Atmospheric Environment (v.38, #39)

Comparison of aerosol vertical profiles derived by passive and active remote sensing techniques—a case study by B. Padma Kumari; A.L. Londhe; H.K. Trimbake; D.B. Jadhav (6679-6685).
Simultaneous observations were carried out with twilight photometer and lidar at the National MST Radar Facility (NMRF), Gadanki (13.45°N, 79.18°E) during March 2003, in order to validate the photometer derived profiles, especially the relative heights of the observed dust layers. The aerosol vertical profiles retrieved by both the techniques were compared. The comparison was found to be qualitative. The results showed that the screening height (correction factor to the geometrical Earth's shadow height) for twilight technique was about 6 km for red light, below which no direct information on atmospheric aerosols can be obtained. The results evidenced the presence of high cirrus cloud with base height ranging from 11 to 14 km and stratospheric aerosol layer, or Junge layer (17–23 km), in the profiles derived by both the techniques.
Keywords: Twilight photometer; Lidar; Stratospheric aerosol layer; Cirrus cloud;

The levels of the 2,3,7,8-substituted congeners of polychlorinated dibenzo-p-dioxins (2,3,7,8-PCDDs) and polychlorinated dibenzofurans (2,3,7,8-PCDFs) were measured in ambient air in Houston, TX between September 2002 and April 2003. Samples collected from five locations showed that the monthly total average 2,3,7,8-PCDD/PCDF concentrations ranged from 808 to 1760 fg m−3 with an average of 1235 fg m−3, consistent with their counterparts from other urban areas. From the measured concentrations, it was also observed that: (i) Houston exhibited low 2,3,7,8-TCDD and 2,3,7,8-TCDF concentrations, (ii) the fall and winter V/P ratios for Houston were close to one, probably due to elevated winter temperatures, (iii) the highest chlorinated 2,3,7,8-PCDD/PCDFs exhibited the highest concentrations, and (iv) 2,3,7,8-substituted congeners of PCDDs were the major contributors to the International Toxic Equivalent. The last three observations differ from the literature.Gas–particle partitioning (K oa-based and P L ∘ -based) models were used to describe the distribution of the 2,3,7,8-substituted congeners for Houston. It was determined that P L ∘ estimates using retention indices were more accurate than those obtained with entropy-based approaches. The research demonstrates that PM2.5 and PM10 can be used instead of total suspended particle to estimate K p, although it was shown that PM10 is more appropriate for relating the particulate fraction to K oa. Finally, the research demonstrates that K p− P L ∘ partitioning models are improved by adding relative humidity as a variable to the correlation analysis.
Keywords: Dioxins; Furans; Congeners; Urban ambient air; Vapor/particle partitioning;

Air quality in many of the cities in India is gradually deteriorated due to various activities. One of such activities is open burning of garden biomasses in cities. This study was aimed to estimate the emissions from various types of garden biomasses, namely grass, leaves, twigs and mixtures of these three in a controlled SIFT chamber. Though the particulate emission (1.51 g kg−1) was the lowest from grass, the particle size distribution indicates that the emission contains 10% of fine particulates (<2.5 μm) and significant quantity (70%) of respirable fraction (<10 μm). On the other hand, leaves, though generating 32.3 g kg−1 particulate matter, contained major portion in non-respirable range (around 40%). CO2 emission from leaves (1064.6 g kg−1) and twigs (897.3 g kg−1) are significantly lower than the emission from a mixture (1423 g kg−1) of equal proportion of these two. Similar trend is followed in case of carbon monoxide and nitrogen oxide emissions. However, hydrocarbon emission followed a reverse trend of emitting high emission load (11.4 g kg−1) in the mixture of leaves and twigs than their individual type (2.4 g kg−1 (leaves) and 0.2 g kg−1 (twigs)). The toxicity indices for all categories were very low (0.06–0.12). However, out of the five categories, grass was found to have the lowest toxicity index (0.06) and followed by the mixture (1:1:1), having 0.07. The particulate matter emission load computed for the cities of India shows that the leaves and grass contribute 97 and 4.5 tons day−1, respectively. Among the gaseous pollutants, CO2 emission was the highest, as the computed values were 3212 tons day−1 from leaves and 92 tons day−1 from grass.
Keywords: Garden biomass; Combustion gases; Particulate matter emission;

