Atmospheric Environment (v.35, #32)

Sources and chemical composition of atmospheric fine and coarse particles in the Helsinki area by Tuomo A Pakkanen; Kati Loukkola; Christina H Korhonen; Minna Aurela; Timo Mäkelä; Risto E Hillamo; Päivi Aarnio; Tarja Koskentalo; Anu Kousa; Willy Maenhaut (5381-5391).
During April 1996–June 1997 size-segregated atmospheric aerosol particles were collected at an urban and a rural site in the Helsinki area by utilising virtual impactors (VI) and Berner low-pressure impactors (BLPI). In addition, VI samples were collected at a semi-urban site during October 1996–May 1997. The average PM2.3 (fine particle) concentrations at the urban and rural sites were 11.8 and 8.4 μg/m3, and the PM2.3−15 (coarse particle) concentrations were 12.8 and about 5 μg/m3, respectively. The difference in fine particle mass concentrations suggests that on average, more than one third of the fine mass at the urban site is of local origin. Evaporation of fine particle nitrate from the VI Teflon filters during sampling varied similarly at the three sites, the average evaporation being about 50–60%.The average fine particle concentrations of the chemical components (25 elements and 13 ions) appeared to be fairly similar at the three sites for most components, which suggests that despite the long-range transport, the local emissions of these components were relatively evenly distributed in the Helsinki area. Exceptions were the average fine particles Ba, Fe, Sb and V concentrations that were clearly highest at the urban site pointing to traffic (Ba, Fe, Sb) and to combustion of heavy fuel oil (V) as the likely local sources. The average coarse particle concentrations for most components were highest at the urban site and lowest at the rural site.Average chemical composition of fine particles was fairly similar at the urban and rural sites: non-analysed fraction (mainly carbonaceous material and water) 43% and 37%, sulphate 21% and 25%, crustal matter 12% and 13%, nitrate 12% and 11%, ammonium 9% and 10% and sea-salt 2.5% and 3.2%, respectively. At the semi-urban site also, the average fine particle composition was similar. At the urban site, the year round average composition of coarse particles was dominated by crustal matter (59%) and the non-analysed components (28%, mainly carbonaceous material and water), while the other contributions were much lower: sea-salt 7%, nitrate 4% and sulphate 2%. At the rural site, the coarse samples were collected in spring and summer and the percentage was clearly lower for crustal matter (37%) and sea-salt (3%) but higher for the not-analysed fraction (51%). At the semi-urban site, the average composition of coarse particles was nearly identical to that at the urban site.Correlations between the chemical components were calculated separately for fine and coarse particles. In urban fine particles sulphate, ammonium, Tl, oxalate and PM2.3 mass correlated with each other and originated mainly from long-range transport. The sea-salt ions Na+, Cl and Mg2+ formed another group and still another group was formed by the organic anions oxalate, malonate, succinate, glutarate and methane sulphonate. Ni and V correlated strongly pointing to combustion of heavy fuel oil as the likely source. In addition, some groups with lower correlations were detected. At the rural and semi-urban sites, the correlating components were rather similar to those at the urban site, although differences were also observed.
Keywords: Atmosphere; Urban; Rural; Fine particles; Coarse particles; Elements; Ions; Chemical composition; Sources;

Volatile organic compounds (VOCs) emitted from 40 Mediterranean plant species: by Susan Margaret Owen; Christophe Boissard; C.Nicholas Hewitt (5393-5409).
Forty native Mediterranean plant species were screened for emissions of the C5 and C10 hydrocarbons, isoprene and monoterpenes, in five different habitats. A total of 32 compounds were observed in the emissions from these plants. The number of compounds emitted by different plant species varied from 19 (Quercus ilex) to a single compound emission, usually of isoprene. Emission rates were normalised to generate emission factors for each plant species for each sampling event at standard conditions of temperature and light intensity. Plant species were categorised according to their main emitted compound, the major groups being isoprene, α-pinene, linalool, and limonene emitters. Estimates of habitat fluxes for each emitted compound were derived from the contributing plant species’ emission factors, biomass and ground cover. Emissions of individual compounds ranged from 0.002 to 505 g ha−1  h−1 (camphene from garrigue in Spain in autumn and isoprene from riverside habitats in Spain in late spring; respectively). Emissions of isoprene ranged from 0.3 to 505 g ha−1  h−1 (macchia in Italy in late spring and autumn; and riverside in Spain in late spring; respectively) and α-pinene emissions ranged from 0.51 to 52.92 g ha−1  h−1 (garrigue in Spain in late spring; and forest in France in autumn; respectively). Habitat fluxes of most compounds in autumn were greater than in late spring, dominated by emissions from Quercus ilex, Genista scorpius and Quercus pubescens. This study contributes to regional emission inventories and will be of use to tropospheric chemical modellers.
Keywords: Monoterpene emissions; Isoprene emissions; Branch enclosure; Volatile organic compounds flux; Mediterranean vegetation; Extrapolation to regional scale; Biogenic VOC speciation;

