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Effects of Anthropogenic Pollutants on Biogenic Organic Aerosol Formation
Laboratory studies have long established that secondary organic aerosols (SOA) can be formed from biogenic and anthropogenic volatile organic compounds (VOC). However, the extent to which human activities alter SOA formation from biogenic emissions in the atmosphere is largely undetermined. We perform integrated laboratory chamber studies and field measurements to investigate the influences of anthropogenic emissions on biogenic SOA formation using advanced mass spectrometry techniques. A particular focus is on elucidating the effects of sulfate and NOx on isoprene and monoterpene SOA formation. Funding: NSF, EPA
H+(aq) (mol L-1 H2O) as a function of [H2Optcl] (μg m-3). All data points are grouped into nine subplots based on a 0.5 μg m-3 increment in [SO42-] and the size of data points represents [Isoprene-OA]. Figure from Xu et al., PNAS, 2015. Link to the article.
Aerosol Formation from Nitrate Radical Oxidation of Biogenic Volatile Organic Compounds
We perform laboratory chamber experiments to investigate SOA and organic nitrate formation and fates from nitrate radical (NO3) oxidation of biogenic hydrocarbons. We aim to obtain a deep understanding of the formation mechanisms and yields of organic nitrates, their properties, and their lifetimes with respect to further gas-phase oxidations and particle-phase reactions. Experiments are also conducted to study changes in gas and particle composition during the night-to-day transitions. Results from laboratory chamber studies provide fundamental data to evaluate the contribution of BVOC+NO3 to ambient aerosols, as well as parameters that can be used in models to predict organic nitrate formation and their impacts on NOx recycling and SOA formation. Funding: NSF, EPA
Aerosol mass yield as a function of organic mass loading for the β-pinene+NO3 reaction under “RO2+NO3 dominant” conditions. Figure from Boyd et al., ACP, 2015. Link to the article.
Linking Peroxy Radical and Gas-phase Chemistry to Aerosol Formation
Peroxy radicals formed from the oxidation of hydrocarbons play a critical role in the production of low-volatility compounds in SOA formation. We seek to perform explicit measurements of peroxy radicals and to experimentally map out the effects of different peroxy radical reaction channels on aerosol formation. We have developed a new technique for the direct measurement of hydroperoxy radicals using chemical ionization mass spectrometry. Our novel gas/aerosol instrumentations also allow for linking different peroxy radical reaction pathways to their corresponding molecular-level gas- and particle-phase composition. Funding: NSF, NASA
Schematic diagram of the High Resolution Time-of-Flight Chemical Ionization Mass Spectrometer (HR-ToF-CIMS). Figure from Sanchez et al., AMTD, 2016. Link to the article.
Aerosol Chemical Composition and Health Effects
Elevated concentrations of particulate matter (PM) have been associated with increases in the incidence of various cardiopulmonary diseases, which may be a result of PM-induced reactive oxygen and nitrogen species (ROS/RNS) production. In this project, the concentration of redox-active species in PM samples and intracellular ROS/RNS produced as a result of interactions between PM species and cells are measured using chemical and cellular assays, respectively. We have optimized a cellular assay for measuring ROS/RNS production in alveolar macrophage cells and cardiomyocytes upon exposure to PM samples. Combined with detailed characterization of PM chemical composition, we aim to better understand the oxidative properties of different types and components of PM mixtures. Funding: HEI
PM-induced reactive oxygen and nitrogen species (ROS/RNS) production in alveolar macrophage cells and cardiomyocytes. Link to the article.
Recent Field Studies
SOAS, Southern Oxidant and Aerosol Study; Centerville, AL, June-July 2013
We participated in six weeks of measurements at Centreville, AL as part of the SOAS field campaign in summer 2013. A High-Resolution Time-of-Flight Aerosol Mass spectrometer (HR-ToF-AMS) was deployed to investigate organic aerosol sources and the effects of anthropogenic emissions (SO2, NOx) on biogenic aerosol formation. Georgia Tech press release here. Funding: NSF, EPA
SCAPE, Southeastern Center for Air Pollution and Epidemiology; Atlanta, 2011-2016
SCAPE is an EPA funded-joint project between Georgia Tech and Emory University to study air quality and health effects of air pollution. We deployed a High- Resolution Time-of-Flight Aerosol Mass spectrometer (HR-ToF-AMS) and an Aerosol Chemical Speciation Monitor (ACSM) at multiple urban and rural SouthEastern Aerosol Research and Characterization (SEARCH) Network sites in multiple seasons in the greater Atlanta area, to characterize the chemical composition of submicron non-refractory particulate matter (NR-PM1) in the southeastern USA for links to their health impacts. Funding: EPA
ClearfLo, Clear Air for London; Detling, UK, January-February 2012
We deployed our High-Resolution Time-of-Flight Aerosol Mass spectrometer (HR-ToF-AMS) in Detling, UK, which is one of the sites of the ClearfLo project. ClearfLo is a large collaborative project involving multiple institutions in the UK and the US to investigate boundary layer pollution across London. Funding: DOE