Atmospheric Environment (v.39, #28)

This work investigates the turbulent flow and dispersion of atmospheric contaminants in the vicinity of an isolated building. Field experiments were carried out to measure the fluctuating concentration time-series on the walls of a complex-shaped building, and to investigate the influence of atmospheric stability and building dimensions on certain statistics of the concentration distribution on the walls of the building. Meteorological conditions varied from neutral to unstable. The measurements were conducted for two different wind directions (west and south, corresponding respectively to directions normal and parallel to the long axis of the building). The experiments were performed in flat terrain with uncut vegetation. The gas detectors used were photo ionisation detectors (PIDs) with a response time of approximately 1/50 s. Sixteen such detectors were deployed, with 14 located on the building walls, and 2 on the roof. The analysis presented here is for the 14 detectors on the walls. Statistical parameters of the concentration time-series and the wind flow are presented, including mean and standard deviation. Intermittency and concentration fluctuation intensity are also presented. Results were analysed based on the turbulent structures of the fluid flow around the building. The experimental work revealed that the atmospheric stability conditions significantly influenced the concentration levels on the external walls of the building, except on the windward wall. It was also revealed that mean conditional concentration values on the walls were significantly influenced by the ratio between building width and height.
Keywords: Field experiments; Building effects; Concentration fluctuation; Stability conditions;

Driving forces for ammonia fluxes over mixed forest subjected to high deposition loads by J. Neirynck; A.S. Kowalski; A. Carrara; R. Ceulemans (5013-5024).
Ammonia exchange was measured over a mixed suburban forest near a rural area. An average net ammonia flux of −90 ng m−2  s−1 was measured with corresponding concentration ([NH3]) and deposition velocity of 4.1±6.5 μg m−3 and 3.0±4.6 cm s−1, respectively. Subdivision into categories of day/nighttime, wind sector and canopy wetness helped explain fluxes and concentrations. Net fluxes were approximately double for the wind sector exposed to high ammonia levels and during the day. To a certain extent, fluxes (F) followed the maximum flux permitted by turbulent transfer (F max), which was the highest for a dry canopy. When expressed as relative deposition flux ( F / F max x ), a wetted canopy seemed to be a more efficient sink than a dry one, especially at nighttime (20–80% increase compared to dry canopy).Of the net fluxes, 14% represented emission. Emission fluxes occurred mainly during daytime and were important in magnitude for the high [NH3] wind sector. Emission episodes generally occurred at low ammonia concentrations although high concentrations during dry, warm episodes were also associated with emission events.The lower deposition efficiency and higher canopy resistance (R c) at high ammonia levels and at night were indicative of the reduced capacity for leaf surface to retain ammonia, especially when the canopy was dry. It was found that relative humidity (RH) and temperature (T) strongly codetermined the sink strength of the canopy. A warm and humid atmosphere favoured ammonia uptake while conditions with low RH and T impeded rapid canopy uptake, especially at high ammonia levels. Strong interactions between RH and T with the (NH3/SO2) molar ratio occurred for certain categories of canopy wetness and day/nighttime. Canopy uptake was further optimized when this ratio was maintained within a certain range.
Keywords: Co-deposition; Emission; Net ammonia flux; Canopy wetness; Canopy resistance; Sulphur dioxide;

A parameterization for the dry deposition of SO2 is evaluated by means of four statistical sensitivity studies using a sampling-based approach to sensitivity analysis. Measurements over a heathland, grassland and coniferous forest are used to identify those meteorological and vegetation-specific factors which drive the deposition component of the model (model-based studies) and which are most important in the determination of model-measurement discrepancies. Sensitivity indices and scatter plots for monthly average fluxes indicate that the dominant factors are for most months related to non-stomatal components of the deposition flux.
Keywords: Dry deposition; Non-stomatal resistance; Latin hypercube sampling; Dominant factors; Scatter plots; Sensitivity indices;

