Analytical Chemistry for the Atmosphere

Just published!

An omnipresent diversity and variability in the chemical composition of atmospheric functionalized organic aerosol” in Nature’s Communications Chemistry.

There is also a companion highlight article available here and a press release from Yale here.

Several of the research objectives of our group are achieved through a mix of instrument development to measure previously understudied compounds; field/lab measurements; and detailed analyses using novel statistical methods to elucidate sources, emissions, and impacts on air quality.

Check out our work on novel air quality monitors for high spatiotemporal analyses!

Part of our work focuses on the development of custom measurement instrumentation (ex. gas chromatography and mass spectrometry) to measure unexplored chemistry and compounds in the atmosphere.  Analysis of the resulting data using statistical method and modeling techniques reveals important discoveries about the emissions and chemical/physical processes in the atmosphere with implications for climate and human health.

Welcome to the equivalent of deep sea/deep space exploration in the atmosphere!

Multi-dimensional chromatography/spectrometry separates complex mixtures in the atmosphere (ex. shown by volatility/size (x-axis) and polarity (y-axis))

Organic compounds are ubiquitous throughout the atmosphere and include over 10,000 individual chemical species that exist in the gas phase, particle phase, or distributed between the two phases. Many gas-phase organic compounds are important precursors to the formation of secondary organic aerosol (SOA) and tropospheric ozone. Some compounds are also of concern as primary pollutants due to their acute and chronic health effects, influence on climate change, and/or ability to deplete stratospheric ozone. Both tropospheric ozone and SOA have detrimental effects on human health and implications for climate change. Many aspects regarding the emissions of gas-phase organic carbon and the formation mechanisms leading to SOA and ozone are poorly understood and regulatory agencies lack sufficient information to develop effective control strategies for regions affected by detrimental air quality.

Chromatogram for an atmospheric sample highlighting 3 compound classes of interest (alkanes, aromatics, and PAHs). Each peak represents a compound in the atmosphere with its concentration proportional to peak size. Each is measured as it elutes from a 30 meter capillary column that separates compounds based on volatility.

Comparison of the chromatographic separation of gasoline and diesel fuel across several compound classes of interest including compound in the less-studied Intermediate Volatility Organic Compound (IVOC) range (Gentner et al., PNAS 2012)

Organic carbon in the gas-phase can be classified by vapor pressure and is generally divided into Volatile Organic Compound (VOC), Intermediate Volatility Organic Compound (IVOC), and Semi-Volatile Organic Compound (SVOC) classes, or ranges. Gas-phase organic carbon exists over a wide range of molecular sizes (containing 1-25 carbon atoms) and functionalities, which together determine their volatility (i.e. their partitioning between the gas and particle phase). A large fraction of organic compounds have rarely, or never, been measured in the atmosphere, especially those in the IVOC range, as historically gas-phase measurements have typically been limited to compounds with volatilities higher than alkanes with 8-10 carbon atoms. This can be attributed to the difficulty of measuring these compounds compared to much smaller compounds with greater abundances in the atmosphere. Additionally, it is much easier to sample and analyze light VOCs or much lower vapor pressure compounds that are entirely in the particle phase. Organic compounds can also be classified by chemical type and include, but are not limited to, alkanes, alkenes, alkynes, aromatics, polycyclic aromatic hydrocarbons (PAHs), and those with functional groups containing one or more oxygen, nitrogen, or halogen species. Sources are both biogenic and anthropogenic with varying degrees of characterization and uncertainty depending on historical importance and extent of research on individual source categories.

Analysis methods include statistical methods of source apportionment, emission rates, chemistry, secondary pollutant yields, dispersion, and much more! Examples can be found in many of our papers:

Statistical regression of analyzed compounds allows for assessment of prominent sources (Gentner et al., ACP 2014)