Strong anthropogenic control of secondary organic aerosol formation from isoprene in Beijing
<p>Isoprene-derived secondary organic aerosol (iSOA) is a significant contributor to organic carbon (OC) in some forested regions, such as tropical rainforests and the Southeastern US. However, its contribution to organic aerosol in urban areas that have high levels of anthropogenic pollutants...
| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-06-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/20/7531/2020/acp-20-7531-2020.pdf |
| Summary: | <p>Isoprene-derived secondary organic aerosol (iSOA) is a significant
contributor to organic carbon (OC) in some forested regions, such as
tropical rainforests and the Southeastern US. However, its contribution to
organic aerosol in urban areas that have high levels of anthropogenic
pollutants is poorly understood. In this study, we examined the formation of
anthropogenically influenced iSOA during summer in Beijing, China. Local
isoprene emissions and high levels of anthropogenic pollutants, in
particular <span class="inline-formula">NO<sub><i>x</i></sub></span> and particulate <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M2" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">SO</mi><mn mathvariant="normal">4</mn><mrow><mn mathvariant="normal">2</mn><mo>-</mo></mrow></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="29pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="74b4be02f6bf1e477b176a208786a61b"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-20-7531-2020-ie00001.svg" width="29pt" height="17pt" src="acp-20-7531-2020-ie00001.png"/></svg:svg></span></span>, led to the formation of
iSOA under both high- and low-NO oxidation conditions, with significant
heterogeneous transformations of isoprene-derived oxidation products to
particulate organosulfates (OSs) and nitrooxy-organosulfates (NOSs).
Ultra-high-performance liquid chromatography coupled to high-resolution mass
spectrometry was combined with a rapid automated data processing technique
to quantify 31 proposed iSOA tracers in offline PM<span class="inline-formula"><sub>2.5</sub></span> filter
extracts. The co-elution of the inorganic ions in the<span id="page7532"/> extracts caused matrix
effects that impacted two authentic standards differently. The average
concentration of iSOA OSs and NOSs was 82.5 ng m<span class="inline-formula"><sup>−3</sup></span>, which was around 3 times
higher than the observed concentrations of their oxygenated precursors
(2-methyltetrols and 2-methylglyceric acid). OS formation was dependant on
both photochemistry and the sulfate available for reactive uptake, as shown by a
strong correlation with the product of ozone (<span class="inline-formula">O<sub>3</sub></span>) and particulate
sulfate (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M6" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">SO</mi><mn mathvariant="normal">4</mn><mrow><mn mathvariant="normal">2</mn><mo>-</mo></mrow></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="29pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="a8455a3a3390243c17ea2f3ca419ac4e"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-20-7531-2020-ie00002.svg" width="29pt" height="17pt" src="acp-20-7531-2020-ie00002.png"/></svg:svg></span></span>). A greater proportion of high-NO OS products were
observed in Beijing compared with previous studies in less polluted
environments. The iSOA-derived OSs and NOSs represented 0.62 %
of the oxidized organic aerosol measured by aerosol mass spectrometry on average, but
this increased to <span class="inline-formula">∼3 <i>%</i></span> on certain days. These results
indicate for the first time that iSOA formation in urban Beijing is strongly
controlled by anthropogenic emissions and results in extensive conversion to
OS products from heterogenous reactions.</p> |
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| ISSN: | 1680-7316 1680-7324 |