Atmospheric Environment (v.41, #12)

Emissions of volatile organic compounds (VOCs) have multiple atmospheric implications and play many roles in plant physiology and ecology. Among these VOCs, growing interest is being devoted to a group of short-chain oxygenated VOCs (oxVOCs). Technology improvements such as proton transfer reaction-mass spectrometry are facilitating the study of these hydrocarbons and new data regarding these compounds is continuously appearing. Here we review current knowledge of the emissions of these oxVOCs by plants and the factors that control them, and also provide an overview of sources, sinks, and concentrations found in the atmosphere.The oxVOCs reviewed here are formic and acetic acids, acetone, formaldehyde, acetaldehyde, methanol, and ethanol. In general, because of their water solubility (low gas–liquid partitioning coefficient), the plant-atmosphere exchange is stomatal-dependent, although it can also take place via the cuticle. This exchange is also determined by atmospheric mixing ratios. These compounds have relatively long atmospheric half-lives and reach considerable concentrations in the atmosphere in the range of ppbv. Likewise, under non-stressed conditions plants can emit all of these oxVOCs together at fluxes ranging from 0.2 up to 4.8 μg(C)g−1(leaf dry weight)h−1 and at rates that increase several-fold when under stress.Gaps in our knowledge regarding the processes involved in the synthesis, emission, uptake, and atmospheric reactivity of oxVOCs precludes the clarification of exactly what is conditioning plant-atmosphere exchange—and also when, how, and why this occurs—and these lacunae therefore warrant further research in this field.
Keywords: Emission; oxVOCs; Formic acid; Acetic acid; Acetone; Formaldehyde; Acetaldehyde; Methanol; Ethanol; Biogenic;

Characteristics, determinants, and spatial variations of ambient fungal levels in the subtropical Taipei metropolis by Yi-Hua Wu; Chang-Chuan Chan; Carol Y. Rao; Chung-Te Lee; Hsiao-Hsien Hsu; Yueh-Hsiu Chiu; H. Jasmine Chao (2500-2509).
This study was conducted to investigate the temporal and spatial distributions, compositions, and determinants of ambient aeroallergens in Taipei, Taiwan, a subtropical metropolis. We monitored ambient culturable fungi in Shin-Jhuang City, an urban area, and Shi-Men Township, a rural area, in Taipei metropolis from 2003 to 2004. We collected ambient fungi in the last week of every month during the study period, using duplicate Burkard portable samplers and Malt Extract Agar. The median concentration of total fungi was 1339 colony-forming units m−3 of air over the study period. The most prevalent fungi were non-sporulating fungi, Cladosporium, Penicillium, Curvularia and Aspergillus at both sites. Airborne fungal concentrations and diversity of fungal species were generally higher in urban than in rural areas. Most fungal taxa had significant seasonal variations, with higher levels in summer. Multivariate analyses showed that the levels of ambient fungi were associated positively with temperature, but negatively with ozone and several other air pollutants. Relative humidity also had a significant non-linear relationship with ambient fungal levels. We concluded that the concentrations and the compositions of ambient fungi are diverse in urban and rural areas in the subtropical region. High ambient fungal levels were related to an urban environment and environmental conditions of high temperature and low ozone levels.
Keywords: Aeroallergens; Aerobiology; Bioaerosols; Culturable fungi; Subtropical;