In order to maintain an acceptable indoor air quality (IAQ), policies, strategies and guidelines on achieving the required IAQ have been developed worldwide. In Hong Kong, the Environmental Protection Department (HKEPD) has launched an IAQ certification scheme to promote an acceptable IAQ in workplaces. For the practical radon measurement, an 8-h continuous monitoring is proposed for the assessment purpose. However, the uncertainties and measurement efforts associated with the method have not been detailed. In this study, the probable errors and measurement efforts in measuring the indoor radon concentration by three proposed sampling schemes of various sampling periods have been investigated. Scheme A is to obtain an average concentration over a sampling period in an occupied period; Scheme B is to obtain an average concentration in two sampling periods from two sessions of the occupied period; and for Scheme C, the average concentration in two structural sampling periods from two sessions of the occupied period. In particular, a 1-year measurement of indoor radon concentration in a typical office building has been used as basis to evaluate the probable errors between the long-term average and those obtained by the three measurement schemes. At a certain confidence level, the results show that the measurement time required for Schemes B and C could be reduced significantly, when compared with Scheme A using continuous monitoring. It is recommended to specify the measurement uncertainty and effort in future codes, and the sampling schemes could be considered in determining the practical strategies for radon measurement.
Keywords: Radon measurement; Sampling period; Confidence level;

Atmospheric gas-phase degradation and global warming potentials of 2-fluoroethanol, 2,2-difluoroethanol, and 2,2,2-trifluoroethanol by Stig Rune Sellevåg; Claus J. Nielsen; Ole Amund Søvde; Gunnar Myhre; Jostein K. Sundet; Frode Stordal; Ivar S.A. Isaksen (6725-6735).
The vapour phase reactions of 2-fluoroethanol, 2,2-difluoroethanol, and 2,2,2-trifluoroethanol with OH radicals and Cl atoms were studied at 298 K and 1013 mbar using long-path FTIR detection. The following reaction rate coefficients were determined by the relative rate method: k 298(OH+CH2FCH2OH)=(1.42±0.11)×10−12, k 298(OH+CHF2CH2OH)=(4.51±0.06)×10−13, k 298(OH+CF3CH2OH)=(1.23±0.06)×10−13, k 298(Cl+CH2FCH2OH)=(2.67±0.3)×10−11, k 298(Cl+CHF2CH2OH)=(3.12±0.06)×10−12, and k 298(Cl+CF3CH2OH)=(7.42±0.12)×10−13  cm3 molecule−1  s−1; the reported uncertainties represent 3 σ from the statistical analyses and do not include any systematic errors or uncertainties in the reference rate coefficients. Quantitative infrared cross-sections of the title compounds at 298 K are reported in the 4000–50 cm−1 region.A 3D chemistry transport model was applied to calculate the atmospheric distributions and lifetimes of the title compounds; the global and yearly averaged lifetimes were calculated as 20 days for CH2FCH2OH, 40 days for CHF2CH2OH, and 117 days for CF3CH2OH. Radiative forcing calculations were carried out assuming either constant vertical profiles or the distribution derived from the chemistry transport model. The Global Warming Potentials for the title compounds are insignificant compared to, e.g. CFC-11 (CCl3F).
Keywords: Infrared absorption cross-sections; Radiative forcings; OH radical; Cl atoms; Atmospheric lifetimes;

