Atmospheric Environment (v.41, #8)

The purpose of this study was to characterize size distributions of atmospheric polycyclic aromatic hydrocarbons (PAHs) with 4–6 rings at the roadside in Ho Chi Minh City, Vietnam. Ten PAHs (fluoranthene, pyrene, triphenylene, benzo[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, benzo[ghi]perylene and indeno[1,2,3-cd]pyrene) in atmospheric particulate matters (PM) at the roadside were measured in the dry and rainy seasons in 2005 at Ho Chi Minh City, using a low-pressure cascade impactor. The PM were separated into nine fractions by their aerodynamic diameter, i.e. >9.0, 9.0–5.8, 5.8–4.7, 4.7–3.3, 3.3–2.1, 2.1–1.1, 1.1–0.7, 0.7–0.4 and <0.4 μm (a final filter). PAHs were analyzed by high-performance liquid chromatography with fluorescence detection. Total PAHs measured were higher in the rainy season than in the dry season. The mass of coarse particles occupied a higher fraction than that of fine particles in both seasons. Total PAHs were mainly concentrated in particles with aerodynamic diameter smaller than 0.4 μm. The particle size distributions of PAHs investigated were bi-modal with a peak in fine particle mode (<2.1 μm) and another peak in coarse particle mode (>2.1 μm). Generally, 5,6-ring PAHs associated mainly with fine particles and 4-ring PAHs spread out in both fine and coarse particles.
Keywords: PAHs; Size distribution; Particulate matters; Seasonal trend; Roadside; Asia;

Under fair weather conditions, a weak electric field exists between negative charge induced on the surface of plants and positive charge in the air. This field is magnified around points (e.g. stigmas) and can reach values up to 3×106  V m−1. If wind-dispersed pollen grains are electrically charged, the electrostatic force (which is the product of the pollen's charge and the electric field at the pollen's location) could influence pollen capture. In this article, we report measurements of the electrostatic charge carried by wind-dispersed pollen grains. Pollen charge was measured using an adaptation of the Millikan oil-drop experiment for seven anemophilous plants: Acer rubrum, Cedrus atlantica, Cedrus deodara, Juniperus virginiana, Pinus taeda, Plantago lanceolata and Ulmus alata. All species had charged pollen, some were positive others negative. The distributions (number of pollen grains as a function of charge) were bipolar and roughly centered about zero although some distributions were skewed towards positive charges. Most pollen carried small amounts of charge, 0.8 fC in magnitude, on average. A few carried charges up to 40 fC. For Juniperus, pollen charges were also measured in nature and these results concurred with those found in the laboratory. For nearly all charged pollen grains, the likelihood that electrostatics influence pollen capture is evident.
Keywords: Electrostatic field; Fair-weather electricity; Pollen; Wind pollination;

During fair-weather conditions, a 100 V m−1 electric field exists between positive charge suspended in the air and negative charge distributed on the surfaces of plants and on the ground. The fields surrounding plants are highly complex reaching magnitudes up to 3×106  V m−1. These fields possibly influence the capture of charged wind-dispersed pollen grains. In this article, we model the electric fields around grounded conductive spherical “plants” and then estimate the forces and resulting trajectories of charged pollen grains approaching the plants. Pollen grain capture depends on many factors: the size, density, and charge of the pollen; the size and location of the plant reproductive structures; as well as wind speed, ambient electric field magnitude, and air viscosity. Electrostatic forces become increasingly important as pollen grain charge increases and pollen grain size (mass) decreases. A positively charged pollen grain is attracted to plants, while a negatively charged pollen grain is repelled. The model suggests that a pollen grain (10 μm radius, carrying a positive charge of 1 fC) is captured if passing within 2 mm of the plant. A similar negatively charged pollen grain is repelled and frequently uncapturable. The importance of electrostatic forces in pollen capture is limited by wind, becoming virtually irrelevant at high wind speeds (e.g. 10 m s−1). However, during light wind conditions (e.g. 1 m s−1), atmospheric electricity may be a significant factor in the capture of wind-dispersed pollen.
Keywords: Atmospheric electricity; Electrostatic charge; Electrostatic field; Particle capture; Wind pollination;