Role of ammonia chemistry and coarse mode aerosols in global climatological inorganic aerosol distributions by Chao Luo; Charles S. Zender; Huisheng Bian; Swen Metzger (2510-2533).
We use an inorganic aerosol thermodynamic equilibrium model in a three-dimensional chemical transport model to understand the roles of ammonia chemistry and natural aerosols on the global distribution of aerosols. The thermodynamic equilibrium model partitions gas-phase precursors among modeled aerosol species self-consistently with ambient relative humidity and natural and anthropogenic aerosol emissions during the 1990s.Model simulations show that accounting for aerosol inorganic thermodynamic equilibrium, ammonia chemistry and dust and sea-salt aerosols improve agreement with observed SO4, NO3, and NH4 aerosols especially at North American sites. This study shows that the presence of sea salt, dust aerosol and ammonia chemistry significantly increases sulfate over polluted continental regions. In all regions and seasons, representation of ammonia chemistry is required to obtain reasonable agreement between modeled and observed sulfate and nitrate concentrations. Observed and modeled correlations of sulfate and nitrate with ammonium confirm that the sulfate and nitrate are strongly coupled with ammonium. SO4 concentrations over East China peak in winter, while North American SO4 peaks in summer. Seasonal variations of NO3 and SO4 are the same in East China. In North America, the seasonal variation is much stronger for NO3 than SO4 and peaks in winter.Natural sea salt and dust aerosol significantly alter the regional distributions of other aerosols in three main ways. First, they increase sulfate formation by 10–70% in polluted areas. Second, they increase modeled nitrate over oceans and reduce nitrate over Northern hemisphere continents. Third, they reduce ammonium formation over oceans and increase ammonium over Northern Hemisphere continents. Comparisons of SO4, NO3 and NH4 deposition between pre-industrial, present, and year 2100 scenarios show that the present NO3 and NH4 deposition are twice pre-industrial deposition and present SO4 deposition is almost five times pre-industrial deposition.
Keywords: Aerosol thermodynamics; Gas/aerosol partitioning; Ammonia chemistry; Global chemical transport model; Inorganic aerosol compositions;

The sensitivity of mesoscale simulations of land and sea breeze circulation on the south east coast in the Chennai region of India to boundary layer turbulence parameterizations is studied using the community based PSU/NCAR mesoscale model MM5. High-resolution simulations are carried out with nested domains. Four widely used boundary layer turbulence parameterization schemes are selected for the study. Two of these schemes (Blackadar (BK) and medium range forecast (MRF)) are simple first-order non-local schemes and the other two (Mellor–Yamada (MY) Eta planetary boundary layer (PBL) and Gayno–Seaman (GS)) are more complex 1.5 order local schemes that include a prognostic equation for turbulence kinetic energy. The other physics used in the model are identical. The micro-meteorological tower and flux observations, GP sonde and radiosonde observations from the study region are used to compare the simulated mean variables. In spite of differences in complexity, all the schemes show similar capability in simulating the boundary layer temperature, humidity and winds. The land–sea breeze circulation and internal boundary layer formation, which are special phenomena at the coastal site, could be simulated by all the schemes. The BK, MRF schemes produced boundary layers that are more mixed than those produced with the MY and GS schemes. While all the schemes underestimated surface sensible heat fluxes during stable night conditions they are reasonably simulated during daytime by MRF and BK schemes. Among the tested schemes, the BK scheme has reasonably produced the PBL height, humidity, wind fields and proves suitable for operational forecasting. The results suggest that there is little improvement in overall accuracy of predictions with more complex turbulence parameterizations.
Keywords: PBL parameterization; Mesoscale simulations; Land–sea breeze; MM5 model;

Personal exposure of children and adults to airborne benzene in four French cities by Norbert Gonzalez-Flesca; Eléna Nerriere; Nathalie Leclerc; Sébastien Le Meur; Hélène Marfaing; Alexis Hautemanière; Denis Zmirou-Navier (2549-2558).
Atmospheric concentrations of and personal exposure to benzene have been measured in four French metropolitan areas for 210 subjects over two seasons. Half of the volunteers were 6–13-year-old children. The adult subjects were non-smokers, not occupationally exposed and they live and work in the monitored areas. Measurements were performed using diffusive samplers followed by GC-FID analysis. The average values for ambient air concentrations (μg m−3) were: Rouen: 1.5; Île de France (Paris area): 1.6; Grenoble: 2.3 and Strasbourg: 2.6, showing that benzene concentrations in the ambient air of the four cities satisfy the requirements of the European Directive 2000/69EC of the European Parliament which stipulates a limit value of 5 μg m−3. However, the 48 h exposures measured were found to be between 2.7 and 3.5 times higher than ambient air concentrations. As a consequence, 60% of the subjects investigated, including children, were exposed to concentrations higher than the ambient air limit value. This work confirms that air monitoring data collected by fixed stations should be used with caution when assessing population exposure to benzene, especially given the influence of indoor sources and other polluted microenvironments where people spend part of their time.
Keywords: Benzene; Personal exposure; Children; Adults; Ambient air concentrations;