First aerosol optical thickness measurements at Dome C (East Antarctica), summer season 2003–2004 by Delphine Six; Michel Fily; Luc Blarel; Philippe Goloub (5041-5050).
In the framework of a calibration project concerning satellite sensors over a remote site of inland Antarctica, the temporal variations of atmospheric aerosol properties have been investigated in relation to their strong influence on the transfer of visible radiation. For this, a sunphotometer was installed at Concordia station (75°S, 123°E, 3200 m a.s.l.) on the Antarctic plateau during summer season 2003–2004. Meteorological parameters were recorded for the same period. Very low aerosol optical thickness values were observed with a mean AOT of 0.02 at 440 nm and 0.007 at 870 nm for clear sky conditions, and a small standard deviation. Angstrom coefficients were high with an average of 1.65 at 440 nm. These values reflect the high purity of the atmosphere and the small size of particles, mainly sulfate aerosols. Higher AOT values are observed under diamond dust conditions (0.025 at 440 nm and 0.013 at 870 nm). Temporal variations are also observed at the daily and seasonal levels. Dome C, therefore, appears to be an excellent site for satellite sensor calibration as well as investigations concerning the background atmospheric composition and global atmosphere changes caused by human activities.
Keywords: Aerosols; Antarctica; Sunphotometer; Optical thickness; Angstrom coefficients;

Trifluoro methyl peroxynitrate (CF3OONO2): Temperature dependence of the UV absorption spectrum and atmospheric implications by Fabio E. Malanca; Malisa S. Chiappero; Gustavo A. Argüello; Timothy J. Wallington (5051-5057).
The ultraviolet absorption spectrum of gas phase CF3OONO2 has been measured over the wavelength range 200–340 nm at 233–300 K. Absorption cross-sections at wavelengths of 290–340 nm were found to increase significantly with increasing temperature. The UV spectra of CF3C(O)Cl and CF3C(O)F were measured and were consistent with previous work [Rattigan et al., 1993. Temperature-dependent absorption cross-sections of CF3COCl, CF3COF, CH3COF, CCl3CHO and CF3COOH. Journal of Photochemistry and Photobiology A: Chemistry 73, 1–9]. Implications for the atmospheric chemistry of CF3OONO2 are discussed.
Keywords: UV absorption; CF3OONO2; Atmosphere; Peroxynitrates; Peroxides;

The concentrations and composition of and exposure to fine particles (PM2.5) in the Helsinki subway system by Päivi Aarnio; Tarja Yli-Tuomi; Anu Kousa; Timo Mäkelä; Anne Hirsikko; Kaarle Hämeri; Mika Räisänen; Risto Hillamo; Tarja Koskentalo; Matti Jantunen (5059-5066).
 Fine particulate matter (PM2.5) and particle number concentrations were monitored in the Helsinki subway system during a two-weeks’ measurement campaign in March 2004. The PM2.5 samples was analysed for elemental composition and carbon fraction. The average daytime PM2.5 concentrations were 47 (±4) and 60 (±18) μg m−3 at the two underground subway stations and 19 (±6) and 21 (±4) μg m−3 at a ground level station and in subway cars, respectively. For the same measurement period, the corresponding PM2.5 concentrations at the urban background and street canyon monitoring sites were 10 (±7) and 17 (±10) μg m−3.The particle number (D<500 nm) concentrations and size distributions at the underground subway station were very similar to those measured at the urban background monitoring site indicating that the source of particles of this size is street traffic. The average daytime particle number concentration was 31 000 (±14 000) particles cm−3 compared to 27 000 (±17 000) particles cm−3 at an urban background monitoring site (D<320 nm). The average daytime black carbon concentration was 6.3 (±1.8) μg m−3, the concentration of elemental carbon 4.0 (±2.0) and organic carbon 7.4 (±1.6) μg m−3.The most enriched element in PM2.5 samples was iron, the concentration of which ranged from 0.7 (±0.3) μg m−3 at the ground level subway station to 29 (±7) μg m−3 at the underground subway station. Other enriched elements included Mn, Cr, Ni, and Cu. We calculated that 30 min commuting +9 min stay at the stations per day increased the exposure to PM2.5 mass by only approximately 3% compared to staying in urban traffic environment, but the exposure to iron in PM2.5 increased nearly 200%, to Mn 60%, and to Cu 40%.
Keywords: PM2.5; Particle number concentration; Elemental composition; Carbon analysis; Subway; Exposure;

