Aaron S. Katzenstein

Extensive regional atmospheric hydrocarbon pollution in the southwestern United States

Light alkane hydrocarbons are present in major quantities in the near-surface atmosphere of Texas, Oklahoma, and Kansas during both autumn and spring seasons. In spring 2002, maximum mixing ratios of ethane [34 parts per 109 by volume (ppbv)], propane (20 ppbv), and n-butane (13 ppbv) were observed in north-central Texas. The elevated alkane mixing ratios are attributed to emissions from the oil and natural gas industry. Measured alkyl nitrate mixing ratios were comparable to urban smog values, indicating active photochemistry in the presence of nitrogen oxides, and therefore with abundant formation of tropospheric ozone. We estimate that 4–6 teragrams of methane are released annually within the region and represents a significant fraction of the estimated total U.S. emissions. This result suggests that total U.S. natural gas emissions may have been underestimated. Annual ethane emissions from the study region are estimated to be 0.3–0.5 teragrams.

Large‐scale latitudinal and vertical distributions of NMHCs and selected halocarbons in the troposphere over the Pacific Ocean during the March‐April 1999 Pacific Exploratory Mission (PEM‐Tropics B)

Nonmethane hydrocarbons (NMHCs) and selected halocarbons were measured in whole air samples collected over the remote Pacific Ocean during NASAs Global Tropospheric Experiment (GTE) Pacific Exploratory Mission-Tropics B (PEM-Tropics B) in March and early April 1999. The large-scale spatial distributions of NMHCs and C2Cl4 reveal a much more pronounced north-south interhemispheric gradient, with higher concentrations in the north and lower levels in the south, than for the late August to early October 1996 PEM-Tropics A experiment. Strong continental outflow and winter-long accumulation of pollutants led to seasonally high Northern Hemisphere trace gas levels during PEM-Tropics B. Observations of enhanced levels of Halon 1211 (from developing Asian nations such as the PRC) and CH3Cl (from SE Asian biomass burning) support a significant southern Asian influence at altitudes above 1 km and north of 10°N. By contrast, at low altitude over the North Pacific the dominance of urban/industrial tracers, combined with low levels of Halon 1211 and CH3Cl, indicate a greater influence from developed nations such as Japan, Europe, and North America. Penetration of air exhibiting aged northern hemisphere characteristics was frequently observed at low altitudes over the equatorial central and western Pacific south to ∼5°S. The relative lack of southern hemisphere biomass burning sources and the westerly position of the South Pacific convergence zone contributed to significantly lower PEM-Tropics B mixing ratios of the NMHCs and CH3Cl south of 10°S compared to PEM-Tropics A. Therefore the trace gas composition of the South Pacific troposphere was considerably more representative of minimally polluted tropospheric conditions during PEM-Tropics B.

Air-quality implications of widespread adoption of cool roofs on ozone and particulate matter in southern California

Significance The South Coast Air Basin of California, a region of 16.8 million people, is among the most polluted air basins in the United States. A multidecadal effort to attain federal air-quality standards has led to significant progress, but much more work remains. Are recently implemented statewide building efficiency standards on rooftops counterproductive to these goals? With comprehensive regional models and intensive development of model input parameters, our research has identified the air-quality consequences that are expected to result from these efficiency standards. The results can inform policies to mitigate some air-quality penalties, while preserving the benefits of building efficiency standards. This work also sheds light on potential future policies aimed at reducing urban heating from pavement surfaces. The installation of roofing materials with increased solar reflectance (i.e., “cool roofs”) can mitigate the urban heat island effect and reduce energy use. In addition, meteorological changes, along with the possibility of enhanced UV reflection from these surfaces, can have complex impacts on ozone and PM2.5 concentrations. We aim to evaluate the air-quality impacts of widespread cool-roof installations prescribed by California’s Title 24 building energy efficiency standards within the heavily populated and polluted South Coast Air Basin (SoCAB). Development of a comprehensive rooftop area database and evaluation of spectral reflectance measurements of roofing materials allows us to project potential future changes in solar and UV reflectance for simulations using the Weather Research Forecast and Community Multiscale Air Quality (CMAQ) models. 2012 meteorological simulations indicate a decrease in daily maximum temperatures, daily maximum boundary layer heights, and ventilation coefficients throughout the SoCAB upon widespread installation of cool roofs. CMAQ simulations show significant increases in PM2.5 concentrations and policy-relevant design values. Changes in 8-h ozone concentrations depend on the potential change in UV reflectance, ranging from a decrease in population-weighted concentrations when UV reflectance remains unchanged to an increase when changes in UV reflectance are at an upper bound. However, 8-h policy-relevant ozone design values increase in all cases. Although the other benefits of cool roofs could outweigh small air-quality penalties, UV reflectance standards for cool roofing materials could mitigate these negative consequences. Results of this study motivate the careful consideration of future rooftop and pavement solar reflectance modification policies.