Formation of light-absorbing carbon aerosols from biogenic isoprene intermediates (2014)

Undergraduates: Kevin Chu, Ying-Hsuan Lin, Sari Budisulistiorini

Faculty Advisor: Jason Surratt
Department: Environmental Science

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Light-absorbing organic carbon is an important climate warming agent that contributes to positive radiative forcing, but to date it is generally not represented in current climate models in part due to lack of understanding in its sources and formation processes. Secondary organic aerosol produced from heterogeneous reactive uptake of isoprene epoxydiols has been found to substantially contribute to the organic aerosol mass over the Southeast U.S. where SOA formation from isoprene is significantly enhanced by biogenic/anthropogenic interactions. Brown carbon in rural areas in this region has been reported to be associated with secondary sources in summer when influences from biomass burning are low. Chemical analyses of light-absorbing SOA constituents using diode array detection and mass spectrometric techniques indicate the formation of Isoprene-derived Brown Carbon is strongly associated with 3-methyltetrahydrofuran-3,4-diols, which are products of acid-catalyzed intramolecular rearrangement of isoprene-epoxydiols in the particle phase. Field observations of these conjugated oligomers from the rural southeast U.S. support the atmospheric relevance of this secondary Brown Carbon source. These results illustrate a previously unknown relationship between isoprene, the second most abundant atmospheric hydrocarbon, and the radiative budget with major implications for air quality and climate models.