5</sub> loss rates of 0.00044–0.0034 s<sup>−1</sup>. Further analysis
indicates that the fast N<sub>2</sub>O<sub>5</sub> loss in the nocturnal boundary layer
in urban Beijing is mainly attributed to its indirect
loss via NO<sub>3</sub>, for example through the reactions with volatile organic
compounds and NO, while the contribution of the heterogeneous uptake of
N<sub>2</sub>O<sub>5</sub> is comparably small (7–33 %). High ClNO<sub>2</sub> yields
ranging from 0.10 to 0.35 were also observed, which might have important
implications for air quality by affecting nitrate and ozone
formation.</p> |
|---|---|
| ISSN: | 1680-7316 1680-7324 |