Planetary boundary layer (PBL) ozone densities, retrieved from ozone soundings at Uccle (Belgium) and Payerne (Switzerland) between 1990 and 2000 are analysed. This PBL ozone is representative on a regional scale, also in highly polluted areas. At Uccle the yearly cycle of PBL ozone shows late spring and summer maxima, while in Payerne one broad summer maximum with peak in July is present. An overall and a composite multiple linear regression model has been built using meteorological and NO x data as independent variables. For Uccle and Payerne the explained variances for the composite models were 63.43% and 78.97% with an rmse of 15.95 μ g m - 3 and 16.50 μ g m - 3 , respectively. Both stations have an overall significant negative trend during the time period 1997–2000. During winter and autumn there is a positive significant trend present for Payerne and Uccle, which is explained by a decrease in NO x concentrations. For some particular days dynamical effects are illustrated with 10 day 3D backwards trajectories. This shows that further improvement can only be achieved by including chemical and dynamical effects in the models.
Keywords: Tropospheric ozone; Ozonesonde; Model; Boundary layer; Trends;

Soot particles in the free troposphere over Australia by Kikuo Okada; Miwako Ikegami; Yuji Zaizen; Yukitomo Tsutsumi; Yukio Makino; Jorgen B. Jensen; John L. Gras (5079-5089).
Aircraft observations were carried out in the middle troposphere at 5–6 km altitude over Australia in the PACE-II (Pacific Atmospheric Chemistry Experiment) campaign in October 1994. Concentrations of particles with radii larger than 4 nm and 0.15 μm were measured with a condensation nucleus (CN) counter and an optical counter, respectively. Individual aerosol particles were collected on electron microscopic grids using a jet impactor and subsequently examined using a transmission electron microscope coupled with an energy-dispersive X-ray (EDX) analyzer.High concentrations of CN (⩾4 nm) and large particles (0.15–0.5 μm radius) were found over the areas in northern Australia between Alice Springs and Darwin. Samples collected in this region had a large fraction of submicrometer soot-containing particles that had both K and S with a median S/(S+K) weight ratio of 0.4. The hygroscopic properties of particles with radii between 0.03 and 0.8 μm were examined with the dialysis (extraction) of water-soluble material. The sample collected in the area with high particle concentrations showed that the abundance of internally mixed soot particles was 88% of particles in the radius range of 0.1–0.35 μm. Approximately 50% of these mixed particles with radii ⩾0.2 μm were covered with semi-transparent material (probably organic material). Present research suggested that these particles were aged biomass burning particles originating from northern Australia and had been modified by chemical reactions and probably by coagulation during long-range transport. These soot particles were found to be present as internally mixed particles, with a soluble fraction that would make them efficient cloud condensation nuclei (CCN).
Keywords: Soot particles; Australia; Biomass burning; Free troposphere; Mixing properties; Single particle analysis;

Influence of temperature in the kinetics of the gas-phase reactions of a series of acetates with Cl atoms by Carlos A. Cuevas; Alberto Notario; Ernesto Martínez; José Albaladejo (5091-5099).
Absolute rate coefficients have been measured for the first time as a function of temperature for the gas phase reactions of chlorine atoms with a series of aliphatic acetates: methyl acetate ( k 1 ), ethyl acetate ( k 2 ), n -propyl acetate ( k 3 ) and n-butyl acetate ( k 4 ). The experiments were carried out using the pulsed laser photolysis-resonance fluorescence technique (PLP-RF), over the temperature range 265–383 K. The obtained kinetic data were used to derive the Arrhenius expressions: k 1 = ( 9.31 ± 1.02 ) × 1 0 - 12 exp [ - ( 359 ± 70 ) / T ] ; k 2 = ( 4.35 ± 0.65 ) × 1 0 - 12 exp [ ( 342 ± 92 ) / T ] ; k 3 = ( 2.22 ± 0.20 ) × 1 0 - 11 exp [ ( 217 ± 58 ) / T ] and k 4 = ( 5.41 ± 1.51 ) × 1 0 - 11 exp [ ( 245 ± 168 ) / T ] (in units of cm3  molecule−1  s−1). The rate constants obtained at room temperature were as follows: methyl acetate, 0.279±0.031; ethyl acetate, 1.37±0.20; n -propyl acetate, 4.60±0.41 and n -butyl acetate, 12.3±3.4 (in units 10−11  cm3  molecule−1  s−1). The results are discussed in terms of structure-reactivity relationships and the atmospherics implications are also analyzed.
Keywords: Atmospheric chemistry; Chlorine atoms; Gas-phase reaction; Laser photolysis; Esters;