Comparing field performances of denuder techniques in the high Arctic by Antonietta Ianniello; Harry J. Beine; Matthew S. Landis; Robert K. Stevens; Giulio Esposito; Antonio Amoroso; Ivo Allegrini (1604-1615).
A field evaluation between two annular denuder configurations was conducted during the spring of 2003 in the marine Arctic at Ny-Ålesund, Svalbard. The IIA annular denuder system (ADS) employed a series of five single-channel annular denuders, a cyclone and a filter pack to discriminate between gas and aerosol species, while the EPA-Versatile Air Pollution Sampler (VAPS) configuration used a single multi-channel annular denuder to protect the integrity of PM2.5 sample filters by collecting acidic gases. We compared the concentrations of gaseous nitric acid (HNO3), nitrous acid (HONO), sulfur dioxide (SO2) and hydrochloric acid (HCl) measured by the two systems. Results for HNO3 and SO2 suggested losses of gas phase species within the EPA-VAPS inlet surfaces due to low temperatures, high relative humidities, and coarse particle sea-salt deposition to the VAPS inlet during sampling. The difference in HNO3 concentrations (55%) between the two data sets might also be due to the reaction between HNO3 and NaCl on inlet surfaces within the EPA-VAPS system. Furthermore, we detected the release of HCl from marine aerosol particles in the EPA-VAPS inlet during sampling contributing to higher observed concentrations. Based on this work we present recommendations on the application of denuder sampling techniques for low-concentration gaseous species in Arctic and remote marine locations to minimize sampling biases. We suggest an annular denuder technique without a large surface area inlet device in order to minimize retention and/or production of gaseous atmospheric pollutants during sampling.
Keywords: Arctic; Atmospheric chemistry; Annular denuder; Multi-channel denuder;

Correction in aerosol mass concentration measurements with humidity difference between ambient and instrumental conditions by Gerry Bagtasa; Nobuo Takeuchi; Shunsuke Fukagawa; Hiroaki Kuze; Suekazu Naito (1616-1626).
The influence of humidity is considered on the concentration of the suspended particulate matter (SPM) measured with a β-ray counter. The humidity condition inside a small observatory where the counter is located is, in general, different from the ambient condition outside the observatory. From the measured values, the ambient SPM concentration is derived considering the hygroscopic effect of common aerosol species of sea salt (SS), (NH4)2SO4, NH4NO3 and NaNO3. In a case study conducted during September 2005, temperature and humidity were measured both inside and outside the observatory. The average value of the relative humidity is 48% for inside and 78% for outside, resulting in approximately 53% larger SPM mass concentration after the correction. Accordingly, the value of mass extinction efficiency, which is given by the ratio between the optically measured extinction coefficient and the mass concentration, becomes lower after the correction.
Keywords: Suspended particulate matter; Mass concentration; Mass extinction efficiency; Hygroscopic aerosol; Portable automated lidar;

To evaluate the tropical wetlands contribution to the methane (CH4) burden better, field campaigns were performed during 2004 and 2005 near the Miranda River, in five sites inside the Brazilian Pantanal region. The CH4 fluxes were determined using the static chamber technique. Environmental variables that may affect CH4 emissions, as the water depth, the water and air temperatures were also measured. The overall average of the 320 individual CH4 flux measurements made between March/2004 and March/2005 was 142±314 mg CH4  m−2  d−1, which is a value near the ones observed in other tropical flooded regions. About 47% of the fluxes measurements presented nonlinear increases in the chamber concentrations, which were assumed to be linked to CH4 losses through bubbles. The bubble flux represented about 90% of the total CH4 losses in the measurements and ranged from 1 to 2187 mg CH4  m−2  d−1 with an average of 292±410 mg CH4  m−2  d−1 (median: 153 mg CH4  m−2  d−1). The diffusive flux ranged from 1 to 124 mg CH4  m−2  d−1, with an average of 10±17 mg CH4  m−2  d−1 (median: 5 mg CH4  m−2  d−1). The fluxes from lakes were smaller than those observed in the floodplains, where the flooding was more dependent on the seasonal cycle. The diffusive flux showed a slight, but not statistically significant seasonal variation, following the seasonal variation of the flooding of the Pantanal region. A rough estimative of the total annual CH4 emission shows that the contribution of the Pantanal is about 3.3 Tg CH4  yr−1, which represents about 3.3% of the total CH4 emissions estimated to be originated in wetlands ecosystems. It may be a conservative estimate, which may present a large interannual variation, since it was obtained during one of the lowest flood of the Pantanal in recent years.
Keywords: Methane emission; Wetlands; Pantanal; Greenhouse gases; Floodplain; Seasonal variability;