Sea-land breezes (SLBs) play an important role in transporting air pollution from urban areas on the coast. In this study, a meso-scale model MM5 was used to simulate SLBs and to understand the transport of pollution during a prolonged ozone episode observed in Hong Kong in September 2001. With the designed settings, the model performed very well in the simulation of SLBs. The simulated surface winds and the planetary boundary layer (PBL) heights are presented to contrast the characteristics of dispersion and transport on pre-episode and episode days. The diurnal variations in horizontal and vertical winds on an episode day are then presented to illustrate the evolution of SLBs. The results indicate that on episode days the onset of sea breezes (SBs) was delayed to noontime due to offshore synoptic winds, while on pre-episode days the SBs had already penetrated deep inland by early afternoon. The simulation shows that SBs propagated in both onshore and offshore directions in the afternoon, leading to the formation of nocturnal regional-scale SBs. The maximum distance for the inland penetration of an SB front (SBF) was about 60–80 km, in contrast to 120–150 km for offshore propagation. With the aid of high-resolution trajectories, the main meteorological factors contributing to the occurrence of the observed ozone episode are discussed. It is believed that the offshore synoptic wind, the delayed SBs, as well as the low mixing height contributed to the daytime transport of pollution and high ozone on the coast. The trajectory analysis also indicates important contributions from regional sources of emission.
Keywords: MM5; Sea-breeze front; Typhoon; Ozone episode; Back-trajectory;

Theoretical model of the Bergeron–Findeisen mechanism of ice crystal growth in clouds by N.E. Castellano; E.E. Avila; C.P.R. Saunders (6751-6761).
A numerical study of growth rate of ice particles in an array of water droplets (Bergeron–Findeisen mechanism) has used the method of electrostatic image charges to determine the vapour field in which a particle grows. Analysis of growth rate in various conditions of relevance to clouds has shown that it is proportional to liquid water content and to ice particle size, while it is inversely proportional to cloud droplet size. The results show that growth rate is enhanced by several percent relative to the usual treatment in which vapour is assumed to diffuse from infinity towards a growing ice particle. The study was performed for ice particles between 25 and 150 μm radii, water droplet sizes between 6 and 20 μm diameter and a wide range of liquid water contents. A study was also made to determine the effect of reducing the vapour source at infinity so that the droplets alone provided the vapour for particle growth. A parameterisation of ice particle growth rate is given as a function of liquid water content and ice particle and droplet sizes. These studies are of importance to considerations in thunderstorm electrification processes, where the mechanism of charge transfer between ice particles and graupel could take place.
Keywords: Vapour diffusion; Ice particle growth; Mixed-phase cloud; Bergeron–Findeisen process; Image charges;

Redox transformations of mercury in an Arctic snowpack at springtime by Alexandre J. Poulain; Janick D. Lalonde; Marc Amyot; Justin A. Shead; Farhad Raofie; Parisa A. Ariya (6763-6774).
We investigated the springtime temporal dynamics of both total mercury (Hg) and gaseous Hg in snowpacks from the High Arctic. In situ incubation experiments of snow samples indicated that the production of volatile mercury in snow (VMS) was photo-mediated and occurred in the first 3 cm of snow. The newly produced VMS (consisting mainly of elemental Hg) was partly oxidized back to Hg(II) when light intensity declined or in the absence of UV radiation, probably through a chain of reactions involving photo-induced radicals and organic compounds in the surface snow. During a 2 week monitoring of total Hg in surface snow, we observed a sharp increase in total Hg concentrations, reaching levels 11 times higher than background concentrations, likely as a result of an atmospheric mercury depletion event. Stratigraphic depth profiles indicated that this increase was restricted to the first 2 cm of the snowpack. Total Hg levels subsequently decreased by 92%, reaching background concentrations within 2 days after this event. The photoproduction rate of VMS calculated on the basis of this episode could account for subsequent daily loss of total Hg from the surface of the snowpack.
Keywords: Arctic; Oxidation; Reduction; Mercury; Snow;

Assimilative capacity and dispersion of pollutants due to industrial sources in Visakhapatnam bowl area by T.V.B.P.S. Rama Krishna; M.K. Reddy; R.C. Reddy; R.N. Singh (6775-6787).
The assimilative capacity and the dispersion of pollutants due to industrial sources have been studied in the Visakhapatnam bowl area situated in coastal Andhra Pradesh, India. Visakhapatnam hosts several major industries. These industries contribute significantly to the air pollution in this coastal city. The assimilative capacity of the Visakhapatnam bowl area's atmosphere has been studied using two different approaches in two seasons, namely, summer and winter of 2002–2003. The first approach is based on ventilation coefficient, which is determined through micro-meteorological data, and the second approach is based on pollution potential in terms of concentration of pollutants determined using air pollution dispersion models. The concentrations of two gaseous pollutants sulphur dioxide and oxides of nitrogen have been computed using two models, namely, Gaussian Plume Model (GPM) and Industrial Source Complex Short Term (ISCST-3) model in the Visakhapatnam bowl area in the summer and winter seasons, respectively. The concentrations of the gaseous pollutants have been measured as 8-h averages at 10 monitoring stations in summer season and at 12 monitoring stations in winter season. The computed 8-h averaged concentrations have been compared with those monitored concentrations at different receptors in both the seasons. The validation of the models has been carried out through quantile–quantile (Q–Q) plots and by computing several statistical errors. The results indicate that both models’ predictions have shown a similar trend with those observed concentrations in the study area. The GPM shows a slight overprediction whereas the ISCST-3 model shows an underprediction in comparison with the observed concentrations.
Keywords: Ventilation coefficient; Mixing height; Elevated sources; Observed concentrations; Bowl area; Statistical errors;

