 |
| Titel |
BrO loss due to secondary organic aerosols |
| VerfasserIn |
Joelle Buxmann, Sergej Bleicher, Cornelius Zetzsch, Andreas Held, Roberto Sommariva, Roland von Glasow, Ulrich Platt, Johannes Ofner |
| Konferenz |
EGU General Assembly 2013
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250077024
|
|
|
|
|
|
| Zusammenfassung |
| One major source of heterogeneous released reactive halogen species (RHS) is primary
aerosol from sea-salt particles, ejected by sea spray. Photoactivated RHS emissions, such as
atomic Br and BrO radicals, can play a key role in the destruction of atmospheric ozone,
influencing HOx and NOx chemistry. Through aerosol interaction they show potential
indirect effects on global climate.
The formation of RHS can be significantly reduced in the presence of organic aerosols.
Additionally, halogen species were found to change the aerosol size distribution, the presence
of functional groups and the optical properties. Furthermore, they may form halogenated
species in the condensed phase of the organic aerosol - although the inhibition of the
formation of RHS has not been quantified before. The interaction of secondary organic
aerosols (SOA) from predominantly aliphatic (α-pinene) or aromatic (catechol and guaiacol)
precursors and heterogeneously released halogens was studied in smog-chamber experiments.
BrO and OClO released from salt aerosols were detected by a White system in combination
with Differential Optical Absorption Spectroscopy (DOAS). The size and number distribution
of aerosols from salt droplets (~150nm-1000nm) and from SOA (~5nm-150nm) was
quantified by a SMPS (Scanning Mobility Particle Sizer) to obtain typical surface areas of
103μm2/cm3 and 2 x 102μm2/cm3, respectively. In the absence of SOA a BrO production
rate per salt aerosol surface area of 5.2 x 1011 molec/cm2s =8500 pmol/m2s has
been measured. This confirms model assumptions for BrO formation over the Dead
Sea, where the Br2 flux of 80-154 pmol/m2s and HOBr flux= 800 pmol/m2s was
increased by a factor of 20-30 to explain high BrO mixing ratios. In the presence of
SOA from α-pinene, catechol and guaiacol the formation rate was significantly
reduced. In a first approximation, neglecting gas phase reactions, the BrO loss rate
regarding the surface area of SOA was calculated to be 42 x 1011 molec/cm2s, 12 x
1011molec/cm2sand 10 x 1011molec/cm2 s for α-pinene, catechol and guaiacol,
respectively. In the presence of SOA about 150 ppt of OClO were formed, which is not
completely understood yet, but acidification by organic acids might trigger a chlorine
release.
Model studies of the experiments including gas and particulate phase reactions will be
presented in order to help explain reaction pathways and to estimate accommodation
coefficients. In conclusion, we found a reduced formation of BrO in the presence of SOA, and
therefore less Br-catalysed O3 destruction. We also show the first quantitative BrO loss rate
due to SOA, where α-pinene shows 4 times higher loss rate compared to catechol and
guaiacol. |
|
|
|
|
|
|