Multi-year records of MODIS, micro-pulse lidar (MPL), and aerosol robotic network (AERONET) Sun/sky radiometer measurements were analyzed to investigate the seasonal, monthly and geographical variations of columnar aerosol optical properties over east Asia. Similar features of monthly and seasonal variations were found among the measurements, though the observational methodology and periods are not coincident. Seasonal and monthly cycles of MODIS-derived aerosol optical depth (AOD) over east Asia showed a maximum in spring and a minimum in autumn and winter. Aerosol vertical extinction profiles measured by MPL also showed elevated aerosol loads in the middle troposphere during the spring season. Seasonal and spatial distributions were related to the dust and anthropogenic emissions in spring, but modified by precipitation in July–August and regional atmospheric dispersion in September–February. All of the AERONET Sun/sky radiometers utilized in this study showed the same seasonal and monthly variations of MODIS-derived AOD. Interestingly, we found a peak of monthly mean AOD over industrialized coastal regions of China and the Yellow Sea, the Korean Peninsula, and Japan, in June from both MODIS and AERONET Sun/sky radiometer measurements. Especially, the maximum monthly mean AOD in June is more evident at the AERONET urban sites (Beijing and Gwangju). This AOD June maximum is attributable to the relative contribution of various processes such as stagnant synoptic meteorological patterns, secondary aerosol formation, hygroscopic growth of hydrophilic aerosols due to enhanced relative humidity, and smoke aerosols by regional biomass burning.
Keywords: MODIS; Lidar; AERONET Sun/sky radiometer; Seasonal and monthly variations; AOD;

Night-time tropospheric chemistry of the unsaturated alcohols (Z)-pent-2-en-1-ol and pent-1-en-3-ol: Kinetic studies of reactions of NO3 and N2O5 with stress-induced plant emissions by Christian Pfrang; Maria T. Baeza Romero; Beatriz Cabanas; Carlos E. Canosa-Mas; Florentina Villanueva; Richard P. Wayne (1652-1662).
The night-time tropospheric chemistry of two stress-induced volatile organic compounds (VOCs), (Z)-pent-2-en-1-ol and pent-1-en-3-ol, has been studied at room temperature. Rate coefficients for reactions of the nitrate radical (NO3) with these pentenols were measured using the discharge-flow technique. Because of the relatively low volatility of these compounds, we employed off-axis continuous-wave cavity-enhanced absorption spectroscopy for detection of NO3 in order to be able to work in pseudo first-order conditions with the pentenols in large excess over NO3. The rate coefficients were determined to be (1.53±0.23)×10−13 and (1.39±0.19)×10−14  cm3  molecule−1  s−1 for reactions of NO3 with (Z)-pent-2-en-1-ol and pent-1-en-3-ol. An attempt to study the kinetics of these reactions with a relative-rate technique, using N2O5 as source of NO3 resulted in significantly higher apparent rate coefficients. Performing relative-rate experiments in known excesses of NO2 allowed us to determine the rate coefficients for the N2O5 reactions to be (5.0±2.8)×10−19  cm3  molecule−1  s−1 for (Z)-pent-2-en-1-ol, and (9.1±5.8)×10−19  cm3  molecule−1  s−1 for pent-1-en-3-ol. We show that these relatively slow reactions can indeed interfere with rate determinations in conventional relative-rate experiments.
Keywords: Atmosphere; Pentenol; Nitrate; Radical; Rate;