Observed trends in ambient concentrations of C2–C8 hydrocarbons in the United Kingdom over the period from 1993 to 2004 by G.J. Dollard; P. Dumitrean; S. Telling; J. Dixon; R.G. Derwent (2559-2569).
Hourly measurements of up to 26 C2–C8 hydrocarbons have been made at eight urban background sites, three urban-industrial sites, a kerbside and a rural site in the UK from 1993 onwards up until the end of December 2004. Average annual mean benzene and 1,3-butadiene concentrations at urban background locations have declined at about −20% per year and the observed declines have exactly mimicked the inferred declines in benzene and 1,3-butadiene emissions over the same period. Ninety-day rolling mean concentrations of ethylene, propylene, n- and i-butane, n- and i-pentane, isoprene and propane at urban and rural sites have also declined steadily by between −10% and −30% per year. Rolling mean concentrations of acetylene, 2- and 3-methylpentane, n-hexane, n-heptane, cis- and trans-but-2-ene, cis- and trans-pent-2-ene, toluene, ethylbenzene and o-, m- and p-xylene at a roadside location in London have all declined at between −14% and −21% per year. These declines demonstrate that motor vehicle exhaust catalysts and evaporative canisters have effectively and efficiently controlled vehicular emissions of hydrocarbons in the UK. Urban ethane concentrations arising largely from natural gas leakage have remained largely unchanged over this same period.
Keywords: C2–C8 hydrocarbons; VOCs; Trends; Urban measurements; Exhaust catalysts; Evaporative canisters;

Through the combined application of a speciated VOC emission inventory and an explicit chemical mechanism, a picture has been put together of the different contributions to photochemical ozone formation from 248 VOC emission source categories. The study has shown that the different VOC emission source categories show vastly different propensities for forming photochemical ozone as indexed by their photochemical ozone creation potentials (POCPs). POCPs range from close to zero for numerous processes, including halocarbon solvent usage, through to over 70 for diesel combustion and some reactive solvent and other product usage applications. The consequences of the large range in POCPs are highlighted for cost-effective VOC emission control strategies across north west Europe.
Keywords: Photochemical ozone formation; VOC emissions; Ozone control strategies;

Long-range transport of polycyclic aromatic hydrocarbons (PAHs) from the eastern Asian continent to Kanazawa, Japan with Asian dust by Shuji Tamamura; Tsutomu Sato; Yukie Ota; Xilong Wang; Ning Tang; Kazuichi Hayakawa (2580-2593).
Aerosol particles were collected for 1 year, starting in April 2003, in rural areas of Kanazawa, Ishikawa, Japan to understand the role of Asian dust as a long-range transporter of polycyclic aromatic hydrocarbons (PAHs). Three sampling intervals were designated in this study, namely: (1) Dust period 1 (March 11–19, 2003); (2) Dust period 2 (March 28, 2003–April 9, 2003); and (3) Dust period 3 (April 9, 2004–April 25, 2004). The Asian dust particles are predominantly in the coarse particle size range (2.1–11 μm). PAH analyses were performed separately on both the coarse and fine (<1.1 μm) particle ranges. Seasonal trends in PAH concentrations for coarse and fine particles showed that the Asian dust particles in Dust period 3 contained significant amounts of less-volatile PAHs such as benzo[a]pyrene (BaP) and benzo[g,h,i]perylene (BghiP). A kinetic model developed in this study shows that almost none of these PAHs would be accumulated on Asian dust particles in the atmosphere, due to their extremely slow adsorption rates. These PAHs would have to originate from PAH-polluted soil particles around industrialized areas. Back trajectory analyses suggest that the Asian dust in Dust period 3 came from loess regions around industrialized areas. This indicates that geologic materials play a significant role in the atmospheric circulation of PAHs.
Keywords: Asian dust; KOSA; PAHs; Long-range transport; Kinetic model; Mineral;