Evaluation of the TMO and TOT methods for OC and EC measurements and their characteristics in PM2.5 at an urban site of Korea during ACE-Asia by Seung Shik Park; Min S. Bae; James J. Schauer; Seong Y. Ryu; Young J. Kim; Sung Yong Cho; Seung Jai Kim (5101-5112).
Daily fine particle (PM2.5) samples, collected during 2001 ACE-Asia at an urban site of Gwangju, Korea, were analyzed for their organic and elemental carbon (OC and EC) concentrations using thermal–optical transmittance (TOT) and thermal manganese dioxide oxidation (TMO) protocols. The goals of this paper were to evaluate the difference in the OC and EC measurements using two different carbon speciation protocols, and investigate the characteristics of carbonaceous particles in relation to the origins of air parcels.The TMO and TOT as operated in the NIOSH method, have been shown to provide equivalent results for total carbon (TC), with a slope of 0.95 and R 2 of 0.995, but the TMO provides a 9% higher OC and 20% lower EC than the TOT protocol. Importantly, however, combining our results with those of previous comparison studies, between IMPROVE thermal–optical reflectance (TOR) and NIOSH TOT [Chow et al., 2001. Aerosol Science and Technology 34, 23–34], and between TMO and TOR [Fung et al., 2002. Journal of the Air and Waste Management Association 52, 1333–1341], together demonstrate that the nature of the collected samples, in terms of loading, OC/EC ratio and particle composition can significantly affect the analytical results.The origins of air mass pathways arriving at the sampling site, calculated using the HYSPLIT backward trajectory model, can be mostly classified into five types: northwestern China (Type I, i.e. representing clean condition); western/or southwestern marine (Type II); southern marine (Type III); northwestern China, with Asian dust particles (Type IV); and northeastern China, passing through northern Korea (Type V). When an air mass originating from northeastern China passed through the Korean peninsula (Type V), the OC concentrations were the most elevated, with a higher OC/EC ratio (2.7), and accounting for 20.7% of PM2.5 mass on average. However, when the air mass originated from the northwestern China desert regions during Asian dust events (Type IV), the average OC and EC concentrations were 4.6 and 2.1 μg C m–3, respectively, accounting for only 6.7% and 3.1% of the PM2.5 mass, which was due to the huge dust input, resulting in a much elevated PM2.5 mass. Also, a lower black carbon (BC)/carbon monoxide (CO) slope was observed for the air masses originating from the northwestern Chinese regions, which had traveled through Chinese coastal industrial areas and over the Yellow Sea (Types I and IV), than in those originating from marine (Types II and III) or northeastern Chinese (Type V) regions, which had then passed over the Korean peninsula prior to reaching the measurement site.
Keywords: ACE-Asia; Carbonaceous particles; PM2.5; Asian dust;

Characteristics of vertical profiles and sources of PM2.5, PM10 and carbonaceous species in Beijing by C.Y. Chan; X.D. Xu; Y.S. Li; K.H. Wong; G.A. Ding; L.Y. Chan; X.H. Cheng (5113-5124).
In August 2003 during the anticipated month of the 2008 Beijing Summer Olympic Games, we simultaneously collected PM10 and PM2.5 samples at 8, 100, 200 and 325 m heights up a meteorological tower and in an urban and a suburban site in Beijing. The samples were analysed for organic carbon (OC) and elemental carbon (EC) contents. Particulate matter (PM) and carbonaceous species pollution in the Beijing region were serious and widespread with 86% of PM2.5 samples exceeding the daily National Ambient Air Quality Standard of the USA (65 μg m−3) and the overall daily average PM10 concentrations of the three surface sites exceeding the Class II National Air Quality Standard of China (150 μg m−3). The maximum daily PM2.5 and PM10 concentrations reached 178.7 and 368.1 μg m−3, respectively, while those of OC and EC reached 22.2 and 9.1 μg m−3 in PM2.5 and 30.0 and 13.0 μg m−3 in PM10, respectively. PM, especially PM2.5, OC and EC showed complex vertical distributions and distinct layered structures up the meteorological tower with elevated levels extending to the 100, 200 and 300 m heights. Meteorological evidence suggested that there exist fine atmospheric layers over urban Beijing. These layers were featured by strong temperature inversions close to the surface (<50 m) and more stable conditions aloft. They enhanced the accumulation of pollutants and probably caused the complex vertical distributions of PM and carbonaceous species over urban Beijing. The built-up of PM was accompanied by transport of industrial emissions from the southwest direction of the city. Emissions from road traffic and construction activities as well as secondary organic carbon (SOC) are important sources of PM. High OC/EC ratios (range of 1.8–5.1 for PM2.5 and 2.0–4.3 for PM10) were found, especially in the higher levels of the meteorological tower suggesting there were substantial productions of SOC in summer Beijing. SOC is estimated to account for at least 33.8% and 28.1% of OC in PM2.5 and PM10, respectively, with higher percentages at the higher levels of the tower.
Keywords: Particulate matter; Urban air pollution; Emission source; Atmospheric stability;

