Biogenic volatile organic compounds (BVOC) contribute significantly to the formation of ozone and secondary organic aerosol (SOA). The Model of Emissions of Gases and Aerosols from Nature (MEGANv2.02) is used to estimate emissions of isoprene, monoterpenes (MT), and sesquiterpenes (SQT) across the United States. Compared to the Biogenic Emission Inventory System (BEIS3.0), MEGANv2.02 estimates higher isoprene but lower MT emissions for July 2001 and January 2002. A sensitivity study of SQT and MT emission factors and algorithm parameters was conducted by assigning values to four plant functional types (PFTs) using both recent measurements and literature values. The standard deviations of the emissions factors within these PFTs were two to four times the averages because of the variation in experimental basal emissions rate data. More recently published SQT and MT basal emission rates are generally lower than those reported in the literature through 2004. With the new emissions factors, monthly average SQT emission rates for the contiguous United States are equal to 16% of the MT emissions during July and 9% of the emissions during January. The SQT emissions distribution is strongly influenced by the grass and crop PFT, for which SQT emissions data are quite limited.

Carbonyl compounds exist in the atmosphere as either gases or aerosols. Some of them are water soluble and known as oxidation products of biogenic and/or anthropogenic hydrocarbons. Five carbonyl compounds, glyoxal (GO), 4-oxopentanal (4-OPA), glycolaldehyde (GA), hydroxyacetone (HA) and methylglyoxal (MG) have been identified in a temporal series of 12 rain samples. The concentrations of the compounds in the samples were high at the beginning of the rain event and decreased with time to relatively low and fairly constant levels, indicating that the compounds were washed out from the atmosphere at the start of the rain event. Possibly, these compounds also existed in the cloud condensation nuclei (CCN). Wet deposition rates of the carbonyl compounds were calculated for nine samples collected during a 20 h period. The deposition rates ranged from 0 (4-OPA) to 1.2×10-1 mg C m-2 h-1 (MG) with the average of 2.9×10-2 mg C m-2 h-1. Production rates of isoprene oxidation products (GA, HA and MG) in the area surrounding the sampling site were estimated with a chemical box model. The deposition rates exceeded the production rates in most samples. This indicates that the rainfall causes a large net flux of the water soluble compounds from the atmosphere to the ground. Insoluble carbonyl compounds such as n-nonanal and n-decanal were expected to be present in the atmosphere, but were not detected in the rain during the sampling period, suggesting that an aerosol containing these insoluble compounds does not effectively act as a CCN. © 2006 Elsevier Ltd. All rights reserved.

Gaseous and particulate semi volatile carbonyls have been measured in urban air using an annular denuder sampling system. Three dicarbonyls, five aliphatic aldehydes and two hydroxy carbonyls were observed. Concentrations of other biogenic and anthropogenic volatile organic compounds (VOCs), SO2, CO, NO2 and particle concentration were also measured. Estimated gasaerosol equilibrium constants for the carbonyls showed an inverse correlation with the concentrations of anthropogenic pollutants such as benzene, isopentane and SO2. This suggests that the increase in the fraction of non-polar anthropogenic particles in the atmosphere could change the average property of the ambient aerosols and drive the gas particle equilibrium of the carbonyls to the gas phase. This trend is uncommon in remote forest air. In this study, we examined the factors controlling the equilibrium in the polluted atmosphere and show that there is a difference in gas-aerosol partition between polluted and clean air. Copyright 2005 by the American Geophysical Union.

A three-part study was conducted to quantify the impact of landscaped vegetation on air quality in a rapidly expanding urban area in the arid southeastern United States. The study combines in situ, plant-level measurements, a spatial emissions inventory, and a photochemical box model. Maximum plant-level basal emission rates were moderate: 18.1 μgC gdw-1 h-1 (Washingtonia spp., palms) for isoprene and 9.56 μgC gdw-1 h-1 (Fraxinus velutina, Arizona ash) for monoterpenes. Sesquiterpene emission rates were low for plant species selected in this study, with no measurement exceeding 0.1 μgC gdw-1 h-1. The high ambient temperatures combined with moderate plant-level emission factors resulted in landscape emission factors that were low (250-640 μgC m-2 h-1) compared to more mesic environments (e.g., the southeastern United States). The Regional Atmospheric Chemistry Mechanism (RACM) was modified to include a new reaction pathway for ocimene. Using measured concentrations of anthropogenic hydrocarbons and other reactive air pollutants (NOx, ozone), the box model employing the RACM mechanism revealed that these modest emissions could have a significant impact on air quality. For a suburban location that was downwind of the urban core (high NOx; low anthropogenic hydrocarbons), biogenic terpenes increased time-dependent ozone production rates by a factor of 50. Our study demonstrates that low-biomass density landscapes emit sufficient biogenic terpenes to have a significant impact on regional air quality. © 2009 Elsevier Ltd. All rights reserved.

Biogenic emission of sesquiterpene (SQT) and oxygenated SQT (OSQT) were measured from the dominant vegetation in a desert shrubland and urban area (Las Vegas, Nevada, U.S.A.), and at temperate forest sites at Niwot Ridge, Colorado, U.S.A., Tomakomai, Hokkaido, Japan and Tumbarumba, New South Wales, Australia. Additional measurements were conducted using greenhouse grown plants. The sampling technique, based on solid adsorbent preconcentration and liquid extraction, is suitable for measuring high molecular weight and low volatility compounds such as OSQTs. Fourteen SQT and OSQT (10 SQT and 4 OSQT) were identified in the field experiments. Total emission rates of SQTs and OSQTs varied from the detection limit to 7.6 μgC g-1h-1 (average: 0.74) and 3.7 μgC g-1h-1 (average: 0.31), respectively, and varied with plant species and location. Environmental conditions, including temperature and precipitation, appeared to influence emission rates. Canopy level emission of SQT and OSQT in Tomakomai were also estimated using an emission model. The emission rate of SQT and OSQT ranged from 72 to 710 μgC m-2h-1 (average, 460 in daytime) and from 38 to 370 μgC m-2h-1 (average, 240 in daytime), respectively. Their contributions can be very high in specific regions and seasons. Given the relatively high reactivity and secondary organic aerosol yields of SQTs and OSQTs, it is likely that these compounds influence atmospheric constituents in at least some areas. Copyright © 2009 by The Geochemical Society of Japan.

We have conducted a comprehensive observational study to determine the mixing ratios of atmospheric chemical species and total OH reactivity in central Tokyo, in order to diagnose the air quality during summer and winter 2007 and autumn 2009. Concentrations of over 70 reactive trace species were continuously measured throughout each season. The total OH reactivity was measured directly using a laser-induced pump and probe technique. The observed chemical species exhibited seasonal variations. There was a good correlation between NO and CO in winter, but not in summer. This indicates that during winter, vehicle exhaust provided a significant source of NO in central Tokyo, while photolysis of NO 2 was dominant in summer. Similar values (approximately 30s -1) for the averaged total OH reactivity were observed in both summer and autumn during the daytime. However, VOCs accounted for a larger percentage of the OH reactivity in summer, while NO x was more dominant in autumn. We find that photochemical processes leading to oxidant production via VOCs dominated OH removal in summer, while the production of nitric acid from the reaction between OH and NO 2 was dominant in autumn, by-passing the oxidant production pathways and resulting in reduced oxidant formation. © 2011 Elsevier Ltd.