Atmospheric Environment (v.39, #6)

Soiling of silica-soda-lime float glass in urban environment: measurements and modelling by T. Lombardo; A. Ionescu; R.A. Lefèvre; A. Chabas; P. Ausset; H. Cachier (989-997).
Modern silica-soda-lime float glass samples were exposed to background pollution conditions in Paris, sheltered from rain, during 1, 2, 6, 12 and 24 months. Analytical scanning electron microscopy pointed to the importance of soot particles and soluble salts as fine and coarse deposited particles. Four pertinent soiling parameters were measured: total mass of deposited particles (by weighing), mass of total carbon (by thermo-coulometry), mass of water soluble ions (by ion chromatography on glass surface rinsing water) and haze (by spectrophotometry). Model fitting to experimental data showed a continuous increase of soiling in time, following a variable slope sigmoid (Hill equation) for all the four soiling parameters. This similar evolution allowed defining one general model for soiling.
Keywords: Particle deposition; Carbon; Salts; Optical glass properties; Hill equation;

In the present investigation, the rainwater chemistry is studied over a one year period at a regional representative urban site, Tirupati. A continuous record of 67 events were included that ranged from 0.5 to 74.6 mm (annual total 850.2 mm), from which 35 events (52%) were chemically analyzed during the period for major inorganic ion composition viz. F, Cl, NO3, SO4, Na, K, Ca, and Mg as well as NH4. The volume-weighted mean (VWM) of the measured ionic sum is 501.28 μeq l−1 and the crustal ion contribution dominating over the acidic ions with a ratio of total cation to that of anions (Σcations/Σanions) is 1.4. Only the Ca and SO4 together made up more than 55% of the total ion, whereas Ca alone contributed about 51% of the total cation. All the rain samples analyzed showed alkaline pH always, to that of reference level 5.6, with VWM of 6.78. On the basis of good correlation between the crustal ions (Ca, Mg, K and NH4) and SO4 ( r = 0.95 ) and NO3 ( r = 0.91 ) as well as order of neutralization factors Ca (0.88)>Mg (0.33)>NH4 (0.11), it has been determined that the acid neutralization is brought about by crustal ions, particularly calcium, in the region. The data were subjected for correlation analysis. A good correlation observed between Ca and SO4 and NO3 ( r = 0.92 and 0.90) and Mg and SO4 and NO3 ( r = 9.83 and 0.77), respectively, reveals that the ionic composition of rainwater in the region is strongly influenced by terrestrial sources rather than anthropogenic and marine sources.
Keywords: Chemical composition; Temporal variation; Acid neutralization; pH; Terrestrial sources; Precipitation;

Large decrease of VOC emissions of Switzerland's car fleet during the past decade: results from a highway tunnel study by Konrad Stemmler; Stefan Bugmann; Brigitte Buchmann; Stefan Reimann; Johannes Staehelin (1009-1018).
The emissions of 14 C4–C8 VOC species from road traffic have been measured in a highway tunnel (Gubristtunnel) near Zurich, Switzerland in 2002. The investigated traffic situation corresponds to highway driving with an average speed of 90 km h−1 and hot engine conditions. The comparison with measurements in the same tunnel performed in 1993 indicates that the emission factors of the individual hydrocarbons decreased on average by 80% in the 9 years between both investigations. This improvement can mainly be explained by the nearly complete elimination of non-catalyst gasoline-fuelled cars from the Swiss car fleet in the past decade. The relative emission strengths of the quantified individual VOCs were similar in 1993 and 2002. The emission factors reported in this study are the lowest reported from on-road vehicle emission measurements so far, indicating the efficient technology of modern car fleets with respect to VOC emissions. The emission factors derived from the tunnel study are compared to modelled emission factors based on dynamometric test measurements on Swiss passenger cars. The employed model is the Handbuch für Emissionsfaktoren des Strassenverkehrs; version 1.2 (Umweltbundesamt Berlin and INFRAS AG Bern, 1999). A good agreement between the modelled and measured emissions was found for the investigated traffic situation, indicating that the development of the VOC emissions during the last decade is well understood on the basis of the fleet composition and the dynamometric test measurements. The observed VOC emission reduction corresponds to a traffic situation, where an optimal exhaust gas catalyst performance can be expected. Factors leading to a somewhat less beneficial influence of the catalytic converter technique in other relevant driving situations are therefore additionally discussed.
Keywords: Hydrocarbons; Vehicle emissions; Benzene; Emission factors; Road traffic;

