Stable carbon isotope ratios of ambient aromatic volatile organic compounds
Measurements of mixing ratios and stable carbon isotope ratios of aromatic volatile organic compounds (VOC) in the atmosphere were made in Toronto (Canada) in 2009 and 2010. Consistent with the kinetic isotope effect for reactions of aromatic VOC with the OH radical the observed stable carbon is...
| Main Authors: | , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-09-01
|
| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/16/11755/2016/acp-16-11755-2016.pdf |
| Summary: | Measurements of mixing ratios and stable carbon isotope ratios of
aromatic volatile organic compounds (VOC) in the atmosphere were made in
Toronto (Canada) in 2009 and 2010. Consistent with the kinetic isotope
effect for reactions of aromatic VOC with the OH radical the observed stable
carbon isotope ratios are on average significantly heavier than the isotope
ratios of their emissions. The change of carbon isotope ratio between
emission and observation is used to determine the extent of photochemical
processing (photochemical age, <mo form="infix">∫</mo> [OH]d<i>t</i>) of the different VOC. It is
found that <mo form="infix">∫</mo> [OH]d<i>t</i> of different VOC depends strongly on the VOC
reactivity. This demonstrates that for this set of observations the
assumption of a uniform <mo form="infix">∫</mo> [OH]d<i>t</i> for VOC with different reactivity
is not justified and that the observed values for <mo form="infix">∫</mo> [OH]d<i>t</i> are the
result of mixing of VOC from air masses with different values for <mo form="infix">∫</mo> [OH]d<i>t</i>. Based on comparison between carbon isotope ratios and VOC
concentration ratios it is also found that the varying influence of sources with
different VOC emission ratios has a larger impact on VOC concentration
ratios than photochemical processing. It is concluded that for this data set
the use of VOC concentration ratios to determine <mo form="infix">∫</mo> [OH]d<i>t</i> would
result in values for <mo form="infix">∫</mo> [OH]d<i>t</i> inconsistent with carbon isotope
ratios and that the concept of a uniform <mo form="infix">∫</mo> [OH]d<i>t</i> for an air mass
has to be replaced by the concept of individual values of an average
<mo form="infix">∫</mo> [OH]d<i>t</i> for VOC with different reactivity.</p> |
|---|---|
| ISSN: | 1680-7316 1680-7324 |