My group’s main interests are the sources and chemical transformations of air pollutants in the atmosphere and indoor environments, the formation of ozone and secondary organic aerosol, and the impact that these processes have on air quality, climate change, and human health. To study these issues, we use measurements of organic compounds by mass spectrometry and gas chromatography. We also analyze the results from satellite remote sensing measurements of air pollutants and greenhouse gases.
Urban Air Quality
We study the processes that determine urban air quality in cities. Volatile organic compounds (VOCs) are important precursors of ozone and organic aerosol formation. Their emissions in cities used to be dominated by use of transportation fuels, but these have been reduced significantly and nowadays other sources have become relatively much more important including those from the use of household chemicals, cleaners, personal care products, paints, inks, glues and many other products. We study VOC emissions in cities and their chemical transformations using mass spectrometry and gas chromatography. We are also studying how these emissions changed temporarily during the Covid-19 lockdowns in 2020.
The largest source of VOCs worldwide is from vegetation. The oxidation of biogenic hydrocarbons like isoprene and monoterpenes plays a key role in the oxidant budget of the atmosphere and the formation of organic aerosols. We are currently studying the oxidation of monoterpenes in the laboratory. The gas-phase products are detected by mass spectrometry, and identified by the presumed reaction mechanisms, ion fragmentation pathways and the physical separation by wall losses in the instrumentation.
The chemical composition of indoor air has received far less attention than pollution in the ambient atmosphere. We have made measurements inside different buildings on the campus of CU Boulder, including a classroom, art museum, and athletic center. We have found that ambient air, the outgassing of materials and people themselves are important sources of VOCs indoors. In the athletic center, we observed the products of chemical reactions that result from the use of chlorine-containing cleaners. The extent to which these VOCs can be mixed out of buildings depends on their vapor pressure and solubility.
Emissions from Oil and Natural Gas Production
Since the mid 2000s, the U.S. has seen a strong increase in the production of natural gas and crude oil from shale formations thanks to the development of horizontal drilling and hydraulic fracturing. Associated with this industrial activity are emissions of the greenhouse gas methane, ozone precursors such as nitrogen oxides and VOCs, and air toxics such as benzene and hydrogen sulfide. Ozone formation from these emissions has been observed in the winter in basins in Utah and Wyoming. We are studying the magnitude of NOx and methane emissions and their spatial distributions and temporal trends using data from the satellite-based Ozone Monitoring Instrument (OMI) and Tropospheric Monitoring Instrument (TropOMI).