Tracking anthropogenic influence on isoprene chemistry over Amazonia
Monday, 15 December 2014: 2:40 PM
Primarily emitted by vegetation, isoprene is the dominant nonmethane hydrocarbon in the atmosphere. Photooxidation of isoprene has a large influence on the oxidation capacity of the atmosphere and the production of secondary organic aerosol (SOA). As a part of the GoAmazon2014 Experiment, isoprene and some of its oxidation products were measured using a proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF-MS) at a research site 60 km west of the city of Manaus, Brazil. The fetch of the research site oscillated between the extremes of a pristine atmosphere and the interactions of heavy pollution from Manaus with the natural environment, which allowed for an assessment of the modifications of natural isoprene chemistry by anthropogenic pollution over Amazonia. Photooxidation of isoprene leads to chemically different oxidation products depending on the fate of isoprene peroxy radicals (ISOPOO), but different oxidation products can produce the same ions in PTR-MS analysis due to similarity in their chemical structures. A cold trap was deployed in front of the PTR-TOF-MS for separation and differential classification of some of these isoprene oxidation products. For example, isoprene-derived hydroperoxides (C5H10O3) and methyl vinyl ketone/methacrolein (C4H6O), which are the major oxidation products of the HO2 and NO pathways of ISOPOO reaction, respectively, and both detected as C4H7O+ ion by PTR-MS, were separately measured. Using the measurements of these and other oxidation products of isoprene by PTR-TOF-MS and other complementary measurements, the isoprene chemistry (particularly the fate of ISOPOO) under pristine and polluted scenarios are compared and the implication for SOA formation is discussed.