An explicit multiphase chemistry model (Atm. Environ. 34 (29/30) (2000) 5015) has been coupled with quasi-spectral microphysics, based upon Berry and Reinhardt's parameterizations (1974a, b). This coupled model has been initialized with polluted conditions as observed at the Puy de Dôme mountain in the center of France and for a maritime cloud.The presence of clouds results in two effects on multiphase chemistry: a direct effect through mass transfer, solubility and reactivity, and an indirect effect through microphysical transfer from cloud water into rainwater and redistribution of reactive soluble species among interstitial air, cloud droplets and raindrops.Results demonstrate that microphysical processes are necessary to sketch out the complex, nonlinear multiphase chemistry in a real cloud. In addition to the direct exchange through mass transfer, incorporation of reactive oxidants such as HO x in droplets can arise and consequently make those species no longer available for reacting in the gas-phase. Moreover, microphysical coalescence conversions favor NO x destruction and enhance the chemical nitric acid production. Coalescence of cloud drops to form rain transfers dissolved species into drops that are undersaturated compared to Henry's law equilibrium. The rain becomes a reservoir for these species, allowing aqueous chemistry to produce more nitric acid than would be possible without the presence of rain.Finally, for the different cloud types, the fate of those intermediate and reactive species is investigated, looking at their budget in clear sky situation versus cloudy and/or rainy situations.
Keywords: Cloud multiphase chemistry; Numerical modeling; Microphysics; Rain formation;

The uncertainty associated with the Austrian Greenhouse Gas emission inventory has been determined for the gases CO2, CH4 and N2O and for the overall greenhouse potential. Expert interviews were conducted to obtain uncertainties in inventory input data. Based on these interviews, error distributions were developed and combined using Monte-Carlo analysis. Results for all sources and gases combined indicate an overall uncertainty between 10.5% and 12% depending on the base year considered. Excluding emissions and the uncertainty associated with forest sinks and natural sources, overall uncertainty decreased by 2% points. The mere ‘random error’, which is considered the level of uncertainty to be achieved with the current methodology (excluding all systematic errors) is 5% points lower. Detailed evaluation shows that much of the overall uncertainty derives from a lack of understanding the processes associated with N2O emissions from soils. Other important contributors to GHG emission uncertainties are CH4 from landfills and forests as CO2 sinks. The uncertainty of the trend has been determined at near 5% points, with solid waste production (landfills) having the strongest contribution. Theoretical considerations do not permit a decrease of the trend uncertainty—even when forest sinks are not considered—below 3% points.
Keywords: Uncertainty; Emissions; Greenhouse gases; Monte-Carlo simulation;

The typical features of a summer smog episode in the highly complex terrain of the Province of Bolzano (Northern Italy) were investigated by numerical modelling with two non-hydrostatic models, ground-based monitoring stations, and vertical profiling with two sodars and an ultra-light aircraft. High ozone concentrations are most likely to appear in situations where the local circulation in the valleys is decoupled from the synoptic flow above during anticyclonic weather regimes. Both models (MM5 and TVM) produced similar results and were able to simulate the local winds in the valleys. A comparison of the measured data to the model simulation results made an evaluation of the performance of the two models in such complex terrain possible. Both models proved to be suitable for the simulation of the meteorological conditions during such summer smog episodes in complex terrain.
Keywords: Numerical modelling non-hydrostatic; Complex terrain; Vertical profiling with sodar and aircraft; Mountain meteorology; Air quality in valleys;