Aqueous phase methylation as a potential source of methylmercury in wet deposition by Chad R. Hammerschmidt; Carl H. Lamborg; William F. Fitzgerald (1663-1668).
The source of monomethylmercury (MMHg) in wet deposition is unknown. Volatilization of gaseous MMHg, evasion and demethylation of dimethylmercury, and methylation of Hg0 have been either proposed or tested unsuccessfully as potential sources. Here, we show that MMHg in precipitation, sampled across a wide geographical range in North America, is related positively to an operationally defined and measured reactive Hg species (HgR), but connected weakly to total Hg. The mean molar ratio of MMHg:HgR measured in continental precipitation (0.025±0.006) is comparable to the MMHg:Hg(II) ratio estimated from first-order rate constants for acetate-mediated Hg methylation and MMHg photolysis (0.025±0.002). This suggests MMHg may be formed in the atmosphere through a reaction between labile Hg(II) complexes and an unknown methylating agent(s), potentially acetate or similar molecules. Availability of Hg(II) appears to limit the reaction, and accordingly, increased atmospheric loadings of Hg could lead to enhanced MMHg in precipitation.
Keywords: Mercury; Abiotic; Atmosphere; Precipitation; Photodecomposition;

Mercury wet deposition is dependent on both the scavenging of divalent reactive gaseous mercury (RGM) and atmospheric particulate mercury (Hg(p)) by precipitation. Estimating the contribution of precipitation scavenging of RGM and Hg(p) is important for better understanding the causes of the regional and seasonal variations in mercury wet deposition. In this study, the contribution of Hg(p) scavenging was estimated on the basis of the scavenging ratios of other trace elements (i.e., Cd, Cu, Mn, Ni, Pb and V) existing entirely in particulate form. Their wet deposition fluxes and concentrations in air, which were measured concurrently from April 2004 to March 2005 at 10 sites in Japan, were used in this estimation. The monthly wet deposition flux of mercury at each site correlated with the amount of monthly precipitation, whereas the Hg(p) concentrations in air tended to decrease during summer. There was a significant correlation (P<0.001) among the calculated monthly average scavenging ratios of trace elements, and the values in each month at each site were similar. Therefore, it is assumed the monthly scavenging ratio of Hg(p) is equivalent to the mean value of other trace elements. Using this scavenging ratio (W), the wet deposition flux (F) due to Hg(p) scavenging in each month was calculated by F=WKP, where K and P are the Hg(p) concentration and amount of precipitation, respectively. Relatively large fluxes due to Hg(p) scavenging were observed at a highly industrial site and at sites on the Japan Sea coast, which are strongly affected by the local sources and the long-range transport from the Asian continent, respectively. However, on average, at the 10 sites, the contribution of Hg(p) scavenging to the annual mercury deposition flux was 26%, suggesting that mercury wet deposition in Japan is dominated by RGM scavenging. This RGM should originate mainly from the in situ oxidation of Hg0 in the atmosphere.
Keywords: Scavenging ratio; Reactive gaseous mercury; Amount of precipitation; Trace elements; Asian continent;

Due to the high temporal and spatial variability of N2O fluxes, estimates of N2O emission from temperate forest ecosystems are still highly uncertain, particularly at larger scales. Although highest N2O emissions with up to 7.0 kg N ha−1  yr−1 were mainly reported for soils affected by stagnant water, most of the reported gas flux measurements were performed at forest sites with well-aerated soils yielding mostly to low mean annual emission rates less than 1.0 kg N ha−1  yr−1. This study compares N2O fluxes from upland (Cambisols) and temporally water-logged (Gleysols, Histosols) soils of the Central Black Forest (South-West Germany) over a period of 2 yr. Mean annual N2O fluxes from investigated soils ranged between 0.2 and 3.9 kg N ha−1  yr−1. The fluxes showed a large variability between the different soil types. Emissions could be clearly ranked in the following order: Cambisols (0.26–0.75 kg N ha−1  yr−1)<Gleysols (1.37–2.68 kg N ha−1  yr−1)<Histosol (3.66–3.95 kg N ha−1  yr−1). Although the Cambisols cover two-thirds of the investigated area, only about half of the overall N2O is emitted from this soil type. Therefore, regional or national N2O fluxes from temperate forest soils are underestimated if soils characterised by intermediate aeration conditions are disregarded.
Keywords: Nitrous oxide emission; Organic soils; Mineral soils; Norway spruce; Black forest;

