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)

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

Secondary organic aerosol (SOA) accounts for a significant fraction of ambient tropospheric aerosol and a detailed knowledge of the formation, properties and transformation of SOA is therefore required to evaluate its impact on atmospheric processes, climate and human health. The chemical and physical processes associated with SOA formation are complex and varied, and, despite considerable progress in recent years, a quantitative and predictive understanding of SOA formation does not exist and therefore represents a major research challenge in atmospheric science. This review begins with an update on the current state of knowledge on the global SOA budget and is followed by an overview of the atmospheric degradation mechanisms for SOA precursors, gas-particle partitioning theory and the analytical techniques used to determine the chemical composition of SOA. A survey of recent laboratory, field and modeling studies is also presented. The following topical and emerging issues are highlighted and discussed in detail: molecular characterization of biogenic SOA constituents, condensed phase reactions and oligomerization, the interaction of atmospheric organic components with sulfuric acid, the chemical and photochemical processing of organics in the atmospheric aqueous phase, aerosol formation from real plant emissions, interaction of atmospheric organic components with water, thermodynamics and mixtures in atmospheric models. Finally, the major challenges ahead in laboratory, field and modeling studies of SOA are discussed and recommendations for future research directions are proposed.

/pdf/the-formation-properties-and-impact-of-secondary-organic-4x4th6v9ke.pdf

The formation, properties and impact of secondary organic aerosol: current and emerging issues

Rate constants for the gas-phase reactions of OH radicals with the C6−C14 2-methyl-1-alkenes and the C6−C10 trans-2-alkenes have been measured at 299 ± 2 K and atmospheric pressure of air using a relative rate technique. The rate constants obtained (in units of 10−11 cm3 molecule−1 s−1) were as follows: 2-methyl-1-pentene, 5.67 ± 0.21; 2-methyl-1-hexene, 6.50 ± 0.11; 2-methyl-1-heptene, 6.71 ± 0.21; 2-methyl-1-octene, 7.02 ± 0.16; 2-methyl-1-nonene, 7.28 ± 0.21; 2-methyl-1-decene, 7.85 ± 0.26; 2-methyl-1-undecene, 7.85 ± 0.21; 2-methyl-1-dodecene, 7.96 ± 0.26; 2-methyl-1-tridecene, 8.06 ± 0.37; trans-2-hexene, 6.08 ± 0.26; trans-2-heptene, 6.76 ± 0.32; trans-2-octene, 7.23 ± 0.21; trans-2-nonene, 7.54 ± 0.16; and trans-2-decene, 7.80 ± 0.26, where the indicated errors are two least-squares standard deviations and do not include the uncertainty associated with the rate constant for the reference compound α-pinene. Our data show that the rate constants for the reactions of OH radicals with 2-methyl-1-alkene...

Rate constants for the gas-phase reactions of OH radicals with a series of C6-C14 alkenes at 299 +/- 2 K.

The kinetics and nitroarene product yields of the gas-phase reactions of naphthalene-d 8 , fluoranthene-d 10 , and pyrene with OH radicals in the presence of NO x and in N 2 O 5 -No 3 -NO 2 -air mixtures have been investigated at 296±2 K and atmospheric pressure of air. Using a relative rate method, naphthalene-d 8 was shown to react in N 2 O 5 −NO 2 3−NO 2 −air mixtures a factor of 1.22±0.10 times faster than than did naphthalene, with the 1- and 2-nitronaphthalene-d 7 product yields being similar to those of 1- and 2-nitronaphthalene from naphthalene. From the measured PAH concentrations and the nitroarene product yields, formation yields of 2-, 7-, and 8-nitrofluoranthene-d 9 and 2- and 4-nitropyrene of 0.03, 0.01, 0.003, 0.005, and 0.0006, respectively, were determined from the OH radical-initiated reactions. Effective rate constants for the reactions of fluoranthene-d 10 and pyrene with N 2 O 5 in N 2 O 5 −NO 3 −NO 2 −air mixtures of ca. 1.8×10 −17 cm 3 molecule −1 s −1 and ca. 5.6×10 −17 cm 3 molecule −1 s -1 , respectively, were derived. Formation yields of 2-nitrofluororanthene-d 9 and 4-nitropyrene of ca. 0.24 and ca. 0.0006, respectively, were estimated for these reaction systems. 2-nitropyrene was also observed to be formed in these N 2 O 5 −NO 3 −NO 2 reactions, but was found to be a function of the NO 2 concentration and, therefore, would be a negligible product under ambient NO 2 concentrations. These product and kinetic data are consistent with ambient air measurements of the nitroarene concentrations

Kinetics and Nitro‐Products of the Gas‐Phase OH and NO3 Radical‐Initiated Reactions of Naphthalene‐d8, Fluoranthene‐d10, and Pyrene.

