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Nighttime concentrations of the gas phase nitrate radical (NO 3 ) were successfully measured during a four week field campaign in an arid urban location, Reno Nevada, using long-path Differential Optical Absorbance Spectrometry (DOAS). While typical concentrations of NO 3 ranged from 5 to 20 ppt, elevated concentrations were observed during a wildfire event. Horizontal mixing in the free troposphere was considerable because the sampling site was above the stable nocturnal boundary layer every night and this justified a box modeling approach. Process analysis of box model simulations showed NO 3 accounted for approximately half of the loss of internal olefins, 60% of the isoprene loss, and 85% of the α-pinene loss during the nighttime hours during a typical night of the field study. The NO 3 + aldehyde reactions were not as important as anticipated. On a polluted night impacted by wildfires upwind of the sampling location, NO 3 reactions were more important. Model simulations overpredicted NO 2 concentrations for both case studies and inorganic chemistry was the biggest influence on NO 3 concentrations and on nitric acid formation. The overprediction may be due to additional NO 2 loss processes that were not included in the box model, as deposition and N 2 O 5 uptake had no significant effect on NO 2 levels. [ABSTRACT FROM AUTHOR]

The Arabian Peninsula experiences severe air pollution, the extent and sources of which are poorly documented. Each year in Saudi Arabia this situation is intensified during Hajj, the Holy Pilgrimage of Islam that draws millions of pilgrims to Mecca. An initial study of air quality in Mecca and surrounding holy sites during the 2012 Hajj (October 24-27) revealed strongly elevated levels of the combustion tracer carbon monoxide (CO, up to 57 ppmv) and volatile organic compounds (VOCs) along the pilgrimage route-especially in the tunnels of Mecca-that are a concern for human health. The most abundant VOC was the gasoline evaporation tracer i-pentane, which exceeded 1200 ppbv in the tunnels. Even though VOC concentrations were generally lower during a follow-up non-Hajj sampling period (April 2013), many were still comparable to other large cities suffering from poor air quality. Major VOC sources during the 2012 Hajj study included vehicular exhaust, gasoline evaporation, liquefied petroleum gas, and air conditioners. Of the measured compounds, reactive alkenes and CO showed the strongest potential to form ground-level ozone. Because the number of pilgrims is expected to increase in the future, we present emission reduction strategies to target both combustive and evaporative fossil fuel sources. [ABSTRACT FROM AUTHOR]

Abstract: The “Industrial Heartland” of Alberta is Canada's largest hydrocarbon processing center, with more than 40 major chemical, petrochemical, and oil and gas facilities. Emissions from these industries affect local air quality and human health. This paper characterizes ambient levels of 77 volatile organic compounds (VOCs) in the region using high-precision measurements collected in summer 2010. Remarkably strong enhancements of 43 VOCs were detected, and concentrations in the industrial plumes were often similar to or even higher than levels measured in some of the world's largest cities and industrial regions. For example maximum levels of propene and i-pentane exceeded 100 ppbv, and 1,3-butadiene, a known carcinogen, reached 27 ppbv. Major VOC sources included propene fractionation, diluent separation and bitumen processing. Emissions of the measured VOCs increased the hydroxyl radical reactivity (k OH), a measure of the potential to form downwind ozone, from 3.4 s−1 in background air to 62 s−1 in the most concentrated plumes. The plume value was comparable to polluted megacity values, and acetaldehyde, propene and 1,3-butadiene contributed over half of the plume k OH. Based on a 13-year record (1994–2006) at the county level, the incidence of male hematopoietic cancers (leukemia and non-Hodgkin lymphoma) was higher in communities closest to the Industrial Heartland compared to neighboring counties. While a causal association between these cancers and exposure to industrial emissions cannot be confirmed, this pattern and the elevated VOC levels warrant actions to reduce emissions of known carcinogens, including benzene and 1,3-butadiene. [ABSTRACT FROM AUTHOR]

A sampling campaign was conducted in the city of Milan, Italy before and during a transportation strike in January 2004. This strike provided a unique opportunity to investigate the influence of public transportation on the air quality in a major metropolitan area. Twenty-four air samples were collected each day around the city on January 2nd, 7th and 9th. The samples were analyzed for methane, carbon monoxide, non-methane hydrocarbons (NMHCs), halocarbons and alkyl nitrates. Significant differences in the mixing ratios were observed among the three days of sampling, with January 2nd showing the lowest concentrations as a result of decreased activity in the city during the holiday season. January 9th showed the highest NMHC concentrations because of increased vehicular activity in the city due to a public transportation strike. This paper investigates the correlation between the increased number of vehicles and decreased air quality because of a reduction in public transportation. Computer simulations were able to reproduce measurements of ozone production during the January 2004 strike and a July 2005 strike. The measurements and simulations suggest that reduced VOC emissions due to the existence of public transportation lowers peak ozone by 11–33% during the summer months. [Copyright &y& Elsevier]