Historical trends of polycyclic aromatic hydrocarbons in the reservoir sediment core at Osaka by Hiroshi Moriwaki; Kenshi Katahira; Osamu Yamamoto; Joji Fukuyama; Toshikazu Kamiura; Hideo Yamazaki; Shusaku Yoshikawa (1019-1025).
The historical trends of polycyclic aromatic hydrocarbons (PAHs) in the sediment core of the moat in Osaka Castle, located at the center of Osaka city, Japan, were studied. The moats in Osaka Castle were built in the 1620s, and the undisturbed sediment core, which consists of atmospheric deposits in Osaka city from 1671 to 1976, was withdrawn from the moat. PAHs in the sediment core were identified and quantified in the total concentration range of 0.053–26 mg kg−1 dry wt. The highest content of PAHs was found in the sample, which was dated to 1944 during World War II. Osaka Castle was exposed to intense bombing raids during World War II, and the spiked peak of the PAH concentration during the mid-1940s was due to the air attacks. The total PAH concentration in the sediment core sample during World War II was about two-fold greater than the average after the war. This study made it appear that the largest impact of PAHs on the atmospheric environment in Osaka city in almost 300 years was caused by modern warfare.
Keywords: Osaka Castle; Moat; Deposit; World War II; Polycyclic aromatic hydrocarbon;

Formaldehyde levels in downtown Mexico City during 2003 by M. Grutter; E. Flores; G. Andraca-Ayala; A. Báez (1027-1034).
In this study, two spectroscopic techniques and two DNPH-sampling techniques were operated simultaneously in a downtown site of Mexico City to accurately determine formaldehyde levels during February and October of 2003. 1-hour samples from DNPH-silica cartridges and 4-h samples with an annular denuder system were collected during 4 days. The results are compared with the continuous data provided by an open-path Fourier transform infrared spectrometer (OP-FTIR) and a differential optical absorption spectrometer (DOAS) along a 426 m trajectory. Both spectroscopic techniques showed an agreement of 15% or less and a correlation coefficient of 0.86. The cartridge results presented average deviations relative to the OP-FTIR between −32% and 24% for the specific time periods but showed a clear similarity in the temporal patterns from the 5-min spectroscopic data. The results from the annular denuder samples show more limited precision (−35–65%) but the overall accuracy, when all data collected for the two 4-h periods was averaged, fell within a ±15% deviation range. This sampling configuration allowed to estimate an amount of formaldehyde in the particulate matter (<2.5 μm) of about 20% from that found in the gas-phase. Monthly average concentrations ranged between 23.9 ppb during February and 12.7 ppb during October of 2003. A 35% decrease in the average-peak values between the dry and wet seasons was identified.
Keywords: Formaldehyde; Mexico City; OP-FTIR; DOAS; DNPH samplers;