Kinetics of the gas‐phase reactions of NO3 radicals and O3 with 3‐methylfuran and the OH radical yield from the O3 reaction

Biogenic volatile organic compounds (BVOC) were measured at Azusa and at either Pine Mountain or Mount Baldy, elevated sites 11 km north and 25 km northeast of Azusa, respectively, during four intensive sampling periods of the 1997 Southern California Ozone Study. During the sampling periods there was a consistent pattern of isolation of the mountain sites from valley air masses at night, followed by transport of valley air with elevated levels of O3 and NOx to the mountain sites as the mixing height increased throughout the day. Isoprene was the dominant BVOC at the mountain sites with afternoon concentrations reaching 2 ppbv, and its decrease to a low mixing ratio after sunset was attributed to reaction with NO3 radicals. At Azusa the BVOC mixing ratios were highest in the morning with the concentrations of monoterpenes and of methacrolein (MACR) and methyl vinyl ketone (MVK), isoprene photooxidation products, generally exceeding the maximum isoprene measured at Azusa. The high daytime ratio of (MVK + MACR)/isoprene suggested that nighttime drainage flows into Azusa, from elevated sites where the isoprene was depleted by chemical reaction, may have been responsible for much of the isoprene and its photoxidation products. The data also indicated local isoprene sources at Azusa and a possible contribution of MVK and MACR from vehicle emissions. Instances of high mixing ratios of limonene at Azusa suggested an intermittent anthropogenic source. During this study, particularly in early morning, BVOC are calculated to make a significant contribution to peroxy radical formation at Azusa.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2000JD900517

Biogenic volatile organic compounds at Azusa and elevated sites during the 1997 Southern California Ozone Study

Using relative rate methods, rate constants for the gas-phase reactions of OH radicals and Cl atoms with di-n-propyl ether, di-n-propyl ether-d14, di-n-butyl ether and di-n-butyl ether-d18 have been measured at 296 ± 2 K and atmospheric pressure of air. The rate constants obtained (in cm3 molecule−1 s−1 units) were: OH radical reactions, di-n-propyl ether, (2.18 ± 0.17) × 10−11; di-n-propyl ether-d14, (1.13 ± 0.06) × 10−11; di-n-butyl ether, (3.30 ± 0.25) × 10−11; and di-n-butyl ether-d18, (1.49 ± 0.12) × 10−11; Cl atom reactions, di-n-propyl ether, (3.83 ± 0.05) × 10−10; di-n-propyl ether-d14, (2.84 ± 0.31) × 10−10; di-n-butyl ether, (5.15 ± 0.05) × 10−10; and di-n-butyl ether-d18, (4.03 ± 0.06) × 10−10. The rate constants for the di-n-propyl ether and di-n-butyl ether reactions are in agreement with literature data, and the deuterium isotope effects are consistent with H-atom abstraction being the rate-determining steps for both the OH radical and Cl atom reactions. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 425–431, 1999

Janet Arey

Papers

Rate constants for the gas-phase reactions of OH radicals with a series of C6-C14 alkenes at 299 +/- 2 K.

Kinetics and Nitro‐Products of the Gas‐Phase OH and NO3 Radical‐Initiated Reactions of Naphthalene‐d8, Fluoranthene‐d10, and Pyrene.

Kinetics of the gas‐phase reactions of NO3 radicals and O3 with 3‐methylfuran and the OH radical yield from the O3 reaction

Biogenic volatile organic compounds at Azusa and elevated sites during the 1997 Southern California Ozone Study

Rate constants for the reactions of OH radicals and Cl atoms with Di-n-Propyl ether and Di-n-Butyl ether and their deuterated analogs