Modelling atmospheric mercury transport and deposition across Europe and the UK by D.S. Lee; E. Nemitz; D. Fowler; R.D. Kingdon (5455-5466).
There are inadequate measurements of surface ambient concentrations of mercury species and their deposition rates for the UK deposition budget to be characterized. In order to estimate the overall mercury flux budget for the UK, a simple long-term 1D Lagrangian trajectory model was constructed that treats emissions (1998), atmospheric transformation and deposition across Europe. The model was used to simulate surface concentrations of mercury and deposition across Europe at a resolution of 50 km×50 km and across the UK at 20 km×20 km. The model appeared to perform adequately when compared with the few available measurements, reproducing mean concentrations of elemental gaseous mercury at particular locations and the magnitude of regional gradients. The model showed that 68% of the UK's mercury emissions are exported and 32% deposited within the UK. Of deposition to the UK, 25% originates from the Northern Hemisphere/global background, 41% from UK sources and 33% from other European countries. The total mercury deposition to the UK is in good agreement with other modelling, 9.9 tonne yr−1 cf. 9.0 tonne yr−1, for 1998. However, the attribution differs greatly from the results of other coarser-scale modelling, which allocates 55% of the deposition to the UK from UK sources, 4% from other European countries and 60% from the global background atmosphere. The model was found to be sensitive to the speciation of emissions and the dry deposition velocity of elemental gaseous mercury. The uncertainties and deficiencies are discussed in terms of model parameterization and input data, and measurement data with which models can be validated. There is an urgent requirement for measurements of removal terms, concentrations, and deposition with which models can be parameterized and validated.
Keywords: Mercury; Modelling; Atmospheric budgets; Long-range transport;

Determination of PAN, PPN, PnBN and selected pentyl nitrates in Athens, Greece by Sotirios Glavas; Nektarios Moschonas (5467-5475).
Quasi-continuous measurements of PAN, PPN, PnBN and the alkyl nitrates—2-methyl-2-butyl nitrate, 3-pentyl nitrate and 2-pentyl nitrate were carried out in Athens using a simple cryoconcentration technique. The maximum mixing ratios measured were 6.6, 1.0 and 0.07 ppbv for PAN, PPN and PnBN, respectively, for the peroxyacyl nitrates, and 0.3, 0.09 and 0.03 ppb for 2-methyl-2-butyl nitrate, 2-pentyl nitrate and 3-pentyl nitrate, respectively. Mean ratios of PPN/PAN mixing ratios were 0.102 and of PnBN/PAN 0.012. 2PN/3PN mean ratios were 1.8 near the theoretical value of 1.6. All maximum values of measured nitrogenous compounds were associated with maximum mixing ratios of ozone and NO x and occurred when southwestern winds prevailed in association with a temperature inversion.
Keywords: Peroxyacetyl nitrate (PAN); Peroxypropionyl nitrate (PPN); Peroxy-n-butyrylnitrate (PnBN); 2-methyl-2-butyl nitrate (2M2BN); 3-pentyl nitrate (3PN); 2-pentyl nitrate (2PN); Ozone; Urban;

Estimates of air-sea exchange of mercury in the Baltic Sea by Ingvar Wängberg; Stefan Schmolke; Peter Schager; John Munthe; Ralf Ebinghaus; Åke Iverfeldt (5477-5484).
The concentrations of total gaseous mercury (TGM) in air over the southern Baltic Sea and dissolved gaseous mercury (DGM) in the surface seawater were measured during summer and winter. The summer expedition was performed on 02–15 July 1997, and the winter expedition on 02–15 March 1998. Average TGM and DGM values obtained were 1.70 and 17.6 ng m−3 in the summer and 1.39 and 17.4 ng m−3 in the winter, respectively. Based on the TGM and DGM data, surface water saturation and air-water fluxes were calculated. The results indicate that the seawater was supersaturated with gaseous mercury during both seasons, with the highest values occurring in the summer. Flux estimates were made using the thin film gas-exchange model. The average Hg fluxes obtained for the summer and winter measurements were 38 and 20 ng m−2  d−1, respectively. The annual mercury flux from this area was estimated by a combination of the TGM and DGM data with monthly average water temperatures and wind velocities, resulting in an annual flux of 9.5 μg m−2  yr−1. This flux is of the same order of magnitude as the average wet deposition input of mercury in this area. This indicates that reemissions from the water surface need to be considered when making mass-balance estimates of mercury in the Baltic Sea as well as modelling calculations of long-range transboundary transport of mercury in northern Europe.
Keywords: Gaseous mercury; Dissolved gaseous mercury;