Evaluating the use of outputs from comprehensive meteorological models in air quality modeling applications by Vlad Isakov; Akula Venkatram; Jawad S. Touma; Darko Koračin; Tanya L. Otte (1689-1705).
Currently used dispersion models, such as the AMS/EPA Regulatory Model (AERMOD), process routinely available meteorological observations to construct model inputs. Thus, model estimates of concentrations depend on the availability and quality of meteorological observations, as well as the specification of surface characteristics at the observing site. We can be less reliant on these meteorological observations by using outputs from prognostic models, which are routinely run by the National Oceanic and Atmospheric Administration (NOAA). The forecast fields are available daily over a grid system that covers all of the United States. These model outputs can be readily accessed and used for dispersion applications to construct model inputs with little processing. This study examines the usefulness of these outputs through the relative performance of a dispersion model that has input requirements similar to those of AERMOD. The dispersion model was used to simulate observed tracer concentrations from a Tracer Field Study conducted in Wilmington, California in 2004 using four different sources of inputs: (1) onsite measurements; (2) National Weather Service measurements from a nearby airport; (3) readily available forecast model outputs from the Eta Model; and (4) readily available and more spatially resolved forecast model outputs from the MM5 prognostic model. The comparison of the results from these simulations indicate that comprehensive models, such as MM5 and Eta, have the potential of providing adequate meteorological inputs for currently used short-range dispersion models such as AERMOD.
Keywords: Prognostic meteorological models; Dispersion modeling; Model evaluation; Tracer experiment; Thermal internal boundary layer;

Air concentrations and wet deposition of major inorganic ions at five non-urban sites in China, 2001–2003 by Wenche Aas; Min Shao; Lei Jin; Thorjørn Larssen; Dawei Zhao; Renjun Xiang; Jinhong Zhang; Jinsong Xiao; Lei Duan (1706-1716).
Air and precipitation measurements at five sites were undertaken from 2001 to 2003 in four different provinces in China, as part of the acid rain monitoring program IMPACTS. The sites were located in Tie Shan Ping (TSP) in Chongqing, Cai Jia Tang (CJT) in Hunan, Lei Gong Shan (LGS) and Liu Chong Guan (LCG) in Guizhou and Li Xi He (LXH) in Guangdong. The site characteristics are quite varied with TSP and LCG located relatively near big cites while the three others are situated in more regionally representative areas. The distances to urban centres are reflected in the air pollution concentrations, with annual average concentrations of SO2 ranging from 0.5 to above 40 μg S m−3. The main components in the airborne particles are (NH4)2SO4 and CaSO4. Reduced nitrogen has a considerably higher concentration level than oxidised nitrogen, reflecting the high ammonia emissions from agriculture. The gas/particle ratio for the nitrogen compounds is about 1:1 at all the three intensive measurement sites, while for sulphur it varies from 2.5 to 0.5 depending on the distance to the emission sources. As in air, the predominant ions in precipitation are sulphate, calcium and ammonium. The volume weighted annual concentration of sulphate ranges from about 70 μeq l−1 at the most rural site (LGS) to about 200 μeq l−1 at TSP and LCG. The calcium concentration ranges from 25 to 250 μeq l−1, while the total nitrogen concentration is between 30 and 150 μeq l−1; ammonium is generally twice as high as nitrate. China's acid rain research has traditionally been focused on urban sites, but these measurements show a significant influence of long range transported air pollutants to rural areas in China. The concentration levels are significantly higher than seen in most other parts of the world.
Keywords: Air; Aerosols; Precipitation; Acid rain; IMPACTS;

