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.

/pdf/estimates-of-global-terrestrial-isoprene-emissions-using-2inhk36wkp.pdf

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

Using a relative rate method with in situ generation of the hydroxyaldehydes, rate constants for the reactions of the OH radical with 2-hydroxybutanal [CH3CH2CH(OH)CHO], 3-hydroxybutanal [CH3CH(OH)CH2CHO], 2-hydroxypropanal [CH3CH(OH)CHO], 2-hydroxy-2-methylpropanal [(CH3)2C(OH)CHO], and 3-hydroxypropanal [HOCH2CH2CHO] have been measured at atmospheric pressure and 296 ± 2 K. The hydroxyaldehydes were generated in situ from the OH radical-initiated reactions of precursor compounds (1,2- and 1,3-butanediol, 2-methyl-2,4-pentanediol, 2-methyl-3-buten-2-ol, and cis-3-hexen-1-ol) and the rate constants for the reaction of OH radicals with the hydroxyaldehydes were determined relative to those for reaction of OH radicals with the precursor compound. The rate constants obtained (in units of 10-11 cm3 molecule-1 s-1) were CH3CH2CH(OH)CHO, 2.37 ± 0.23; CH3CH(OH)CH2CHO, 2.95 ± 0.24; CH3CH(OH)CHO, 1.70 ± 0.20; (CH3)2C(OH)CHO, 1.40 ± 0.25; and HOCH2CH2CHO, 1.99 ± 0.29.

Rate Constants for the Gas-Phase Reactions of OH Radicals with a Series of Hydroxyaldehydes at 296 ± 2 K

Relative rate constants have been measured at 300 K and 1 atm total pressure for reactions of HO/sub 2/ with HO/sub 2/, SO/sub 2/, CO, N/sub 2/O, trans-2-butene, and 2,3-dimethyl-2-butene. The thermal decomposition of HO/sub 2/NO/sub 2/ was used as a source of HO/sub 2/ radicals, and rate constants were measured relative to that of HO/sub 2/ + NO/sub 2/ reaction. A rate constant of 3.8 x 10-12 cm3/molecule/s (total uncertainty is a factor of 2) was measured for the HO/sub 2/ disproportionation reaction; the good agreement of this value with the average literature value of approx 3 x 10-12 cm3/molecule/s supports the validity of the present experimental techniques. Rate constate upper limits of 1 x 10/sup -18/, 2 x 10/sup -20/, and 4 x 10/sup -18/ cm3/molecule/S were obtained for the reactions of HO/sub 2/ with SO/sub 2/, N/sub 2/O, and trans-2-butene, respectively; these values indicate that the reactions will be of negligible atmospheric importance. Significant reaction rates were observed with CO and 2,3-dimethyl-2-butene and may correspond to HO/sub 2/ rate constants as large as 2 x 10-19 and 4 x 10-17 cm3/molecule/S, respectively; these values must be regarded as only upper limits because of the possible effects ofmore » large amounts of the reactants on HO/sub 2/NO/sub 2/ in the gas phase or on the cell surfaces.« less

Rate constants for the reaction of hydroperoxyl radicals with hydroperoxyl radicals, sulfur dioxide, carbon monoxide, nitrous oxide, trans-2-butene, and 2,3-dimethyl-2-butene at 300 K

Relative rate constants for the reaction of OH radicals with a series of branched alkanes have been determined at 297 ± 2 K, using methyl nitrite photolysis in air as a source of OH radicals. Using a rate constant for the reaction of OH radicals with n-butane of 2.58 × 10−12 cm3/molecule · s, the rate constants obtained are (× 1012 cm3/molecule · s): isobutane, 2.29 ± 0.06; 2-methylbutane, 3.97 ± 0.11; 2,2-dimethylbutane, 2.66 ± 0.08; 2-methylpentane, 5.68 ± 0.24; 3-methylpentane, 5.78 ± 0.11; 2,2,3-trimethylbutane, 4.21 ± 0.08; 2,4-dimethylpentane, 5.26 ± 0.11; methylcyclohexane, 10.6 ± 0.3; 2,2,3,3-tetramethylbutane, 1.06 ± 0.08; and 2,2,4-trimethylpentane, 3.66 ± 0.16. Rate constants for 2,2-dimethylbutane, 2,4-dimethylpentane, and methylclohexane have been determined for the first time, while those for the other branched alkanes are in generally good agreement with the literature data. Primary, secondary, and tertiary group rate constants at room temperature have been derived from these and previous data for alkanes and unstrained cycloalkanes, with the secondary and tertiary group rate constants depending in a systematic manner on the identity of the neighboring groups. The use of these group rate constants, together with a previous determination of the effect of ring strain energy on the OH radical rate constants for a series of cycloalkanes, allows the a priori estimation of OH radical rate constants for alkanes and cycloalkanes at room temperature.

Kinetics of the reaction of oh radicals with a series of branched alkanes at 297 ± 2 K

Rate constants for the reaction of OH radicals with n-propyl acetate, sec-butyl acetate, tetrahydrofuran and peroxyacetyl nitrate

Relative rate constants for the gas-phase reactions of OH radicals with a series of alkyl nitrates have been determined at 299 ± 2 K, using methyl nitrite photolysis in air as a source of OH radicals. Using a rate constant for the reaction of OH radicals with cyclohexane of 7.57 × 10−12 cm3/molec·s, the rate constants obtained are (× 1012 cm3/molec·s): 2-propyl nitrate, 0.18 ± 0.05; 1-butyl nitrate, 1.42 ± 0.11; 2-butyl nitrate, 0.69 ± 0.10; 2-pentyl nitrate, 1.87 ± 0.12; 3-pentyl nitrate, 1.13 ± 0.20; 2-hexyl nitrate, 3.19 ± 0.16; 3-hexyl nitrate, 2.72 ± 0.22; 3-heptyl nitrate, 3.72 ± 0.43; and 3-octyl nitrate, 3.91 ± 0.80. These rate constants, which are the first reported for the alkyl nitrates, are significantly lower than those for the parent alkanes, and a formula, based on the numbers of the various types of CH bonds in the alkyl nitrates, is derived for rate constant estimation purposes.

Roger Atkinson

Papers

Rate Constants for the Gas-Phase Reactions of OH Radicals with a Series of Hydroxyaldehydes at 296 ± 2 K

Rate constants for the reaction of hydroperoxyl radicals with hydroperoxyl radicals, sulfur dioxide, carbon monoxide, nitrous oxide, trans-2-butene, and 2,3-dimethyl-2-butene at 300 K

Kinetics of the reaction of oh radicals with a series of branched alkanes at 297 ± 2 K

Rate constants for the reaction of OH radicals with n-propyl acetate, sec-butyl acetate, tetrahydrofuran and peroxyacetyl nitrate

Kinetics of the gas‐phase reactions of OH radicals with alkyl nitrates at 299 ± 2 K