GOAMAZON-SVTAG

Observations and Modeling of the Green Ocean Amazon: Semi-Volatile Thermal desorption Aerosol Gas chromatograph (SVTAG)

1 February 2014 - 15 October 2014

Lead Scientist: Allen Goldstein

Observatory: AMF , MAO

In areas where biogenic emissions are oxidized in the presence of anthropogenic pollutants such as SO2, NOx and black carbon, it has become increasingly apparent that secondary organic aerosol (SOA) formation from biogenic volatile organic compounds (VOCs) is substantially enhanced. Research is urgently needed to elucidate fundamental processes of natural and anthropogenically-influenced VOC oxidation and the contribution of these processes to SOA formation. GoAmazon 2014 affords study of the chemical transformations in the region downwind of Manaus where local biogenic VOC emissions are high, and their chemical oxidation can be studied both inside and outside of the urban plume to differentiate the role of anthropogenic influence on secondary aerosol formation during oxidation of these natural VOC emissions. To understand the connection between primary biogenic VOC emissions and their secondary products that form aerosols, we made time-resolved molecular level measurements by deploying a Semi-Volatile Thermal desorption Aerosol Gas Chromatograph (SV-TAG) and a sequential filter sampler during two intensive operating periods (IOPs) of the GoAmazon field campaign. The SV-TAG measured semi-volatile organic compounds in both the gas and particle phases and the sequential filter sampler collected aerosols on quartz fiber filters in four hour increments used for off-line analysis. SV-TAG employed novel on-line derivatization that provided chemical speciation of highly oxygenated or functionalized compounds that comprise a substantial fraction of secondary organic aerosols, yet are poorly characterized. It also provided partitioning of these compounds between the vapor and particle phases at sufficient time resolution to define the importance of competing atmospheric processes. These measurements were supported by off-line analysis of the filters utilizing two-dimensional gas chromatography (GC x GC) with high-resolution time-of-flight mass spectrometry (HR-TOF-MS) using both electron impact (EI) and soft vacuum ultraviolet (VUV) ionization with derivatization. Speciated chemical data from SV-TAG and filter measurements were used to elucidate the relative importance of potential oxidation pathways by providing detailed information on the product distribution from atmospheric reactions and the quantification of known tracers for various oxidation pathways. Together, these techniques provided unequivocal molecular identification of a wide range of atmospheric organic compounds spanning the volatile, semi-volatile, and non-volatile phases. This level of chemical characterization provided insight into the chemical and physical processes that control the atmospheric oxidation of biogenic VOC and subsequent formation of SOA.