Development and application of a three-dimensional aerosol chemical transport model, PMCAMx by Timothy M. Gaydos; Rob Pinder; Bonyoung Koo; Kathleen M. Fahey; Gregory Yarwood; Spyros N. Pandis (2594-2611).
A three-dimensional chemical transport model (PMCAMx) is used to simulate PM mass and composition in the eastern United States for a July 2001 pollution episode. The performance of the model in this region is evaluated, taking advantage of the highly time and size-resolved PM and gas-phase data collected during the Pittsburgh Air Quality Study (PAQS). PMCAMx uses the framework of CAMx and detailed aerosol modules to simulate inorganic aerosol growth, aqueous-phase chemistry, secondary organic aerosol formation, nucleation, and coagulation. The model predictions are compared to hourly measurements of PM2.5 mass and composition at Pittsburgh, as well as to measurements from the AIRS and IMPROVE networks. The performance of the model for the major PM2.5 components (sulfate, ammonium, and organic carbon) is encouraging (fractional errors are in general smaller than 50%). Additional improvements are possible if the rainfall measurements are used instead of the meteorological model predictions. The modest errors in ammonium predictions and the lack of bias for the total (gas and particulate) ammonium suggest that the improved ammonia inventory used is reasonable. The significant errors in aerosol nitrate predictions are mainly due to difficulties in simulating the nighttime formation of nitric acid. The concentrations of elemental carbon (EC) in the urban areas are significantly overpredicted. This is a problem related to both the emission inventory but also the different EC measurement methods that have been used in the two measurement networks (AIRS and IMPROVE) and the actual development of the inventory. While the ability of the model to reproduce OC levels is encouraging, additional work is necessary to confirm that that this is due to the right reasons and not offsetting errors in the primary emissions and the secondary formation. The model performance against the semi-continuous measurements in Pittsburgh appears to be quite similar to its performance against daily average measurements in a wide range of stations across the Eastern US. This suggests that the skill of the model to reproduce the diurnal variability of PM2.5 and its major components is as good as its ability to reproduce the daily average values and also the significant value of high temporal resolution measurements for model evaluation.
Keywords: Chemical transport model; PM2.5; Eastern USA;

Trends in air concentration and deposition of mercury in the coastal environment of the North Sea Area by I. Wängberg; J. Munthe; T. Berg; R. Ebinghaus; H.H. Kock; C. Temme; E. Bieber; T.G. Spain; A. Stolk (2612-2619).
An evaluation of mercury observations from North Sea coastal stations during 1995–2002 has been performed. The mercury data originate from EMEP/OSPAR stations in Ireland, Netherlands, Germany, Norway and Sweden where mercury in precipitation and Total Gaseous Mercury (TGM) have been measured. A decreasing trend in mercury wet deposition is observed. The decrease is sufficiently large to be significant considering measurement precision and appears to occur at all the studied sites. The reduction in deposition is 10–30% when comparing the two periods 1995–1998 and 1999–2002. The trend is likely to be due to emission controls in Europe. In contrast, no decreasing trend in TGM could be observed during the same time periods. A plausible explanation is that the TGM concentration measured in the OSPAR area to a larger extent than before is dominated by the hemispherical background concentration of TGM.
Keywords: Atmospheric mercury; Mercury deposition; Long-range transport;

Continuous monitoring of carbon monoxide in a deep street canyon by Fabio Murena; Giuseppe Favale (2620-2629).
The results of a 1-week continuous monitoring campaign of carbon monoxide in a deep street canyon in the city of Naples are reported. CO was selected as a passive pollutant emitted by vehicle exhausts. The geometry of the canyon is: width W = 5.8 m and height H = 33 m (aspect ratio AR=H/W=5.7). The monitoring campaign was carried out from 14 to 20 June 2006. CO concentration level was measured at pedestrian level ( h = 2.5 m ) and roof top level ( h = 25 m ). In the same period traffic flow in the street canyon was manually measured and the CO emission rate from vehicle exhausts was evaluated using the COPERT procedure. Meteorological conditions (wind velocity and direction) are also reported and their effect on CO concentration level in the canyon is discussed. Due to its geometry the street canyon monitored may be considered almost ideal. The results show that the deep street canyon is a “hot spot” compared with roads with high traffic flows in the urban area of Naples, and that significant differences exist between concentration levels at pedestrian and roof top level. Some insights into the effect and relative importance of meteorological parameters on the air quality in the canyon are also given. The monitoring data collected have been made available on the web and can be used by other researchers to test air dispersion models.
Keywords: Deep street canyon; CO; Continuous monitoring; Air quality; Modelling;