In October 1994, the tracer gas perfluoro-methyl-cyclohexane (PMCH) was released over a 12-h period from a location in northwestern France and tracked at 168 sampling locations in 17 countries across Europe. This release, known as the European Tracer Experiment (ETEX), resulted in the collection of a wealth of data. The authors have obtained 46 sets of transport and dispersion predictions associated with models from 17 countries from the Joint Research Centre of the European Commission as well as the PMCH sampling data. This paper compares predictions and observations, paired in space and time, via the application of a previously developed user-oriented measure of effectiveness (MOE). First, model predictions of ETEX are compared using the MOE and “ranked” by a variety of notional user criteria. The development of these criteria are described. Next, the sensitivity of MOE estimates to any single sampler location is analyzed and the use of the MOE to explore the time-dependence of model performance is described. Finally, the model prediction rankings described in this work are briefly compared with previous related research.
Keywords: Model intercomparison; Transport and dispersion; Measure of effectiveness; European tracer experiment (ETEX);

Karak Industrial Estate (KIE) was investigated for its heavy metals content. Samples of dust, street dust and soil were analyzed for their content of Fe, Cu, Zn, Ni and Pb after digestion with nitric acid. The results of the analysis were used to determine major sources and magnitude of heavy metals pollution. The ranges of heavy metal concentrations in the investigated area were 58.8–94.8, 1.8–84.9, 15.4–136.9, 1.7–6.5 and 2.1–314.1 mg kg−1  dry soil for Fe, Cu, Zn, Ni and Pb, respectively. The concentrations of heavy metals in soils are greater on the surface but decreased in the lower part as a result of the basic nature of this soil. There are two possible sources of heavy metals (Zn, Cu, Ni and Pb) anthropogenic and industrial activities from the work place in KIE. Significant contribution from industrial sources at KIE was evident at nearby places.
Keywords: Heavy metal; Street dust; Dust; Work place; Karak; Jordan;

As a part of the Big Bend Regional Aerosol and Visibility Observational Study (BRAVO, July–October 1999), aerosol physical, optical and chemical properties were measured continuously in an effort to characterize visibility in Big Bend National Park. Surface-based estimates of aerosol extinction coefficients derived from size distribution data were compared to aerosol optical properties retrieved independently from ground-based remote sensing measurements from the United States Department of Agriculture (USDA) UVB radiometer network site. Comparisons suggested that for the majority of the study, surface visibility was a good indicator of the column aerosol optical depth, with a correlation coefficient of r 2 = 0.77 . The average (and one standard deviation) aerosol optical depth from the USDA network was 0.13±0.06 at a wavelength of 500 nm. Ångstrom wavelength exponents were computed for both data sets to characterize the spectral variations of aerosol optical properties over the wavelength range of 415–860 nm. Variations in Ångstrom exponents corresponded to changing aerosol properties as seen in the ground-based composition and size distribution data sets. The average Ångstrom exponent from in situ measurements was 1.5±0.4 compared to column estimates of 1.3±0.4. The root mean square of the difference between the estimates of Ångstrom exponents was 0.20 (∼12%) and on average the estimates were highly correlated ( r 2 = 0.89 ). Aerosol optical depths and ambient surface aerosol extinction coefficients were positively correlated with PM2.5 sulfate mass concentrations ( r 2 = 0.68 and r 2 = 0.79 , respectively), suggesting that sulfate aerosols were a major contributor to visibility degradation and column aerosol loading during the study.
Keywords: Ångstrom exponent; Dust; Sulfate aerosols; Extinction coefficient; Aerosol optical depth; Aerosol optical properties; Visibility; Remote sensing; Sun photometer;