Three-dimensional survey of pollution during winter in French Alps valleys by Patrick Chazette; Pierre Couvert; Hariliva Randriamiarisoa; Joseph Sanak; Bernard Bonsang; Patricio Moral; Sébastien Berthier; Sophie Salanave; Franck Toussaint (1035-1047).
We developed and installed a scientific payload on-board an ultra-light aircraft dedicated to ozone, nitrogen oxides and aerosol-scattering profilers to study the spatial distribution of pollution in the Chamonix and Maurienne valleys (French Alps). Meteorological parameters (temperature, pressure and relative humidity) and altimetry (GPS measurements) were recorded simultaneously. A synergy of measurements has been ensured with a ground mobile station equipped with a new lidar emitting at 532 nm. The experiment undertaken in January 2003 during the daytime allowed us to document, for the first time, the pollution level on horizontal and vertical scales during typical winter situations in the Alps valleys. Our results show a strong inversion of temperature up to about 150±50 m above the valley bottom, in the Chamonix valley, which traps the pollutants close to the snow-covered surface. Their concentrations are thus closely linked to the proximity of their sources and seem to have a local influence. In the Maurienne valley, with a bottom surface mostly free of snow, more efficient mixing due to convection is observed and a multi-layer structure between the planetary boundary layer and the free troposphere is detected on lidar vertical profiles. These lidar measurements allow a characterization of valley aerosols, with a backscatter to extinction ratio of ∼0.028 sr−1 very close to the value retrieved during the INDian Ocean EXperiment for a mixing of aerosols from biomass and fossil fuel burning.
Keywords: Pollution; Airborne measurements; Alpine valleys; POVA; Ultra-light aircraft; Lidar;

A comparison of contaminant plume statistics from a Gaussian puff and urban CFD model for two large cities by Julie Pullen; Jay P. Boris; Theodore Young; Gopal Patnaik; John Iselin (1049-1068).
This paper quantitatively assesses the spatial extent of modeled contaminated regions resulting from hypothetical airborne agent releases in major urban areas. We compare statistics from a release at several different sites in Washington DC and Chicago using a Gaussian puff model (SCIPUFF, version 1.3, with urban parameter settings) and a building-resolving computational fluid dynamics (CFD) model (FAST3D-CT). For a neutrally buoyant gas source term with urban meteorology, we compare near-surface dosage values within several kilometers of the release during the first half hour, before the gas is dispersed beyond the critical lethal level. In particular, using “fine-grain” point-wise statistics such as fractional bias, spatial correlations and the percentage of points lying within a factor of two, we find that dosage distributions from the Gaussian puff and CFD model share few features in common. Yet the “coarse-grain” statistic that compares areas contained within a given contour level reveals that the differences between the models are less pronounced. Most significant among these distinctions is the rapid lofting, leading to enhanced vertical mixing, and projection downwind of the contaminant by the interaction of the winds with the urban landscape in the CFD model. This model-to-model discrepancy is partially ameliorated by supplying the puff model with more detailed information about the urban boundary layer that evolves on the CFD grid. While improving the correspondence of the models when using the “coarse-grain” statistic, the additional information does not lead to quite as substantial an overall agreement between the models when the “fine-grain” statistics are compared. The taller, denser and more variable building landscape of Chicago created increased sensitivity to release site and led to greater divergence in FAST3D-CT and SCIPUFF results relative to the flatter, sparser and more uniform urban morphology of Washington DC.
Keywords: Urban dispersion; Urban meteorology; Emergency response; Modeling;

Measurements of environmental 1,3-butadiene with pumped and diffusive samplers using the sorbent Carbopack X by Nicholas A. Martin; Philippa Duckworth; Malcolm H. Henderson; Nigel R.W. Swann; Simon T. Granshaw; Robert P. Lipscombe; Brian A. Goody (1069-1077).
Studies with the sorbent Carbopack X in pumped and diffusive samplers, of the Perkin–Elmer-type, have been carried out using a controlled atmosphere test facility (CATFAC) to generate 1,3-butadiene, together with benzene, at environmental levels. The 7-day and 14-day 1,3-butadiene diffusive uptake rates for this sorbent have been determined to be respectively (1.24±0.16) ng ppm−1  min−1 ((0.55±0.07) cm3  min−1)) and (1.02±0.12) ng ppm−1  min−1 ((0.45±0.05) cm3  min−1)) under a wide range of concentrations at 20 °C, 50% relative humidity and a wind speed of 1 m s−1. Preliminary studies indicate that this sorbent may also be useful in radial diffusive samplers for short-term monitoring over a few hours. A pumped sampling method has been developed to measure both 1,3-butadiene and benzene simultaneously over a period of 14-days using two Perkin–Elmer-type devices coupled to an in-house developed controlled flow air sampler. The 1,3-butadiene safe sampling volume for Carbopack X has been measured yielding a value of ⩽82 litre g−1. Tests carried out with calibrated amounts of 1,3-butadiene (50 ng and 150 ng) on Carbopack X indicate that samplers should be stored in a refrigerator prior to thermal desorption in order to achieve a recovery of effectively 100%. Ambient ozone does not appear to react with 1,3-butadiene adsorbed in the samplers.
Keywords: Diffusive uptake rate; Perkin–Elmer-type sampler; Radiello device; Safe sampling volume; Test atmosphere;