A synthesis of AOT40-based response functions and critical levels of ozone for agricultural and horticultural crops by G. Mills; A. Buse; B. Gimeno; V. Bermejo; M. Holland; L. Emberson; H. Pleijel (2630-2643).
Crop-response data from over 700 published papers and conference proceedings have been analysed with the aim of establishing ozone dose-response functions for a wide range of European agricultural and horticultural crops. Data that met rigorous selection criteria (e.g. field-based, ozone concentrations within European range, full season exposure period) were used to derive AOT40-yield response functions for 19 crops by first converting the published ozone concentration data into AOT40 (AOT40 is the hourly mean ozone concentration accumulated over a threshold ozone concentration of 40 ppb during daylight hours, units ppm h). For any individual crop, there were no significant differences in the linear response functions derived for experiments conducted in the USA or Europe, or for individual cultivars. Three statistically independent groups were identified: ozone sensitive crops (wheat, water melon, pulses, cotton, turnip, tomato, onion, soybean and lettuce); moderately sensitive crops (sugar beet, potato, oilseed rape, tobacco, rice, maize, grape and broccoli) and ozone resistant (barley and fruit represented by plum and strawberry). Critical levels of a 3 month AOT40 of 3 ppm h and a 3.5 month AOT40 of 6 ppm h were derived from the functions for wheat and tomato, respectively.
Keywords: Ozone; Crops; Response functions; Critical levels; Yield; AOT40;

Atmospheric aerosols were collected in separate coarse (2–10 μm diameter) and fine (diameter less than 2 μm) size fractions at Rukomechi Research Station (16.1°S, 29.4°E), Zimbabwe, in the central part of southern Africa, from September 1994 to January 2000. The samples were analysed for the particulate mass (PM), black carbon, and 47 elements. The overall data set and the separate wet and dry season data sets were examined with absolute principal component analysis (APCA). Natural and anthropogenic aerosol sources were identified in both seasons, but the sources and their contributions to the total PM were found to vary between seasons and between size fractions. Crustal matter, sea salt (SS), a mixed biogenic (BIO) emission/biomass burning (BB) component, and a copper component were identified for the coarse aerosols during the wet season. APCA attributed 29% of the total wet season coarse PM to the mixed BIO/BB component, and 32% to SS. The copper component is likely due to the copper smelters in the Zambian Copperbelt. The dry season coarse PM originated from crustal matter, BB, BIO, and SS sources, with the major contribution (32%) coming from BB. Four components (crustal matter, BB, non-ferrous smelters, and SS) were identified for the fine particles for both the wet and dry seasons. The BB component provided the major contribution to the total fine PM, accounting for 44% and 79% in the wet and dry seasons, respectively. The relative contributions to the total PM (both fine and coarse) for all sources were greater in the dry season than the wet season, except for SS.
Keywords: Source apportionment; Principal component analysis; PIXE; Gent PM10 stacked filter unit; Multivariate analysis;

Emission factors of PAHs, methoxyphenols, levoglucosan, elemental carbon and organic carbon from simulated wheat and Kentucky bluegrass stubble burns by Ranil Dhammapala; Candis Claiborn; Jorge Jimenez; Jeffrey Corkill; Brian Gullett; Christopher Simpson; Michael Paulsen (2660-2669).
Emission factors (EFs) of pollutants from post-harvest agricultural burning are required for predicting downwind impacts of smoke and inventorying emissions. EFs of polycyclic aromatic hydrocarbons (PAH), methoxyphenols (MP), levoglucosan (LG), elemental carbon (EC) and organic carbon (OC) from wheat and Kentucky bluegrass (KBG) stubble burning were quantified in a US EPA test burn facility. The PAH and MP EFs for combined solid+gas phases are 17±8.2 mg kg−1 and 79±36 mg kg−1, respectively, for wheat and 21±15 mg kg−1 and 35±24 mg kg−1, respectively, for KBG. LG, particulate EC and artifact-corrected OC EFs are 150±130 mg kg−1, 0.35±0.16 g kg−1 and 1.9±1.1 g kg−1, respectively, for wheat and 350±510 mg kg−1, 0.63±0.056 g kg−1 and 6.9±0.85 g kg−1, respectively, for KBG. Positive artifacts associated with OC sampling were evaluated and remedied with a two-filter system. EC and OC accounted for almost two-thirds of PM2.5 mass, while LG accounted for just under 3% of the PM2.5 mass. Since EFs of these pollutants generally decreased with increasing combustion efficiency (CE), identifying and implementing methods of increasing the CEs of burns would help reduce their emissions from agricultural field burning. PAH, OC and EC EFs are comparable to other similar studies reported in literature. MP EFs appear dependent on the stubble type and are lower than the EFs for hard and softwoods reported in literature, possibly due to the lower lignin content in wheat and KBG.
Keywords: PAH; Methoxyphenol; Levoglucosan; Elemental carbon; Organic carbon; Emission factor; Combustion efficiency;

