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Formation of anthropogenic secondary organic aerosol (SOA) and its influence on biogenic SOA properties

Artikel i vetenskaplig tidskrift
Författare Eva U. Emanuelsson
Mattias Hallquist
K. Kristensen
M. Glasius
B. Bohn
H. Fuchs
B. Kammer
A. Kiendler-Scharr
S. Nehr
F. Rubach
R. Tillmann
A. Wahner
H. C. Wu
Th F. Mentel
Publicerad i Atmospheric Chemistry and Physics Discussions
Volym 12
Nummer/häfte 8
Sidor 20311-20350
ISSN 1680-7367
Förlag Copernicus Publications
Publiceringsår 2012
Publicerad vid Institutionen för kemi och molekylärbiologi
Sidor 20311-20350
Språk en
Länkar dx.doi.org/10.5194/acpd-12-20311-20...
Ämneskategorier Kemi, Analytisk kemi, Fysikalisk kemi, Klimatforskning, Miljövetenskap, Miljökemi

Sammanfattning

Secondary organic aerosol (SOA) formation from mixed anthropogenic and biogenic precursors has been studied exposing reaction mixtures to natural sunlight in the SAPHIR chamber in Jülich, Germany. Several experiments with exclusively anthro- 5 pogenic precursors were performed to establish a relationship between yield and organic aerosol mass loading for the atmospheric relevant range of aerosol loads of 0.01 to 10 μgm−3. The yields (0.5–9 %) were comparable to previous data and further used for the detailed evaluation of the mixed biogenic and anthropogenic experiments. For the mixed experiments a number of different oxidation schemes were addressed. The 10 reactivity, the sequence of addition, and the amount of the precursors influenced the SOA properties. Monoterpene oxidation products, including carboxylic acids and dimer esters were identified in the aged aerosol at levels comparable to ambient air. OH radicals were measured by Laser Induced Fluorescence, which allowed for establishing relations of aerosol properties and composition to the experimental OH dose. Further 15 more, the OH measurements in combination with the derived yields for anthropogenic SOA enabled application of a simplified model to calculate the chemical turnover of the anthropogenic precursor and corresponding anthropogenic contribution to the mixed aerosol. The estimated anthropogenic contributions were ranging from small (8 %) up to significant fraction (>50 %) providing a suitable range to study the effect of aerosol 20 composition on the aerosol volatility (volume fraction remaining at 343 K: 0.86–0.94). The anthropogenic aerosol had higher oxygen to carbon ratio O/C and was less volatile than the biogenic fraction. However, in order to produce significant amount of anthropogenic SOA the reaction mixtures needed a higher OH dose that also increased O/C and provided a less volatile aerosol. A strong positive correlation was found between 25 changes in volatility and O/C with the exception during dark hours where the SOA volatility decreased while O/C did not change significantly. This change in volatility under dark conditions is likely due to chemical or morphological changes not affecting O/C.

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