Nitro-polycyclic aromatic hydrocarbons – gas–particle partitioning, mass size distribution, and formation along transport in marine and continental background air
Nitro-polycyclic aromatic hydrocarbons (NPAH) are ubiquitous in polluted air but little is known about their abundance in background air. NPAHs were studied at one marine and one continental background site, i.e. a coastal site in the southern Aegean Sea (summer 2012) and a site in the central Great...
| Main Authors: | , , , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-05-01
|
| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/17/6257/2017/acp-17-6257-2017.pdf |
| Summary: | Nitro-polycyclic aromatic hydrocarbons (NPAH) are ubiquitous in
polluted air but little is known about their abundance in background air.
NPAHs were studied at one marine and one continental background site, i.e. a
coastal site in the southern Aegean Sea (summer 2012) and a site in the
central Great Hungarian Plain (summer 2013), together with the parent
compounds, PAHs. A Lagrangian particle dispersion model was used to track air
mass history. Based on Lagrangian particle statistics, the urban influence on
samples was quantified for the first time as a fractional dose to which the
collected volume of air had been exposed.
<br><br>
At the remote marine site, the 3–4-ring NPAH (sum of 11 targeted species)
concentration was 23.7 pg m<sup>−3</sup> while the concentration of 4-ring PAHs (6
species) was 426 pg m<sup>−3</sup>. The most abundant NPAHs were 2-nitrofluoranthene (2NFLT) and
3-nitrophenanthrene. Urban fractional doses in
the range of < 0.002–5.4 % were calculated. At the continental site,
the Σ<sub>11</sub> 3–4-ring NPAH and Σ<sub>6</sub> 4-ring PAH were 58 and 663 pg m<sup>−3</sup>,
respectively, with 9-nitroanthracene and 2NFLT being the most
concentrated amongst the targeted NPAHs. The NPAH levels observed in the
marine background air are the lowest ever reported and remarkably lower, by more
than 1 order of magnitude, than 1 decade before. Day–night variation of
NPAHs at the continental site reflected shorter lifetime during the day,
possibly because of photolysis of some NPAHs. The yields of formation of
2NFLT and 2-nitropyrene (2NPYR) in marine air seem to be close to the yields
for OH-initiated photochemistry observed in laboratory experiments under
high NO<sub><i>x</i></sub> conditions. Good agreement is found for the prediction of NPAH
gas–particle partitioning using a multi-phase poly-parameter linear free-energy relationship. Sorption to soot is found to be less significant for
gas–particle partitioning of NPAHs than for PAHs. The NPAH levels determined
in the south-eastern outflow of Europe confirm intercontinental transport
potential. |
|---|---|
| ISSN: | 1680-7316 1680-7324 |