The influence of highway traffic on ambient nitrogen dioxide concentrations beyond the immediate vicinity of highways by Nicolas L. Gilbert; Mark S. Goldberg; Jeffrey R. Brook; Michael Jerrett (2670-2673).
The objective of these analyses was to determine whether highways significantly influence ambient concentrations of NO2 at distances greater than 200 m. NO2 was sampled for 14 consecutive days in May 2003 at 67 sites across Montréal, Canada. The association between logarithmic concentrations of NO2 and land-use variables was assessed using multiple regressions. Locations less than 100 m from the nearest highways were excluded, leaving 61 data points. Then, locations less than 200 m were excluded, leaving 55 data points. Excluding sampling locations located less than 100 or 200 m from the nearest highway did not substantially change the regression parameters. NO2 was still significantly associated with both the distance from nearest highway and the traffic count on the nearest highway. These findings indicate that the negative association found between distance from highways and NO2 concentration in several land-use regression studies in Europe and North America was not generated solely by the high concentrations found in the immediate vicinity of highways.
Keywords: Road traffic; Nitrogen dioxide; Land-use regression;

Seasonal and regional variations in precipitation chemistry in the Lake Taihu Basin, China by Liancong Luo; Boqiang Qin; Yuzhi Song; Longyuan Yang (2674-2679).
To evaluate seasonal and regional variations in precipitation chemistry in Lake Taihu Basin, 5 cities around the lake were selected for monthly collection of rainfall samples from July 2002 to June 2003. The analytical parameters included pH, cations (K+, Na+, Ca2+, Mg2+, NH 4 + ), anions (F, Cl, SO 4 2 - , NO 3 - ), total nitrogen (TN) and total phosphorus (TP). In descending order, concentrations (in meq L−1) of the ions in wet deposition can be ordered as SO 4 2 - > Ca 2 + > NH 4 + > NO 3 - >Cl>Na+>Mg2+>K+>F with concentratin percentages of 48.7%, 19.1%, 11.6%, 8.1%, 5.6%, 2.6%, 1.7%, 1.6% and 1%, respectively.Rainfall was seasonally variable, with high rates in spring and summer but low rates in autumn and winter, while ion concentrations followed the reverse seasonal cycle. To evaluate deposition rates (DR) of different elements, average DR of each ion was calculated from a simple model. Most of the highest DRs of these substances occurred in Suzhou and Wuxi, located east and north of Lake Taihu, which shows there was considerable variation over the 5 stations. This regional pattern reflects local emissions from industry and agriculture, and suggests that steps need to be taken by local governments for particle emission reductions. The estimated annual inputs of TN and TP over the lake are 4722 and 75 t, respectively, which accounts for around 16.5% and 7.3% of the annual total external inputs of these nutrients. Primary productivity in Lake Taihu associated solely with wet deposition of nitrogen to the lake was estimated to be 7.03×106  mol C day−1. These results suggest that wet deposition can have significant impacts on the trophic status of Lake Taihu and that attention to nutrients in precipitation should be included in the management of external nutrient loads to the lake.
Keywords: Precipitation chemistry; Wet deposition; Eutrophication; Riverine inputs; Lake Taihu;

New Directions: An unusual odor phenomenon in an urban atmosphere by S. Pentu Saheb; K.M. Phadke; G.H. Pandya (2680-2681).