 |
| Titel |
The influence of semi-volatile and reactive primary emissions on the abundance and properties of global organic aerosol |
| VerfasserIn |
S. H. Jathar, S. C. Farina, A. L. Robinson, P. J. Adams |
| Konferenz |
EGU General Assembly 2012
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250063374
|
|
|
|
|
|
| Zusammenfassung |
| Semi-volatile and reactive primary organic aerosols are modeled on a global scale using the
GISS GCM II’ “unified" climate model. We employ the volatility basis set framework to
simulate emissions, chemical reactions and phase partitioning of primary and secondary
organic aerosol (POA and SOA). The model also incorporates the emissions and reactions of
intermediate volatility organic compounds (IVOCs) as a source of organic aerosol (OA), one
that has been missing in most prior work. Model predictions are evaluated against a
broad set of observational constraints including mass concentrations, degree of
oxygenation, volatility and isotopic composition. A traditional model that treats POA
as non-volatile and non-reactive is also compared to the same set of observations
to highlight the progress made in this effort. The revised model predicts a global
dominance of SOA and brings the POA/SOA split into better agreement with ambient
measurements. This change is due to traditionally defined POA evaporating and the
evaporated vapors oxidizing to form non-traditional SOA. IVOCs (traditionally not
included in chemical transport models) oxidize to form condensable products that
account for a third of total OA, suggesting that global models have been missing a
large source of OA. Predictions of the revised model for the SOA fraction at 17
different locations compared much better to observations than predictions from
the traditional model. Model-predicted volatility is compared with thermodenuder
data collected at three different field campaigns: FAME-2008, MILAGRO-2006
and SOAR-2005. The revised model predicts the OA volatility much more closely
than the traditional model. When compared against monthly averaged OA mass
concentrations measured by the IMPROVE network, predictions of both the revised and
traditional model lie within a factor of two in summer and mostly within a factor of five
during winter. A sensitivity analysis indicates that the winter comparison can be
improved either by increasing POA emissions or lowering the volatility of those
emissions. Model predictions of the isotopic composition of OA are compared
against those computed via a radiocarbon isotope analysis of field samples. The
contemporary fraction, on average, is slightly under-predicted (20%) during the summer
months but is a factor of two lower during the winter months. We hypothesize that
the large wintertime under-prediction of surface OA mass concentrations and the
contemporary fraction is due to an under-representation of biofuel (particularly,
residential wood burning) emissions in the emission inventory. Overall, the model
evaluation highlights the importance of treating POA as semi-volatile and reactive in
order to predict accurately the sources, composition and properties of ambient OA. |
|
|
|
|
|
|