Polycyclic aromatic compounds (PACs) are known due to their mutagenic activity. Among them, 2-nitrobenzanthrone (2-NBA) and 3-nitrobenzanthrone (3-NBA) are considered as two of the most potent mutagens found in atmospheric particles. In the present study 2-NBA, 3-NBA and selected PAHs and Nitro-PAHs were determined in fine particle samples (PM 2.5) collected in a bus station and an outdoor site. The fuel used by buses was a diesel-biodiesel (96:4) blend and light-duty vehicles run with any ethanol-to-gasoline proportion. The concentrations of 2-NBA and 3-NBA were, on average, under 14.8 µg g−1 and 4.39 µg g−1, respectively. In order to access the main sources and formation routes of these compounds, we performed ternary correlations and multivariate statistical analyses. The main sources for the studied compounds in the bus station were diesel/biodiesel exhaust followed by floor resuspension. In the coastal site, vehicular emission, photochemical formation and wood combustion were the main sources for 2-NBA and 3-NBA as well as the other PACs. Incremental lifetime cancer risk (ILCR) were calculated for both places, which presented low values, showing low cancer risk incidence although the ILCR values for the bus station were around 2.5 times higher than the ILCR from the coastal site.

Occurrence of the potent mutagens 2- nitrobenzanthrone and 3-nitrobenzanthrone in fine airborne particles

Numerical assessments of global air quality and potential changes in atmospheric chemical constituents require estimates of the surface fluxes of a variety of trace gas species. We have developed a global model to estimate emissions of volatile organic compounds from natural sources (NVOC). Methane is not considered here and has been reviewed in detail elsewhere. The model has a highly resolved spatial grid (0.5° × 0.5° latitude/longitude) and generates hourly average emission estimates. Chemical species are grouped into four categories: isoprene, monoterpenes, other reactive VOC (ORVOC), and other VOC (OVOC). NVOC emissions from oceans are estimated as a function of geophysical variables from a general circulation model and ocean color satellite data. Emissions from plant foliage are estimated from ecosystem specific biomass and emission factors and algorithms describing light and temperature dependence of NVOC emissions. Foliar density estimates are based on climatic variables and satellite data. Temporal variations in the model are driven by monthly estimates of biomass and temperature and hourly light estimates. The annual global VOC flux is estimated to be 1150 Tg C, composed of 44% isoprene, 11% monoterpenes, 22.5% other reactive VOC, and 22.5% other VOC. Large uncertainties exist for each of these estimates and particularly for compounds other than isoprene and monoterpenes. Tropical woodlands (rain forest, seasonal, drought-deciduous, and savanna) contribute about half of all global natural VOC emissions. Croplands, shrublands and other woodlands contribute 10–20% apiece. Isoprene emissions calculated for temperate regions are as much as a factor of 5 higher than previous estimates.

/pdf/a-global-model-of-natural-volatile-organic-compound-546vyk3ww5.pdf

A global model of natural volatile organic compound emissions

. Reactive gases and aerosols are produced by terrestrial ecosystems, processed within plant canopies, and can then be emitted into the above-canopy atmosphere. Estimates of the above-canopy fluxes are needed for quantitative earth system studies and assessments of past, present and future air quality and climate. The Model of Emissions of Gases and Aerosols from Nature (MEGAN) is described and used to quantify net terrestrial biosphere emission of isoprene into the atmosphere. MEGAN is designed for both global and regional emission modeling and has global coverage with ~1 km2 spatial resolution. Field and laboratory investigations of the processes controlling isoprene emission are described and data available for model development and evaluation are summarized. The factors controlling isoprene emissions include biological, physical and chemical driving variables. MEGAN driving variables are derived from models and satellite and ground observations. Tropical broadleaf trees contribute almost half of the estimated global annual isoprene emission due to their relatively high emission factors and because they are often exposed to conditions that are conducive for isoprene emission. The remaining flux is primarily from shrubs which have a widespread distribution. The annual global isoprene emission estimated with MEGAN ranges from about 500 to 750 Tg isoprene (440 to 660 Tg carbon) depending on the driving variables which include temperature, solar radiation, Leaf Area Index, and plant functional type. The global annual isoprene emission estimated using the standard driving variables is ~600 Tg isoprene. Differences in driving variables result in emission estimates that differ by more than a factor of three for specific times and locations. It is difficult to evaluate isoprene emission estimates using the concentration distributions simulated using chemistry and transport models, due to the substantial uncertainties in other model components, but at least some global models produce reasonable results when using isoprene emission distributions similar to MEGAN estimates. In addition, comparison with isoprene emissions estimated from satellite formaldehyde observations indicates reasonable agreement. The sensitivity of isoprene emissions to earth system changes (e.g., climate and land-use) demonstrates the potential for large future changes in emissions. Using temperature distributions simulated by global climate models for year 2100, MEGAN estimates that isoprene emissions increase by more than a factor of two. This is considerably greater than previous estimates and additional observations are needed to evaluate and improve the methods used to predict future isoprene emissions.