The UN Global Mercury Assessment (GMA) estimates that atmospheric emissions of mercury from Australian stationary combustion sources were 97.0 tonnes for the year of 1995. This is more than 90% of the estimated emissions from stationary combustion for the whole of North America, and seems abnormally high for a country with a population of around 20 million, in spite of the fact that most of Australia's stationary energy supply is provided by coal. It is also significantly larger than previous estimates of mercury emissions from Australian sources. New estimates of Australian mercury emissions from stationary energy sources, based on both a top down and bottom up approach, are presented. These estimates can be reconciled for black coal fired power stations, but suggest that the bottom up approach (the Australian National Pollutant Inventory) significantly under-estimates emissions from brown coal fired plant, if mercury capture efficiencies in these plants are low, as observed for lignite-fired plant. The major uncertainties in these estimates are the coal mercury content in coals burnt in Australian power stations, and the mercury capture efficiency in particulate control devices used at these stations. Based on these estimates, Australian emissions of mercury from stationary energy are currently 2–8 tonnes/year, significantly lower than the GMA estimate.
Keywords: Mercury; Coal combustion; Emission Inventory;

A sensitivity study of separation distances calculated with the Austrian Odour Dispersion Model (AODM) by Martin Piringer; Erwin Petz; Inga Groehn; Günther Schauberger (1725-1735).
The Austrian Odour Dispersion Model (AODM) is a Gaussian model adapted for the prediction of odour sensation. It estimates the daily and seasonal variation of the odour emission, the average, ambient odour concentration and the momentary (peak) concentration for the time-interval of a single human breath (approx. 5 s). Peak concentrations, further downwind, are modified by use of an exponential attenuation function for which the ratios of the standard deviations of the wind components to the average wind speed have either to be taken from the literature or to be calculated, e.g. from ultrasonic anemometer data.AODM calculates direction-dependent separation distances for a combination of odour threshold and exceedence probability, which are a function of the prevailing wind velocity and atmospheric stability conditions. Meteorological time series from one site in Styria in southern Austria and one site in the Austrian flatlands, North of the Alps, both rural, are used for a sensitivity study of separation distances. One aspect is, how two different schemes to determine atmospheric stability influence the separation distances. Another source of uncertainty of the calculated separation distances results from the use of measured or literature values for the ratios mentioned above. Decisions on which schemes or ratios to be used have a decisive influence on the separation distances.
Keywords: Odour; Stability class; Peak-to-mean ratio; Separation distance; Gauss model;

A proton transfer reaction mass spectrometry based system for determining plant uptake of volatile organic compounds by Akira Tani; Shungo Kato; Yoshizumi Kajii; Michael Wilkinson; Sue Owen; Nick Hewitt (1736-1746).
In order to evaluate the contribution that higher plants make to the removal of volatile organic compounds from the atmosphere, a measurement system consisting of a proton transfer reaction mass spectrometer (PTR-MS), CO2 analyzer, diffusion devise and leaf enclosure was established. The uptake of VOCs by Golden Pothos (Epipremnum aureum) was investigated. The overall relative error associated with measurements made using this system was <2.2% when a Golden Pothos leaf was exposed to 75–750 ppbv of methyl isobutyl ketone (MIBK). Even at the lowest MIBK concentration, more than 2.2% of the inflowing VOC was lost to the leaf, representing a detectable and positive MIBK uptake rate by the plant. The results of the investigation were compared with a measurement system based on gas chromatography analysis and it was shown that the use of a PTR-MS based system can significantly increase the certainties in determining the rate of VOC uptake by plants.
Keywords: Proton transfer reaction mass spectrometer; VOC; Uptake; Methyl isobutyl ketone;

Real-world emission factors of fifteen carbonyl compounds measured in a Hong Kong tunnel by K.F. Ho; Steven Sai Hang Ho; Y. Cheng; S.C. Lee; Jian Zhen Yu (1747-1758).
Real-world vehicle emissions of carbonyls were determined in summer and winter of 2003 at the Shing Mun Tunnel, Hong Kong. Fifteen carbonyl species have been analyzed in this study. The total measured carbonyls emission factors ranged from 21.7 to 68.9 mg veh−1  km−1 among different measurement periods, with an average of 35.8±11.9 mg veh−1  km−1. Higher carbonyl emissions were found to be associated with a high proportion of diesel-fueled vehicles. Total measured carbonyl emissions from Diesel-fueled Vehicle (DV, 71.5 mg veh−1  km−1) were about 7 times higher than those from Non-Diesel-fueled Vehicle (NDV, 10 mg veh−1  km−1). The five carbonyls with the largest DV emission factor were, in decreasing order, formaldehyde (38.3 mg veh−1  km−1), acetaldehyde (11.4 mg veh−1  km−1), acetone (5.3 mg veh−1  km−1), crotonaldehyde (5.2 mg veh−1  km−1) and benzaldehyde (2.0 mg veh−1  km−1). These five carbonyl compounds together accounted for 87% of the sum of all DV carbonyl emission factors. For NDV, the five most abundant carbonyls in NDV emission at the tunnel were, in decreasing order, formaldehyde (3.5 mg veh−1  km−1), acetone (1.8 mg veh−1  km−1), methyl ethyl ketone (1.6 mg veh−1  km−1), m,p-tolualdehyde (1.0 mg veh−1  km−1) and acetaldehyde (mg veh−1  km−1). They accounted for 85% of the sum of all NDV carbonyl emission factors.
Keywords: Carbonyl compounds; Tunnel; Emission factor; Ozone formation; Hong Kong;