Atmospheric particulate matter (PM10) was collected simultaneously at three sites in the West Coast of Portugal, during an intensive campaign in August 1996. The sites were located in line with the breezes blowing from the sea. The collected aerosol was analysed in relation to black and organic carbon content. The particulate organic matter was extracted with solvents and characterised by gas chromatography and mass spectrometry (GC–MS). Most of the organic mass identified consists of alkanes, polycyclic aromatic hydrocarbons (PAH), ketones, aldehydes, alcohols and fatty acids with both biogenic and anthropogenic origin. Many photochemical products from volatile organic compounds emitted by vegetation were also detected. Biomarkers such as 6,10,14-trimethylpentadecanone, abieta-8,11,13-trien-7-one and Patchouli alcohol were observed at higher concentrations in the rural sites. Samples from the urban site present lower values of “carbon preference index” and higher concentrations of petrogenic/pyrogenic species, such as PAH. The PM10 concentrations and the total organic extract measured for the more interior site were generally lower, indicating that dispersion and dry deposition into the forest canopy were more important during the transport of the air masses than aerosol production by condensation and photochemical reactions. On the contrary, the ratio between organic and black carbon was, in general, lower at sites near the coast, especially for compounds that evaporate at lower temperatures. The organic aerosol composition also seems to be strongly dependent on the meteorology.

Keywords: Source-receptor relationship; Online-coupling; Lagrangian particle model; LaMM5; FluMOB;

Keywords: LaMM5; Source-receptor relationship; Euler–lagrange model system; Vertical mixing; FluMOB air monitor experiment;

Emission of heavy metals, besides ozone and diesel-soot, is one of the most significant environmental problems caused by the existing transport systems. Emission arises from different parts of vehicles (tyres, brakes, exhausts) or running trains (rails, wheels, overhead cables, etc.). Various types of emission with their insufficiently known ways of spreading makes it difficult to estimate the risk and to realise effective counter-measures.Size-dependent sampling of aerosols with the virtual impactor technique of a dichotomous sampler (<2.5 μm, 2.5–10 μm) allows one to identify several aerosol components at the sampling locations and to reliably determine their relative proportions. Analyses of 30–40 elements from immission samplings at 12 places in and around Cologne are compared with specific patterns of elements from relevant emission sources. Moreover, taking into account the particle size, relative abundances of Zn, Mo, Cu and Sb can be estimated by assuming an average of around 30% of diesel-soot in the fine fraction, and ∼3% from an abraded tyre material together with ∼0.3% from rubbed off brake-linings in the coarse fraction. The assumption of 0.3% for brake-linings is based on the relative abundances of Cu and Sb which besides Cd are the most highly enriched. Since most brake-linings used in cars contain these elements in an unusually high quantity (5–20% Cu and 1–5% Sb) and are in very similar ratios as measured in the coarse fraction, Cu and Sb may be taken as quantitative tracers for the brake-lining component in the immission. The environmental interest in Sb arises mainly from the toxicological potential of the compounds Sb2S3 and Sb2O3.Other traffic related components could only be identified very close to the sources of emissions. Besides Pt from cars with catalysators and Cu emitted from overhead cables of trams, an As-enrichment from rusting rails, which segregates into fine particles because of shaking due to passing trains, was discovered.
Keywords: Particle emission; Suspended particles; Dichotomous sampling; Neutron activation analysis; Brake-linings; Antimony;