Application of selective non-catalytic reduction of NO x in small-scale combustion systems by Khandoker Abul Hossain; Mohammad Nazri Mohd Jaafar; Azeman Mustafa; Kiran Babu Appalanidu; Farid Nasir Ani (6823-6828).
The selective non-catalytic reduction of NO x has been studied experimentally employing commercial grade urea in a pilot-scale diesel-fired tunnel furnace at 3–4% excess oxygen level and with low ppm of baseline NO x ranging from 65 to 75 ppm within the investigated temperature range. The furnace simulated the thermal behavior of small-scale combustion systems such as small capacity boilers, water heaters, oil heaters, etc., where the operating temperatures remain within the range of 950–1300 K. NO x reductions were studied with the variation of injection temperature, residence time, normalized stoichiometric ratio (NSR) of the reagent, etc. With 5% urea solution, at an NSR of 4, as much as 54% reduction was achieved at 1128 K. The result is quite significant, especially for the investigated level of baseline NO x . The ammonia slip measurements showed that the slip was below 16 ppm at NSR of 4 and optimum temperature of NO x reduction. Finally, the investigations have demonstrated that selective non-catalytic reduction process is quite applicable to the small-scale combustion applications.
Keywords: NSR; Ppm; Temperature window; Ammonia; Slip;

Source apportionment of ambient VOCS in Mumbai city by Anjali Srivastava (6829-6843).
Air pollution kills almost half a million Asians every year. Most of this pollution is emitted from buses, trucks, motorcycles and other forms of transport. As Asia's cities continue to expand, the rising number of vehicles has resulted in even greater pollution. Amongst the measures available to control, vehicular emission was engine modification, catalytic converters and fuel modifications. Some of these have led to emissions of some hazardous air pollutants (HAP) like volatile organic compounds (VOCs). VOC emission is an area needing attention in air quality management. This paper discusses a study on VOC concentration at major sources like traffic junction, residential area, commercial areas, industrial areas and petrol pumps in Mumbai city.CMB8 Model has been used to apportion VOCs in Mumbai city. It was observed that evaporative emissions dominate in Mumbai. In order to control VOCs in air the management strategy should thus focus on cost effective vapor recovery systems at refueling stations and in vehicles. Effective inspection and maintenance programme can reduce evaporative and exhaust VOC emissions. Modifying certain fuel parameters, like reducing benzene content in petrol will as well reduce VOC content in air. The benzene content in petrol was 3% in the year 2001 in Mumbai. Adulteration also results in high levels of VOCs in air.
Keywords: CMB; VOC; Mumbai city; Source apportionment;

Graphical techniques for interpreting the composition of individual aerosol particles by Hui Yuan; Kenneth A. Rahn; Guoshun Zhuang (6845-6854).
A graphical technique that uses XY and ternary plots is presented for interpreting elemental data for individual aerosol particles. By revealing the multiple functional relationships between the elements, it offers more insight into the groups of particles and the transitions between them than traditional techniques such as factor analysis and cluster analysis alone are able to. For a sample of dust storm aerosol from Beijing in March 2002, X–Y plots revealed areas, lines, and “dots” that represented clays, smooth transitions to asymptotes of pure single-component minerals, and pure minor minerals or special particles, respectively. Ternary plots further revealed ratios of elements and potential minerals. Careful use of cluster analysis revealed subgroups of particles that were not separated by clear borders. The dust storm had three major components, clay/quartz (Al2O3, SiO2, etc.), basic calcium (CaO, CaCO3), and salts (sulfate, phosphate, chloride). Some sulfates, including CaSO 4 and (NH4) x H2− x SO 4 , were mixed with the quartz and clay. A five-step sequence that combines graphics, basic statistics, cluster analysis, and SEM photography seems to extract the maximum information from suites of single particles.
Keywords: Graphic analysis; Individual particles; Aerosol; SEM-EDX; Dust storm;