The total deposition of nitrogen was estimated at 10 plots in the Swiss Long-Term Forest Ecosystem Research Programme for 1 year (1999/2000) using two methods: (1) the throughfall method, using bulk precipitation and throughfall measurements as input data for the canopy budget model; and (2) the inferential method, based on measurements of ammonia and nitrogen dioxide with passive samplers and deposition velocities taken from literature. The inferential method was coupled with a regression model deriving the other terms of the total deposition of nitrogen (wet deposition, dry deposition of nitric acid and dry deposition of particulate nitrogen) from measurements of the bulk deposition of nitrogen. The two methods gave estimates of the total deposition that correlated significantly with each other, in the range of 5–38 kg ha−1  a−1, but the inferential method tended to yield higher estimates than those obtained with the throughfall method (median difference +2.4 kg ha−1  a−1). In view of the overall agreement of the two methods, the use of passive samplers in the open, coupled with the measurement of bulk deposition, appears, under certain conditions, to be an interesting alternative to the throughfall method.
Keywords: Total N deposition; Bulk deposition; Throughfall; Passive samplers; NO2; NH3;

Deriving an effective aerosol single scattering albedo from spectral surface UV irradiance measurements by A.F. Bais; A. Kazantzidis; S. Kazadzis; D.S. Balis; C.S. Zerefos; C. Meleti (1093-1102).
The modification of clear-sky global and diffuse irradiances and the direct-to-diffuse irradiance ratio by the aerosol single scattering albedo, ω , as a function of aerosol optical depth, τ a , and solar zenith angle (SZA) is investigated using radiative-transfer model calculations. The model-derived relations are combined with UV irradiances at the surface and the aerosol optical depth measured with a Brewer MkIII spectroradiometer, with the aim to develop and test an indirect method of estimating an effective single scattering albedo. The uncertainties introduced from different sources are quantitatively discussed in order to determine the overall uncertainty of the method. The overall accuracy in determining ω indirectly depends strongly on the radiation quantity used and the amount of aerosols, increasing the uncertainty of the method in situations with τ a at 340 nm below 0.2. From the three radiation quantities, the direct-to-diffuse irradiance ratio provides the highest accuracy in the estimation of the effective ω . As an example, the effective ω is determined for 2 days with different aerosol loadings and composition. Finally, 5 years of measurements of global irradiance and τ a under cloud-free conditions are analysed in order to estimate the range of variation of the effective ω at Thessaloniki, Greece. For τ a at 340 nm larger than 0.8, ω ranges between 0.85 and 0.99, while for lower-aerosol optical depths the derived effective ω covers the entire range from 0.64 to 0.99.
Keywords: Aerosol optical properties; Single scattering albedo; UV irradiance;