Use of atmospheric elemental size distributions in estimating aerosol sources in the Helsinki area by Tuomo A Pakkanen; Veli-Matti Kerminen; Christina H Korhonen; Risto E Hillamo; Päivi Aarnio; Tarja Koskentalo; Willy Maenhaut (5537-5551).
In June 1996–June 1997 Berner impactors were used in the Helsinki area to measure size distributions of atmospheric aerosols simultaneously at an urban and at a rural site. Ten sample pairs were collected in the size range of 0.03–15.7 μm of equivalent aerodynamic diameter (EAD). Average size distributions at the two sites were calculated for 29 elements, particulate mass, and sulphate. At both sites especially sulphate, As, B, Bi, Cd, Ni, Tl, and V were enriched in fine particles (EAD<2.3 μm). In order to estimate local fine-particle sources of the various chemical components, the similarities and dissimilarities in the accumulation-mode parameters were studied separately for both sites. It was observed that often in different samples, different components had similar accumulation modes. At both sites, particulate mass, As, and Pb had similar accumulation modes to sulphate which suggests that long-range transport (LRT) is important for these components. V, Ni, Mo, and Co formed another group of similar accumulation modes at both sites suggesting that these elements largely originated from local and regional oil combustion. In addition, other groups of similar accumulation modes were observed but these groups were different between the sites. The meteorological parameters indicated that seven sample pairs formed a subset of the data in which the local emissions of the Helsinki area were transported to the urban site but not to the rural site. For this subset the rural fine-particle concentrations were considered to represent an upper limit estimate for the LRT. These upper limit LRT estimations were further improved by utilising the quantitative relative size distributions (QRSD) method at the rural site. The QRSD method supposes that in the fine-particle size range the LRT fractions of all chemical components have a similar shape in their size distributions. Fine-particle sulphate is typically long-range transported, and was therefore selected as the model component that represents the shape of LRT material. Sulphate size distribution was then scaled to give an estimation of the LRT contribution of each component at the rural site. These rural “sulphate scaled” LRT estimates were subtracted from the corresponding urban concentrations to give the local contributions (ng/m3) downwind of the Helsinki area. In particles with EAD below 2.3 μm, the highest absolute and relative downwind local contributions were observed for several common sea-salt and road-dust components. Also the combustion-related elements Ni and V showed fairly high downwind local contributions. Because of the limited number of samples, the local and LRT contributions were not estimated for different wind directions.
Keywords: Atmosphere; Urban; Rural; Elements; Size distribution; Sources; Local; Long-range transport;

Surface ozone at the Swiss Alpine site Arosa: the hemispheric background and the influence of large-scale anthropogenic emissions by Pakpong Pochanart; Hajime Akimoto; Shamil Maksyutov; Johannes Staehelin (5553-5566).
An innovative and effective method using isentropic trajectory analysis based on the residence time of air masses over the polluted region of Europe was successfully applied to categorize surface ozone amounts at Arosa, Switzerland during 1996–1997. The “European representative” background ozone seasonal cycle at Arosa is associated with long-range transport of North Atlantic air masses, and displays the spring maximum–summer minimum with an annual average of 35 ppb. The photochemical ozone production due to the intense large-scale anthropogenic emission over Europe is estimated as high as 20 ppb in summer, whereas it is insignificant in winter. European sources contribute an annual net ozone production of 9–12 ppb at Arosa. Comparison with the selected regional representative site in Western Europe shows similar results indicating that the categorized ozone data at Arosa by this technique could be regarded as a representative for northern hemispheric mid-latitudes.
Keywords: Long-range transport; Regional source; Residence times; Trajectory analysis; Western Europe;

Air pollution in England and Wales is reviewed to identify priorities for management and research. The main human drivers of emissions are the production and consumption of energy and materials, disposal of waste, transport and land use. Pollutants are assigned to seven types: (i) nuisance (e.g. odour, noise), (ii) toxic, (iii) acidifying/eutrophying, (iv) photochemical oxidant precursors, (v) radionuclides, (vi) stratospheric ozone depleting substances and (vii) greenhouse gases. Dominant trends in activity and emissions are highlighted. New technologies and fuels are partially decoupling emissions from activity in power generation, industry and transport, but the gains are being offset by growth in demand and output in all major sectors. The evidence for impacts on human health, the atmosphere and other environmental systems is discussed. Priorities for management are climate change, ground-level ozone, acidification and eutrophication by nitrogen, urban air quality and nuisance pollution. Management responses require greater foresight, technological improvements and new instruments to control polluting activities. More scientific information is needed on the impacts on human health, quality of life and ecosystems, and on the links between different types of pollution. The policy challenges include generating energy sustainably, reducing transport impacts, devising effective economic instruments, improving societal awareness and contributing to cleaner global development.
Keywords: Emissions; Ecosystems; Health; Regulation; Policy;