Development of particle number size distribution near a major road in Helsinki during an episodic inversion situation by Veli-Matti Kerminen; Tuomo A. Pakkanen; Timo Mäkelä; Risto E. Hillamo; Markus Sillanpää; Topi Rönkkö; Annele Virtanen; Jorma Keskinen; Liisa Pirjola; Tareq Hussein; Kaarle Hämeri (1759-1767).
The influence of traffic on urban air quality is highest at low wind speeds and the presence of a temperature inversion. By relying on detailed aerosol measurements conducted simultaneously at two distances close to a major road, we studied one such episode encountered in Helsinki, Finland, during the wintertime. The observed episode was characterized by exceptionally weak dilution of traffic emissions, with particle number concentration decreasing by no more than 10–30% between 9 and 65 m distances from the road. During the nighttime with relatively minor traffic flow, dilution and particle growth by vapor condensation were found to be the dominant processes in this road-to-ambient evolution stage. The latter process shifted a significant fraction of nucleation mode particles to sizes >30 nm diameter, modifying thereby the shape of the particle number size distribution. During the rush hours in the morning, particle number concentrations were elevated by approximately an order of magnitude compared with nighttime, such that also the self-coagulation of nucleation mode particles became important. Our study demonstrates that under suitable meteorological conditions (low wind speeds coupled with temperature inversions), traffic emissions are able to affect submicron particle number concentrations over large areas around major roads and may be a dominant source of ultrafine particles in the urban atmosphere. Under conditions characterized by exceptionally slow mixing, simultaneous processing of ultrafine (nucleation and Aitken mode) particles by dilution, self- and inter-modal coagulation, as well as by condensation and evaporation seriously questions the applicability of particle number emission factors, derived from the measurements at few tens of meters from the roadside.
Keywords: Traffic exhaust; Particle number; Dispersion; Condensation; Coagulation;

Effect of particle phase oligomer formation on aerosol growth by M. Vesterinen; K.E.J. Lehtinen; M. Kulmala; A. Laaksonen (1768-1776).
We study theoretically the effect of oligomer formation on secondary organic aerosol (SOA) growth following ozonolysis of α -pinene. Our goal is to show qualitatively, using a simplified condensational growth model, that the formation of involatile oligomers can induce the condensation growth of aerosols even if the secondary organic species formed in the oxidation reactions are rather volatile and therefore poorly condensable. The closed system studied consists of a single effective gas-phase oxidation product, and a seed aerosol population consisting of monodisperse ammonium sulphate particles. The oligomer formation is described as an effective dimerisation reaction between the monomers in the aerosol phase. By varying the dimerisation constant until our model results match the results from earlier smog-chamber studies, we are able to make order-of-magnitude estimations of the unknown dimerisation rates needed to induce the observed SOA growth. We also make model simulations using atmospheric α -pinene and ozone concentrations, and find that the effective dimerisation rate inducing SOA growth in the atmosphere has to be considerably higher than that causing SOA growth in smog-chamber conditions.
Keywords: Oligomer; Monoterpene; Dimerisation; SOA;