Characterization of malodorous sulfur compounds in landfill gas by Ki-Hyun Kim; YJ Choi; EC Jeon; Young Sunwoo (1103-1112).
In order to analyze the composition of landfill gas (LFG) with respect to malodorous components, the concentrations of several reduced sulfur compounds (RSC: hydrogen sulfide (H2S); methyl mercaptan (CH3SH); dimethyl sulfide ((CH3)2S); carbon disulfide (CS2); and dimethyl disulfide ((CH3)2S2)) were determined from four municipal landfill sites—initialed W, B, H, and N—in Korea. The S gas concentrations measured in these landfill sites were found consistently to be dominated by H2S, while their absolute mean values tended to change considerably between one inactive site (N) and the others; its mean values were measured from as little as 336 ppb (N site) up to 2340 ppm (H site). Hence, in terms of mass concentration units (mg m−3), H2S alone generally explained far more than 90% of all S gases determined concurrently. If the relative contribution of RSC to the LFG budget is assessed in relation to major aromatic hydrocarbons (e.g., benzene, toluene, and xylene), the RSC emission appears to comprise a significant proportion as trace components of LFG other than major ones like CH4 and CO2.
Keywords: Hydrogen sulfide; Sulfur gas; Malodor; VOC; Landfill;

Hydrocarbon concentrations at the Alpine mountain sites Jungfraujoch and Arosa by Yingshi Li; Mike Campana; Stefan Reimann; Daniel Schaub; Konrad Stemmler; Johannes Staehelin; Thomas Peter (1113-1127).
Volatile hydrocarbons have been measured for 1 yr at Arosa (2010 m asl) to determine the contribution of European emissions to the trace gas concentrations at this remote site. Results are compared to concurrent hydrocarbon concentrations at the high Alpine background site Jungfraujoch (3580 m asl). Hydrocarbon concentrations at Arosa are generally much higher than at Jungfraujoch. The influence of the Alpine boundary layer air was studied based on the diurnal variation of hydrocarbon concentrations, i.e. rising pollutant concentrations in the morning at Arosa and in the afternoon at Jungfraujoch. Different hydrocarbon emission sources of the uplifting air were found at the two sites. At Jungfraujoch, several transatlantic events were detected from October 2001 to January 2002 based on analysis of hydrocarbon ratios and air parcel trajectories. The OH concentration during the transatlantic transport was estimated to be around 5×105  cm−3, derived from simultaneous hydrocarbon oxidation and dilution in the free troposphere. These transatlantic transport events were tracked back to warm conveyor belts, characterized by uniform dynamics and relatively uniform surface sources. In addition, ozone production in the free tropospheric transport was also documented in these events.
Keywords: Intercontinental transport; Alpine air flow; Trajectories; OH concentration;

Impact of climate change on surface ozone and deposition of sulphur and nitrogen in Europe by Joakim Langner; Robert Bergström; Valentin Foltescu (1129-1141).
The potential impact of regional climate change on the distribution and deposition of air pollutants in Europe has been studied using a regional chemistry/transport/deposition model, MATCH. MATCH was set up using meteorological output from two 10-year climate change experiments made with the Rossby Centre regional Atmospheric climate model version 1 (RCA1). RCA1 was forced by boundary conditions from two different global climate models using the IPCC IS92a (business as usual) emission scenario. The global mean warming in both the GCMs was 2.6 K and was reached in the period 2050–2070. Simulations with MATCH indicate substantial potential impact of regional climate change on both deposition of oxidised nitrogen and concentrations of surface ozone. The simulations show a strong increase in surface ozone expressed as AOT40 and mean of daily maximum over southern and central Europe and a decrease in northern Europe. The simulated changes in April–September AOT40 are significant in relation to inter-annual variability over extended areas. Changes in deposition of oxidised nitrogen are much smaller and also less coherent due to the strong inter-annual variability in precipitation in the RCA1 simulations and differences in the regional climate change simulated with RCA1 in the two regional scenarios. Changes in simulated annual deposition are significant in relation to inter-annual variability only over small areas. This indicates that longer simulation periods are necessary to establish changes in deposition.
Keywords: Climate change; Regional air pollution; Scenarios; Sulphur and nitrogen deposition; Ozone;