Long-term changes of ozone and traffic in Bilbao by Gabriel Ibarra-Berastegi; Imanol Madariaga; Ana Elı́as; Elena Agirre; Javier Uria (5581-5592).
It is well known that ozone levels are the result of the interaction among emissions of VOC's and NO x , on the one hand, and meteorological effects on the other hand. In this work, using the low-pass KZ filter developed by Kolmogorov and Zurbenko, the original time series consisting of the logarithm of daily maximum ozone concentrations measured at three locations in the Bilbao area, are splitted into long-term, seasonal and short-term effects. Next, meteorological effects are moderated or removed from filtered ozone series using multiple linear regression. The long-term evolution of ozone forming capability due to changes in precursor emissions can be obtained applying the KZ filter to the residuals of this regression.The present work is an application of the widely used and well known KZ filter technique and focuses on analyzing the joint evolution of the long-term components of ozone time series on the one hand, and mean traffic in the Bilbao area (Spain) on the other hand during years 1993, 1994, 1995 and 1996.To that end, regression analysis between the long-term fractions of ozone and traffic has been performed. The results show that long-term changes of the mean traffic flow are responsible for the long-term changes in ozone forming capability due to changes in precursor emissions of the area. Long-term trend of daily mean traffic can explain between 81% and 99.6% of the total variance of long-term ozone changes at the three locations of Bilbao studied.
Keywords: Kz filter; Kolmogorov–Zurbenko low-pass filter; Long-term trend; Ozone precursor emissions; Traffic; Bilbao;

Variability of indicator values for ozone production sensitivity: a model study in Switzerland and San Joaquin Valley (California) by Sebnem Andreani-Aksoyoglu; Cheng-Hsuan Lu; Johannes Keller; André S.H Prévôt; Julius S Chang (5593-5604).
The threshold values of indicator species and ratios delineating the transition between NO x and VOC sensitivity of ozone formation are assumed to be universal by various investigators. However, our previous studies suggested that threshold values might vary according to the locations and conditions. In this study, threshold values derived from various model simulations at two different locations (the area of Switzerland by UAM Model and San Joaquin Valley of Central California by SAQM Model) are examined using a new approach for defining NO x and VOC sensitive regimes. Possible definitions for the distinction of NO x and VOC sensitive ozone production regimes are given. The dependence of the threshold values for indicators and indicator ratios such as NO y , O3/NO z , HCHO/NO y , and H2O2/HNO3 on the definition of NO x and VOC sensitivity is discussed. Then the variations of threshold values under low emission conditions and in two different days are examined in both areas to check whether the models respond consistently to changes in environmental conditions. In both cases, threshold values are shifted similarly when emissions are reduced. Changes in the wind fields and aging of the photochemical oxidants seem to cause the day-to-day variation of the threshold values. O3/NO z and HCHO/NO y indicators are predicted to be unsatisfactory to separate the NO x and VOC sensitive regimes. Although NO y and H2O2/HNO3 provide a good separation of the two regimes, threshold values are affected by changes in the environmental conditions studied in this work.
Keywords: Ozone; Hydrocarbons; Nitrogen oxides; Photochemical modeling; Indicators;