Evaluation of a micrometeorological mass balance method employing an open-path laser for measuring methane emissions by R.L. Desjardins; O.T. Denmead; L. Harper; M. McBain; D. Massé; S. Kaharabata (6855-6866).
In trials of a mass balance method for measuring methane (CH4) emissions, sonic anemometers and an open-path laser were used to measure the transport of CH4 released from a ground-level source across a downwind face 50 m long and 6 m high. Release rates matched emissions expected from dairy herds of 2 to 40 cows. The long laser path permitted inferences from measurements in only two planes, one upwind and one downwind, while the fast-response instruments allowed calculation of instantaneous horizontal fluxes rather than fluxes calculated from mean wind speeds and mean concentrations. The detection limit of the lasers was 0.02 ppmv, with the separation between the transmitters and reflectors being about 50 m. The main conclusions from the 23 trials were: (1) Emissions calculated from mean wind speeds and concentrations overestimated the true emissions calculated from instantaneous measurements by 5%. (2) Because of small changes in methane concentration, the minimum sample size in animal trials would be 10 dairy cows, producing about 40 mg CH4  s−1. (3) For release rates greater than 40 mg CH4  s−1 and with sufficient replication, the technique could detect a change in production rate of 9% ( P < = 0.05 ). (4) Attention to perceived weaknesses in the present technique should help towards detecting changes of 5%.
Keywords: Anthropogenic methane emissions; Mean horizontal flux; Recovery rates; Open-path laser-based gas analyzers; Mass balance method;

Phosphine (PH3), was recently found worldwide even in the remote atmosphere (Naturwissenschaften83(1996a)131; Atmos. Environ. 37(2003)24 29). It is of interest to find natural mechanisms which could produce phosphine gas and drive a volatile link of the atmospheric phosphorus cycle and the formation of phosphoric acid as possible condensation nuclei for clouds.Here, we report on simulated lightning exposing sodium phosphate in a reducing medium (methane model atmosphere or organic matter) for 5 s to a spark induced by microwave. The gas product analyzed by gas chromatography contained phosphine (yield up to 0.6 g kg−1 phosphate P) and methylphosphine (CH3)PH2 (yield up to 0.02 g kg−1 phosphate P).We suggest a plasma-chemical formation mechanism where organic compounds or methane or secondary hydrogen thereof reduce phosphate to phosphine of which a small fraction can subsequently react with methyl radicals to form methylphosphine. A small yield of 6 mg phosphine per kg phosphate P was even obtained in methane free medium, by simple plasmatic recombination of inorganic phosphorus. We believe that methane and hydrogen are useful model substances of pyrolytic gases with high reducing power which may form if lightning strikes biomass, soil and aerosol.These results suggest evidence that phosphine and methylphosphine (detectable in the field by intense garlic odor) are produced when atmospheric lightning strikes the ground or aerosol which is containing oxidized forms of phosphorus and chemical reductants.Additional reviewed data show that laboratory lightning was able to reduce a much more significant portion of phosphate to phosphite (up to 25% yield), methylphosphonic acid (up to 8.5% yield) and traces of hypophosphite in a matter of seconds.
Keywords: Phosphonic acid; Phosphinic acid; Methylphosphonic acid; Odor; Condensation nuclei;

Precipitation samples were collected from July 2001 through June 2002 to determine sources of anthropogenic heavy metal pollutants to Kejimkujik National Park, Nova Scotia using Pb isotope ratios. Generally, Mean annual Pb concentrations (0.116 μg l−1) and depositional fluxes (151 μg m−2) are lower than other reported mid-Atlantic coastal regions. Pb isotope compositions may be explained by binary mixing of anthropogenic emissions from US and Canadian sources, indicating long-range atmospheric transport of pollutants from populated and industrial regions of northeastern US and southeastern Canada. The 206Pb/207Pb ratios in precipitation ranged from 1.165 to 1.201, with an annual weighted mean 206Pb/207Pb ratio of 1.181, indicating that on an annual basis, US and Canadian sources contribute 61% and 39%, respectively, of the anthropogenic Pb (and likely other similarly behaved metal pollutants) reaching Kejimkujik Park. These results differ from those estimated by using epiphytic lichens due to one or a combination of the following possibilities: (1) some of the Pb in the lichens reflects more radiogenic local bedrock sources; (2) there has been an overall increase in the proportion of Canadian inputs since the early 1990s; (3) there was an unusually higher proportion of Pb inputs from Canadian sources during the study period; or (4) possible shifts in the isotopic composition of the Canadian and US sources that may have occurred due to increased international trade in lead and a lesser dependency on national production. As well, seasonal variations in the sources were observed, with summer and fall months having a lower mean 206Pb/207Pb ratio of 1.178 (more Canadian) than the winter and spring months with 206Pb/207Pb of 1.185 (more American).
Keywords: Lead; Lead isotopes; Wet deposition; Air pollution; Atlantic coast; Seasonal variation.;

