Role of ambient ammonia in particulate ammonium formation at a rural site in the North China Plain
The real-time measurements of NH<sub>3</sub> and trace gases were conducted, in conjunction with semi-continuous measurements of water-soluble ions in PM<sub>2.5</sub> at a rural site in the North China Plain (NCP) from May to September 2013 in order to better understand c...
| Main Authors: | , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-01-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/18/167/2018/acp-18-167-2018.pdf |
| Summary: | The real-time measurements of NH<sub>3</sub> and trace gases were conducted, in
conjunction with semi-continuous measurements of water-soluble ions in
PM<sub>2.5</sub> at a rural site in the North China Plain (NCP) from May to
September 2013 in order to better understand chemical characteristics of
ammonia and the impact of secondary ammonium aerosols on formation in the
NCP. Extremely high NH<sub>3</sub> and NH<sub>4</sub><sup>+</sup> concentrations were observed
after a precipitation event within 7–10 days following urea application.
Elevated NH<sub>3</sub> levels coincided with elevated NH<sub>4</sub><sup>+</sup>,
indicating that NH<sub>3</sub> likely influenced particulate ammonium mass. For the
sampling period, the average conversion ∕ oxidation ratios for NH<sub>4</sub><sup>+</sup> (NHR), SO<sub>4</sub><sup>2−</sup> (SOR), and NO<sub>3</sub><sup>−</sup> (NOR) were estimated to be
0.30, 0.64, and 0.24, respectively. The increased NH<sub>3</sub> concentrations,
mainly from agricultural activities and regional transport, coincided with
the prevailing meteorological conditions. The high NH<sub>3</sub> level with NHR of
about 0.30 indicates that the emission of NH<sub>3</sub> in the NCP is much higher
than needed for aerosol acid neutralisation, and NH<sub>3</sub> plays an important
role in the formation of secondary aerosols as a key neutraliser. The hourly
data obtained were used to investigate gas–aerosol partitioning
characteristics using the thermodynamic equilibrium model ISORROPIA-II.
Modelled SO<sub>4</sub><sup>2−</sup>, NO<sub>3</sub><sup>−</sup>, and NH<sub>3</sub> values agree well with
the measurements, while the modelled NH<sub>4</sub><sup>+</sup> values largely underestimate the
measurements. Our observation and modelling results indicate that strong
acids in aerosol are completely neutralised. Additional NH<sub>4</sub><sup>+</sup> exists
in aerosol, probably a result of the presence of a substantial amount of oxalic and
other diacids. |
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| ISSN: | 1680-7316 1680-7324 |