Heterogeneous nitration reaction of BSA protein with urban air: improvements in experimental methodology.

Gas-phase ozone (O3) and nitrogen dioxide (NO2) can react with environmentally exposed proteins to induce chemical modifications such as the formation of nitrotyrosine (NTyr). Certain proteins with these modifications have also been shown to promote adverse health effects and can trigger an immune response. It is hypothesized that proteinaceous material suspended in the atmosphere as particulate matter, e.g., embedded in pollen, can undergo heterogenous reactions to produce chemically modified proteins that impact human health, especially in urban areas. To investigate the protein modification process under ambient outdoor reaction conditions, bovine serum albumin (BSA) protein samples were loaded onto filters and exposed to urban air in Denver, Colorado (USA). Losses and measurement artifacts were measured independently to calculate nitration effects on the protein via high-performance liquid chromatography and to support the experimental methodology. O3 loss from inlet lines using three commonly used particulate filters was quantified, showing a range of ambient O3 concentration losses from 3.2% for Kynar® (polyvinylidene fluoride) filters to > 60% for commonly used HEPA filters. Protein mass extraction efficiency was calculated as a function of filter material and protein mass using both native and nitrated BSA. Finally, we show examples of BSA samples nitrated by exposure to urban air as a proof-of-concept for future studies, highlighting the potential for atmospherically relevant NTyr formation. The methodology vetted here provides support for a wide variety of experimental efforts related to exposure of analytes to O3 and more broadly to an expanding field of protein modification in ambient air.

Ambient Mercury Observations near a Coal-Fired Power Plant in a Western U.S. Urban Area.

We report on the continuous ambient measurements of total gaseous mercury (TGM) and several ancillary air quality parameters that were collected in Colorado Springs, CO. This urban area, which is located adjacent to the Front Range of the Rocky Mountains, is the second largest metropolitan area in Colorado and has a centrally located coal-fired power plant that installed mercury (Hg) emission controls the year prior to our study. There are few other Hg point sources within the city. Our results, which were obtained from a measurement site < 1 km from the power plant, show a distinct diel pattern in TGM, with peak concentrations occurring during the night (1.7 ± 0.3 ng m-3) and minimum concentrations mid-day (1.5 ± 0.2 ng m-3). The TGM concentrations were not correlated with wind originating from the direction of the plant or with sulfur dioxide (SO2) mixing ratios, and they were not elevated when the atmospheric mixing height was above the effective stack height. These findings suggest that the current Hg emissions from the CFPP did not significantly influence local TGM, and they are consistent with the facility's relatively low reported annual emissions of 0.20 kg Hg per year. Instead, variability in the regional signal, diurnal meteorological conditions, and/or near-surface emission sources appears to more greatly influence TGM at this urban site.

Long-term evaluation of air sensor technology under ambient conditions in Denver, Colorado.

Air pollution sensors are quickly proliferating for use in a wide variety of applications, with a low price point that supports use in high-density networks, citizen science, and individual consumer use. This emerging technology motivates the assessment under real-world conditions, including varying pollution levels and environmental conditions. A seven-month, systematic field evaluation of low-cost air pollution sensors was performed in Denver, Colorado, over 2015-2016; the location was chosen to evaluate the sensors in a high-altitude, cool, and dry climate. A suite of particulate matter (PM), ozone (O3), and nitrogen dioxide (NO2) sensors were deployed in triplicate and were collocated with federal equivalent method (FEM) monitors at an urban regulatory site. Sensors were evaluated for their data completeness, correlation with reference monitors, and ability to reproduce trends in pollution data, such as daily concentration values and wind-direction patterns. Most sensors showed high data completeness when data loggers were functioning properly. The sensors displayed a range of correlations with reference instruments, from poor to very high (e.g., hourly-average PM Pearson correlations with reference measurements varied from 0.01 to 0.86). Some sensors showed a change in response to laboratory audits/testing from before the sampling campaign to afterwards, such as Aeroqual, where the O3 response slope changed from about 1.2 to 0.6. Some PM sensors measured wind-direction and time-of-day trends similar to those measured by reference monitors, while others did not. This study showed different results for sensor performance than previous studies performed by the U.S. EPA and others, which could be due to different geographic location, meteorology, and aerosol properties. These results imply that continued field testing is necessary to understand emerging air sensing technology.