An analysis of the 12-month running means of CO (carbon monoxide) concentrations at various latitude belts during the 13 years 1989–2001 indicated oscillations with peak spacings in the QBO, QTO (quasi-biennial and quasi-triennial oscillations, 2–3 and 3–4 year) ranges. For middle and high northern latitudes, the QBOs of CO almost resembled the QBO of stratospheric low latitude winds. For other latitudes, there was no similarity with stratospheric winds. CO had a significant QTO in the range 3.0–3.3 years, but it did not match well with the major periodicity of ENSO (El Niño/Southern oscillation) at 4.3 years. The relative importance of the two mechanisms proposed by Hamilton and Fan [Journal of Geophysical Research 105 (2000) 20581–20587], namely the transport mechanism (dynamic stratospheric QBO modulating the interannual variations of long-lived tropospheric constituents) and the ozone mechanism (stratospheric QBO, affecting stratospheric ozone, affecting the UV radiation filtering down, affecting OH radical in the troposphere, affecting CO) is discussed. Both mechanisms seem to be partly operative in some latitudes.
Keywords: Quasi-biennial oscillation (QBO); Quasi-triennial oscillation (QTO); Carbon monoxide;

Country to country transport of anthropogenic sulphur in Southeast Asia by M. Engardt; U. Siniarovina; N.I. Khairul; C.P. Leong (5137-5148).
The MATCH model—driven by archived meteorological data from the ECMWF—has been used to study the long-range transport of pollutants in Southeast Asia during the year 2000. We have specifically investigated the atmospheric export and import of anthropogenic sulphur between nine countries in Southeast Asia as well as the import to these countries from the boundaries of our model domain, from southern China, and from international shipping in the surrounding waters.Compared to the conditions at the mid-latitudes (Europe, North America and East Asia), we find less long-range transport in this part of the world. In all countries in the region (except those with very small area, i.e. Singapore and Brunei), did the major part of the domestic emissions (60–70%) fall down on the emitting country itself. The fraction of the countries own emissions contributing to the total, annually accumulated, national deposition varied from 10% for Laos—which is a country with small emissions neighbouring large emitters—to 80–90% in countries not surrounded by significant emitters (i.e. Thailand, Indonesia, Singapore and Brunei).Sensitivity tests were performed to explore the uncertainties in the model simulations and to investigate to what extent the current results could be used for source–receptor relationships in the future, when the magnitude and location of the emissions may be different. We found that the general feature—with relatively little long-range transport of sulphur—will not be altered, while the absolute magnitude of the deposition in areas downwind of large emitters could change considerably if certain model parameters, or the emission patterns are changed. This is particularly true in light of the seasonal variation of the deposition pathways. The atmospheric import of anthropogenic sulphur from specific countries can vary by an order of magnitude between different months. Incidentally, a decrease in import from one country during a certain period is often compensated by a roughly equal increase of the import from another country during the same time.
Keywords: Acid deposition; Long-range transport; Malaysia; MATCH; Source–receptor relationships; Thailand;