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Estimates of global terrestrial isoprene emissions using MEGAN (Model of Emissions of Gases and Aerosols from Nature)

In this review, we highlight the use of organic photoredox catalysts in a myriad of synthetic transformations with a range of applications. This overview is arranged by catalyst class where the photophysics and electrochemical characteristics of each is discussed to underscore the differences and advantages to each type of single electron redox agent. We highlight both net reductive and oxidative as well as redox neutral transformations that can be accomplished using purely organic photoredox-active catalysts. An overview of the basic photophysics and electron transfer theory is presented in order to provide a comprehensive guide for employing this class of catalysts in photoredox manifolds.

Organic Photoredox Catalysis

Rapid industrialization and urbanization in developing countries has led to an increase in air pollution, along a similar trajectory to that previously experienced by the developed nations. In China, particulate pollution is a serious environmental problem that is influencing air quality, regional and global climates, and human health. In response to the extremely severe and persistent haze pollution experienced by about 800 million people during the first quarter of 2013 (refs 4, 5), the Chinese State Council announced its aim to reduce concentrations of PM2.5 (particulate matter with an aerodynamic diameter less than 2.5 micrometres) by up to 25 per cent relative to 2012 levels by 2017 (ref. 6). Such efforts however require elucidation of the factors governing the abundance and composition of PM2.5, which remain poorly constrained in China. Here we combine a comprehensive set of novel and state-of-the-art offline analytical approaches and statistical techniques to investigate the chemical nature and sources of particulate matter at urban locations in Beijing, Shanghai, Guangzhou and Xi'an during January 2013. We find that the severe haze pollution event was driven to a large extent by secondary aerosol formation, which contributed 30-77 per cent and 44-71 per cent (average for all four cities) of PM2.5 and of organic aerosol, respectively. On average, the contribution of secondary organic aerosol (SOA) and secondary inorganic aerosol (SIA) are found to be of similar importance (SOA/SIA ratios range from 0.6 to 1.4). Our results suggest that, in addition to mitigating primary particulate emissions, reducing the emissions of secondary aerosol precursors from, for example, fossil fuel combustion and biomass burning is likely to be important for controlling China's PM2.5 levels and for reducing the environmental, economic and health impacts resulting from particulate pollution.

/pdf/high-secondary-aerosol-contribution-to-particulate-pollution-2bz0fbxzvu.pdf

High secondary aerosol contribution to particulate pollution during haze events in China

Kinetics of the reactions of ozone and hydroxyl radicals with furan and thiophene at 298 .+-. 2 k

: This report documents the results of the first phase of a two-phase program aimed at developing for the U.S. Air Force experimentally tested computer models to predict worst-case potentials for air quality degradation resulting from use of current and potential future turbine engine (jet) fuels. The development and testing of such models requires an adequate data base derived from appropriate environmental chamber experiments and laboratory studies. In Phase I of this two-phase program, a total of 131 environmental chamber experiments were carried out in a approx. 640000-liter, all Teflon indoor environmental chamber and several kinetic measurements were made in order to obtain data required for model development. The chamber experiments included 47 single component-NOx-air irradiations of various representative fuel constituents and potential future fuel impurities, 15 fuel-NOx-air irradiations of various representative fuel constituents and potential future fuel impurities, 15 fuel--NOx-air irradiations employing one whole and six synthetic surrogate fuels, and 69 control or characterizatin runs. Volume II contains a tabulation of the environmental chamber data gathered during the course of the experimental phase of this program.

Atmospheric photochemical modeling of turbine engine fuels. Phase 1: Experimental studies. Volume 2: Environmental chamber data tabulations

Rate constants for the reaction of hydroxyl radicals with ethylene over the temperature range 229-425°k

Relative rate constants for the reaction of oxygen(3P) atoms with selected olefins, monoterpenes, and unsaturated aldehydes

Rate constants for the reaction of OH radicals with CHF2Cl, CF2Cl2, CFCl3, and H2 have been determined over the temperature range 297–434 °K using a flash photolysis–resonance fluorescence technique. The following Arrhenius expressions were obtained: k1(CHF2Cl) =1.21×10−12e−(3250±300)/RT cm3 molecule−1 sec−1, k1(CF2Cl2) <1×10−15 cm3 molecule−1 sec−1 (T=297–424 °K), k1(CFCl3) <1×10−15 cm3 molecule−1 sec−1 (T=297–424 °K), k1(H2) =5.9×10−12 e−(3990±300)/RT cm3 molecule−1 sec−1. The rate constants for the reaction of OH radicals with H2, which were used to check the experimental system, are in good agreement with literature values. The atmospheric significance of the reaction of OH radicals with CHF2Cl is briefly discussed.

Roger Atkinson

Papers

Kinetics of the reactions of ozone and hydroxyl radicals with furan and thiophene at 298 .+-. 2 k

Atmospheric photochemical modeling of turbine engine fuels. Phase 1: Experimental studies. Volume 2: Environmental chamber data tabulations

Rate constants for the reaction of hydroxyl radicals with ethylene over the temperature range 229-425°k

Relative rate constants for the reaction of oxygen(3P) atoms with selected olefins, monoterpenes, and unsaturated aldehydes

Rate constants for the reaction of oh radicals with chf2cl, cf2cl2, cfcl3, and h2 over the temperature range 297-434 k