The chemical mechanism generation programme CHEMATA (CHEmical Mechanism Adaptation to Tropospheric Applications) generates explicit or lumped gasphase chemical mechanisms. Input data are a list of species and their source strengths (emissions or atmospheric production), kinetic data and lumping group definitions. All these input data can be changed by the user in order to generate a mechanism which is adapted to the needs of the user and to the conditions of the modelling area. The programme converts the information about the chemical structure of each species into a number code which contains all necessary information about the atoms of this molecule and the way they are connected to each other. For describing a chemical reaction the code is modified in a well-defined way which corresponds to the change in the molecule structure which in reality occurs during this reaction. This number code is also used to identify species for which experimental kinetic data are available or for employing structure–reactivity relationships for estimating kinetic data. To enable lumping to be as flexible as possible all organic mechanism species can be defined by their functional groups, their reactivity, and their chain lengths. CHEMATA compares these definitions with the number codes of the real species in order to determine the correct lumping group for each real species. Then the lumped mechanism is produced considering the source strengths of all real species. As an application of CHEMATA two sensitivity studies were performed: one on the influence of species lumping by extending and reducing the regional atmospheric chemistry mechanism and the other on the influence of updating the kinetic data for the kinetics of oxy radical reactions.
Keywords: Air quality modelling; Lumped mechanism; Tropospheric ozone; Gasphase chemistry; Mechanism generation;

RACM and the three new mechanisms described in the companion paper (the extended, reduced and small mechanisms) are implemented in a mesoscale 3D transport-chemistry model (TAPOM for Transport and Air POllution Model) in order to find an optimum between calculation speed and mechanism detail. The 3D tests are performed in the domains of Milan, Mexico City and Bogota. The three domains present different chemical and meteorological conditions, which are used to test the behaviour of the four mechanisms in different situations. Three emission scenarios are simulated: the whole emission inventory, 35% NO x reduction and 35% VOC reduction. The comparison of the four mechanisms is performed for O3, NO x , aldehydes and peroxy radicals. Only the small mechanism presents significant differences in ozone concentrations. RO2 and aldehyde differences are important with the reduced and the small mechanism, which share a new RO2 parameterisation. Compared to RACM, the small mechanism shows very large differences for aldehydes and RO2. The extended mechanism and RACM show almost the same ozone response to emissions reduction strategies, and the reduced mechanism presents differences in the range of 10% with respect to the extended mechanisms. The small mechanism is found to be the most VOC sensitive and therefore presents very different results from the other when emissions are modified. The results indicate a strong restriction to the use of the small mechanism in 3D models. Finally, the calculation time required for the calculation of a simulation with the four mechanisms is compared.
Keywords: Mesoscale modelling; Tropospheric chemistry; Chemical mechanism generation; VOC lumping; Emissions reduction strategies;

Brochosomes are excitingly shaped hollow spherical particles produced by leafhoppers (Cicadelliae), presumably to serve as a very efficient water-repellent protective surface coating. The spheroids have a diameter between 250 and 600 nm and are made of a network of protein–lipid rods, arranged in the form of hexagons and pentagons. Brochosomes in the atmosphere have been described only a few times and the reported concentrations were usually small. The cause of the apparently rare occurrence of these particles in ambient air is shown to be twofold. First, most of the brochosomes are airborne not as individual species, but in the form of rather large clusters containing up to 100,000 particles. Second, for high-efficiency collection of particles with aerodynamically complex morphology such as brochosomes (or agglomerates of carbon nanoparticles), size selective sampling with impactors turned out to be more efficient the higher the nozzle velocity. In a series of sampling campaigns brochosomes were found to be the most abundant bioaerosol particles in a semi-urban atmosphere during the warm season. Occasionally, brochosomes tended to react with other nanoparticle matter. As a result, the presumably freshly produced brochosomes became strongly distorted, rearranging in a variety of exotic forms, including perfect or distorted domes or even a spider web.
Keywords: Brochosome; Bioaerosol; Scanning electron microscopy; Impactor;