The project ‘Climate Analysis of the Region of Basel’ (KABA) was carried out in cooperation with several planning authorities to produce climate analysis and planning recommendation maps at scales of 1 : 100,000 and 1 : 25,000. These maps enable urban and regional planners to estimate impacts of land-use changes on local climate and air quality. Conceptual numerical models receiving spatially distributed input data from a geographic information system derived the information content of the maps. By introducing novel concepts concerning land-use and ventilation, the dominant controls for local climate and air quality, automated, knowledge-based classification schemes for climate analysis were developed and applied. The same model technique was utilized for a spatially distributed assignment of planning objectives to the study region. Three different problem sections are considered: ventilation, air quality and thermal situation. Several planning objectives were distinguished within each problem section, and each element of a 100 m grid was individually evaluated by automated, knowledge-based classification procedures. This approach provides a high degree of transparency and objectivity in place of subjective (and thus irreproducible) assessments by experts. Transfer of the procedures to other regions could be successfully demonstrated in a project named ‘Climate Analysis Maps for Planning Aspects of Solothurn/CH (CAMPAS/CH)’ funded by European Space Agency. Hence, the approach is of general interest, at least for many densely populated regions at mid-latitudes.
Keywords: Land-use; Ventilation; Air quality; Thermal situation; GIS;

Mixing properties of individual submicrometer aerosol particles in Vienna by Kikuo Okada; Regina M Hitzenberger (5617-5628).
Individual aerosol particles were collected on 5 days with different meteorological conditions in March, April and June 1991 in the urban atmosphere of Vienna in Austria. The samples collected with an impactor were examined by electron microscopy. The mixing properties of submicrometer aerosol particles with radii between 0.1 and 1 μm were studied by using the dialysis (extraction) of water-soluble material. The averaged results showed that more than 85% of particles with radii between 0.1 and 0.7 μm were hygroscopic. However, more than 50% of particles with radii larger than 0.2 μm were mixed particles (hygroscopic particles with water-insoluble inclusions), and they were dominant (80%) in the size range 0.5–0.7 μm radius. The results also showed that the number proportion of mixed particles increased with increasing radius and the abundance increased with increasing particle loading in the atmosphere. The volume fraction of water-soluble material (ε) in mixed particles tended to decrease with increasing radius, implying the formation of mixed particles by heterogeneous processes such as condensation and/or surface reaction. Some results of elemental composition in individual particles analyzed with an energy-dispersive X-ray (EDX) analyzer equipped with an electron microscope are also presented in this paper.
Keywords: Hygroscopic particles; Single particle analysis; Dialysis technique; Elemental composition; Ionic composition;

Although organic nitrogen (ON) has been found to be a ubiquitous and significant component in wet and dry deposition, almost nothing is known about its concentration or composition in fog waters. To address this gap, we have investigated the concentration and composition of ON in fog waters collected in Davis, in California's Central Valley. Significant quantities of dissolved organic nitrogen (DON) were found in these samples, with a median concentration of 303 μM N (range=120–1630 μM N). DON typically represented approximately 16% of the total dissolved nitrogen (inorganic+organic) in Davis fog waters. The median concentration of nitrogen in free amino acids and alkyl amines was 16 μM N (range=3.8–120 μM N), which accounted for 3.4% of the DON in Davis fogs. Thus, although the absolute concentrations of free amino compounds were significant, they were only a minor component of the DON pool. Combined amino nitrogen (e.g., proteins and peptides) was present at higher concentrations and accounted for 6.1–29% (median=16%) of DON. Overall, free and combined amino compounds typically accounted for a median value of 22% of DON in the fog waters.The high concentrations of DON found, and the fact that amino and other N-containing organic compounds can serve as nitrogen sources for microorganisms and plants, indicate that atmospheric ON compounds likely play an important role in nitrogen cycling in the Central Valley. In addition, due to the basicity of some N functional groups, ON compounds likely contribute to the previously observed acid buffering capacity of Central Valley fog waters. Finally, a comparison of fog waters with fine particles (PM2.5) collected from the same site during the same period of time indicated that the median concentrations (mol N m−3-air) of total water-soluble ON, free amino nitrogen and total amino nitrogen were very similar in the fog water and PM2.5. Given the high water solubility of many organic N compounds, this result suggests that ON might contribute to the hygroscopic properties of atmospheric particles.
Keywords: Fog chemistry; Nitrogen cycling; Amino compounds; PM2.5; Organic carbon;