Air pollution reduction via use of green energy sources for electricity and hydrogen production by Mikhail Granovskii; Ibrahim Dincer; Marc A. Rosen (1777-1783).
The implementation of renewable wind and solar energy sources instead of fossil fuels to produce such energy carriers as electricity and hydrogen facilitates reductions in air pollution emissions. Unlike from traditional fossil fuel technologies, air pollution emissions from renewable technologies are associated mainly with the construction of facilities. With present costs of wind and solar electricity, it is shown that, when electricity from renewable sources replaces electricity from natural gas, the cost of air pollution emission abatement is more than ten times less than the cost if hydrogen from renewable sources replaces hydrogen produced from natural gas. When renewable-based hydrogen is used instead of gasoline in a fuel cell vehicle, the cost of air pollution emissions reduction approaches the same value as for renewable-based electricity only if the fuel cell vehicle efficiency exceeds significantly (i.e., by about two times) that of an internal combustion vehicle. The results provide the basis for a useful approach to an optimal strategy for air pollution mitigation.
Keywords: Air pollution; Emissions; Renewable energy; Hydrogen; Electricity; Life cycle assessment;

Investigation into the use of the CUSUM technique in identifying changes in mean air pollution levels following introduction of a traffic management scheme by Benjamin Barratt; Richard Atkinson; H. Ross Anderson; Sean Beevers; Frank Kelly; Ian Mudway; Paul Wilkinson (1784-1791).
There is an increasing need for statistical techniques to identify and quantify the effects of traffic management schemes on ambient pollution levels. Cumulative sum (CUSUM) charts have been used extensively in industrial process control to detect deviations in production parameters from pre-determined values. This study investigates the use of the CUSUM procedure to identify change in ambient air pollution levels following the introduction of a traffic management scheme at a specific location in Central London.The CUSUM methods of Lucas first compute the standardised deviations of time series observations from the desired process mean. These are accumulated over time to compute the CUSUM at each time point.Data for the analysis were taken from a kerbside monitoring site on Marylebone Road, a six lane trunk route in Central London. In August 2001 the lane adjacent to the monitoring site was designated as a permanent bus lane. The CUSUM analysis clearly identifies a sustained decrease in carbon monoxide concentrations beginning in 2002. However, seasonality and other factors precluded precise characterisation of the timing of the change. When the analysis was repeated using a reference mean that extrapolated the pre-intervention trend in carbon monoxide concentrations, the CUSUM chart no longer identified a sustained decrease.CUSUM appears to offer a simple and rapid method for identifying sustained changes in pollution levels, but the range of confounding influences on carbon monoxide concentrations, most notably underlying trends, seasonality and independent interventions, complicate its interpretation. Its application in assessing the presence or timing of a stepped change in pollution or similar environmental time series data is recommended in its basic form only where the predicted change is large by comparison with other independent influences. The authors believe that further development of the technique beyond this initial study is worthwhile in order to improve the technique's sensitivity.
Keywords: CUSUM; Traffic management; Air pollution; Air quality management;

Gas-phase rate coefficients for the reactions of NO3, OH and O3 with α,β-unsaturated esters and ketones: Structure−activity relations (SARs) by Christian Pfrang; Martin D. King; Carlos E. Canosa-Mas; Mark Flugge; Richard P. Wayne (1792-1802).
Gas-phase rate coefficients for the atmospherically important reactions of NO3, OH and O3 are predicted for 55 α,β-unsaturated esters and ketones. The rate coefficients were calculated using a correlation described previously [Pfrang, C., King, M.D., C. E. Canosa-Mas, C.E., Wayne, R.P., 2006. Atmospheric Environment 40, 1170–1179]. These rate coefficients were used to extend structure–activity relations for predicting the rate coefficients for the reactions of NO3, OH or O3 with alkenes to include α,β-unsaturated esters and ketones. Conjugation of an alkene with an α,β-keto or α,β-ester group will reduce the value of a rate coefficient by a factor of ∼110, ∼2.5 and ∼12 for reaction with NO3, OH or O3, respectively. The actual identity of the alkyl group, R, in −C(O)R or −C(O)OR has only a small influence. An assessment of the reliability of the SAR is given that demonstrates that it is useful for reactions involving NO3 and OH, but less valuable for those of O3 or peroxy nitrate esters.
Keywords: Hydroxyl; Nitrate; Ozone; MP2; Correlation; Atmospheric; Radical;