This study extends a large eddy simulation model used to simulate turbulent flow in an urban street canyon to the dispersion and transport of reactive pollutants (NO, NO2 and O3). The original model, based on the regional atmospheric modelling system, has previously been validated against wind tunnel experiments for wind flow and turbulence. A real scale street canyon with an aspect ratio of one was studied with a neutrally stratified atmosphere and initial wind perpendicular to the street axis. After initialising and running the model to generate a stationary turbulent flow a constant discharge source of NO x was specified to imitate steady traffic flow through the street canyon. Line and area emissions sources for low and medium emissions of NO x were considered. A background concentration of ozone was specified and the gases were allowed to mix and react. Spatial variation of pollutants within the canyon was calculated to be significant. The photostationary state defect, ( δ ps = k [ NO ] [ O 3 ] / J NO 2 [ NO 2 ] - 1 ) , was found to be a sensitive indicator of reactive mixing within the canyon, the greater the defect the greater the local state of chemical instability. Low values for δ ps were found at the centre of the street canyon, within the primary vortex, and at the ground level corner of the windward wall, where a secondary eddy was predicted. High values were found above ground level along the windward wall, where air was entrained into the canyon along the outer edge of the primary vortex, and downstream of, and close to the NO x emission. Above the canyon a region of high δ ps corresponds to the edge of the escaping canyon plume.
Keywords: Large-eddy simulation; Street canyon modelling; Traffic emissions; Ozone; Photostationary state defect;

PM2.5 and PM2.5–10 samples were collected between August 1998 and March 1999 at Taichung urban and coastal sites. The major objective in this study was to identify the source contributions to PM10 in different air quality conditions. Principal component analysis with varimax rotation and a chemical mass balance model were used to qualify and quantify, respectively, the source contributions to PM10. Vehicle emissions was the most important source of PM10 at the urban site, followed by crustal materials, secondary aerosols, biomass burning, industrial emissions and marine spray. There was a similar pattern of sources at the coastal site, except that marine spray was found more significantly than the urban site. Although biomass burning and secondary aerosols were not main sources during clean air quality periods, they were the influential sources causing the increase of PM10 to “episodic” levels at both sites.
Keywords: Aerosol compositions; Urban; Coastal; Principal component analysis; CMB source apportionment;

Membrane inlet mass spectrometry was used to monitor dissolved gas concentrations and gas exchange rates of CO2, CH4 and O2 in peat cores from three very different locations in the Northern Hemisphere: Kopparås Mire (Sweden), Hestur Site (Iceland), and Ellergower Moss (Scotland). With an increase of temperature gas solubilities are reduced, and due to additionally increased microbial activities higher gas emission rates for both CO2 and CH4 were observed. Experimental alterations of temperature and photosynthetically active radiation (PAR) also drastically effect daytime carbon dioxide emission rates as a result of changes in microbial and plant physiology. The impact of ebullition on gas emission rates was indicated by continuous measurements of gas concentrations in the headspace of Icelandic and Swedish cores using two different experimental setups. For methane, up to 2 3 of the total emission from cores from both sites is released by ebullition. Total gas emission rate measurements in this study were similar for both experimental setups, and revealed gas effluxes comparable with field measurements for Scottish and Icelandic peat.
Keywords: Methanogenesis; Methane oxidation; Membrane inlet mass spectrometry; Peat;