Ammonia concentrations and fluxes over a forest in the midwestern USA by S.C. Pryor; R.J. Barthelmie; L.L. Sørensen; B. Jensen (5645-5656).
We present measurements of ammonia (NH3) over a deciduous forest in southern Indiana collected during four field campaigns; two in the spring during the transition to leaf-out and two during the winter. Above canopy NH3 concentrations measured continuously using two Wet Effluent Diffusion Denuders indicate mean concentrations of 0.6–1.2 μg m−3 during the spring and 0.3 μg m−3 during the winter. Measurements suggest that on average the forest act as a sink of NH3, with a representative daily deposition flux of 1.8 mg-NH3  m−2 during the spring. However, on some days during the spring inverted concentration gradients of NH3 were observed resulting in an apparent upward flux of nearly 0.2 mg-NH3  m−2  h−1. Analyses suggest that this apparent emission flux may be due to canopy emission but evaporation of ammonium nitrate particles may also be partly responsible for the observed inverted concentration gradients.
Keywords: Ammonia; Forests; Dry deposition; Bi-directional fluxes;

This paper illustrates a simple technique of performing space–time analysis of precipitation-weighted SO4 2− concentration data across the eastern US that were collected by the National atmospheric deposition program. Using a moving average filter and two-dimensional spatial data filtering algorithm on the time series of precipitation-weighted SO4 2− concentrations, we show that decreases of about 50% have occurred in SO4 2− concentrations in Minnesota, Wisconsin, and over the northeastern US between 1985 and 1998, generally consistent with SO2 emissions’ reductions over this period. The decreases in SO4 2− concentrations tended to be smaller in the midwest and south.
Keywords: Sulfates; Acid precipitation; Trend detection; NADP; Space–time analysis;

Polychlorinated biphenyls and particulate organic/elemental carbon in the atmosphere of Chesapeake Bay, USA by Paul A Brunciak; Jordi Dachs; Thomas P Franz; Cari L Gigliotti; Eric D Nelson; Barbara J Turpin; Steven J Eisenreich (5663-5677).
Polychlorinated biphenyls (PCBs) and particulate organic/elemental carbon (OC/EC) differ as to sources, but are both elevated in major urban areas leading to loadings of proximate terrestrial and aquatic systems. Because of the dramatic difference in speciation, sources, and sinks of these compunds, gas+particulate phase PCBs and particulate OC/EC were measured in urban Baltimore, MD and over Chesapeake Bay at 4 and 12 h frequencies in July 1997. Gas phase ∑PCBs averaged 1180 pg m−3 for Baltimore and 550 pg m−3 for northern Chesapeake Bay. PCB homolog distributions in the gas phase differed between the land and over-water sites whereby the trichlorobiphenyls were higher in Baltimore compared to Chesapeake Bay. Autocorrelation analysis yielded a diurnal cycle for gas phase PCBs at Baltimore with the lowest concentrations observed during the day. Particulate organic and elemental carbon constituted 12.4% (17.4% organic matter) and 2.8% of total suspended particles (TSP) in Baltimore, and 15.0% (21.0% organic matter) and 5.3% over the Chesapeake Bay, respectively. Variability in PCB concentrations was not related to the variability in OC/EC concentrations. OC/EC ratios suggest that particulate organic carbon was mostly primary aerosol. Emissions of both classes of compounds into the Baltimore atmosphere and vicinity are major sources to the Bay.

Strategic guidelines for street canyon geometry to achieve sustainable street air quality by Andy T Chan; Ellen S.P So; Subash C Samad (5681-5691).
This paper is concerned with the motion of air within the urban street canyon and is directed towards a deeper understanding of pollutant dispersion with respect to various simple canyon geometries and source positions. Taking into account the present days typical urban configurations, three principal flow regimes “isolated roughness flow”, “skimming flow” and “wake interference flow” (Boundary Layer Climates, 2nd edition, Methuen, London) and their corresponding pollutant dispersion characteristics are studied for various canopies aspect ratios, namely relative height (h 2/h 1), canyon height to width ratio (h/w) and canyon length to height ratio (l/h). A field-size canyon has been analyzed through numerical simulations using the standard k-ε turbulence closure model. It is found that the pollutant transport and diffusion is strongly dependent upon the type of flow regime inside the canyon and exchange between canyon and the above roof air. Some rules of thumbs have been established to get urban canyon geometries for efficient dispersion of pollutants.
Keywords: Pollutant dispersion; Street canyon; Numerical simulation; Three-dimensional model; Critical aspect ratios;