Phase partitioning of atmospheric formaldehyde in a suburban atmosphere by Mustafa Odabasi; Remzi Seyfioglu (5149-5156).
Ambient air samples ( n = 89 ) were collected between May 2003 and May 2004 in Izmir, Turkey to investigate the gas/particle partitioning of formaldehyde (HCHO). Average gas-phase formaldehyde (HCHO) concentrations (7.3±6.5 μg m−3, average±SD) were within the range previously measured at different sites around the world. Particle-phase HCHO concentrations ranged between 3 and 65 ng m−3 (average±SD, 18±12 ng m−3) and HCHO was primarily associated with gas phase (99.55%).The partitioning of HCHO between particle and gas phases was compared to the absorptive gas/particle partitioning model. The partitioning model significantly underpredicted the experimental log K p (gas/particle partition coefficient) values. Modeled K p values were more than five orders of magnitude smaller than the experimental ones. However, the agreement between experimental K p values and those predicted for HCHO hydrate was very good, suggesting that HCHO hydrate formation in particles may be responsible for the measurement of anomalously large experimental K p values for HCHO.
Keywords: Formaldehyde; Gas–particle partitioning; Supercooled liquid vapor pressure;

Using NO x and CO monitoring data to indicate fine aerosol number concentrations and emission factors in three UK conurbations by I.D. Longley; D.W.F. Inglis; M.W. Gallagher; P.I. Williams; J.D. Allan; H. Coe (5157-5169).
It is increasingly accepted that although exposure to elevated concentrations of PM10 is associated with an increased risk of mortality and morbidity, the relationship may not be causal. Rather, there is evidence that number concentrations may be a more appropriate metric than mass concentrations in evaluating health risk. Number concentrations are not routinely monitored and spatial and temporal patterns are poorly quantified. CO and NO x are co-pollutants with their major urban source in common with fine particles, i.e. road vehicle emissions; are routinely monitored in many cities and are also related to ill health. Datasets of particle number concentration measurements from approximately month-long field campaigns in Manchester, Edinburgh and Birmingham (UK) are compared with simultaneous concentrations of CO and NO x from nearby fixed monitors. It was found that it might be possible to reliably predict particle number concentrations (diameters>100 nm) on an hourly basis in Manchester city centre from knowledge of NO x or CO concentrations alone. The influences of meteorology, spatial variability in emissions and lack of co-location upon the correlations are investigated using cluster analysis. The cluster analysis revealed that these relationships may vary between cities and are dependent upon monitor location but in ways that can be ascribed. For two out of three sites there existed a linear relationship between average cluster aerosol and gas concentrations. This indicates that although airmass aging disrupts the short-term linear relationship, the relationship in the average survives. An emission ratio of particles (approx. 100–500 nm diameter) to NO x of approximately 50 cm−3  ppb−1 was estimated in Manchester and Birmingham. Particle mass spectrometry measurements indicated that organic compounds dominated these particles and an emission rate of 0.58 ton km−2  a−1 of organic particulate matter from road transport has been estimated for the Greater Manchester conurbation.
Keywords: Urban atmosphere; Fine particles; Carbon monoxide; Oxides of nitrogen; Emission factors; Organic particles;

In this study we examined the co-formation of hydrogen peroxide and other hydroperoxides (collectively presented as H2O2*) as well as submicron particles, including ultra-fine particles (UFP), resulting from the reactions of ozone (O3) with a complex mixture of volatile organic compounds (VOCs) under simulated indoor conditions. The VOC mixture contained 23 compounds, including two terpenes (d-limonene and α-pinene), two unsaturated alkenes (1-decene and 1-octene), and 19 other saturated organic compounds. These compounds are commonly found in indoor air but their concentrations were higher than typical indoor levels. When O3 was added to a 25-m3 controlled environmental facility (CEF) containing the 23 VOC mixture, both H2O2* and submicron particles were formed. The 2-h average concentration of H2O2* was 1.89±0.30 ppb, and the average total particle number concentration was 46,000±12,000 particles cm−3. A small increase of UFP (0.02–0.1 μm) occurred 5 min after the O3 addition (17 min after the VOC addition) and a sharp increase of UFP occurred 13 min after the O3 addition, suggesting homogeneous nucleation. The delayed onset of this event might reflect the time required to achieve saturated concentrations of the condensable organics. When the 2 terpenes were removed from the O3/23 VOCs mixture, no H2O2* or particles were formed, indicating that the reactions of O3 with the two terpenes were the key processes contributing to the formation of H2O2* and submicron particles in the O3/23 VOCs system. The present study confirmed the findings of a previous study carried out in a real-world office and generated new findings regarding co-formation of UFP. Through a comparative analysis of H2O2* yields under different reaction conditions, this study demonstrates that VOCs co-present with the terpenes and O3 may play a role in producing H2O2*.
Keywords: Hydrogen peroxide; Secondary organic aerosols; Terpenes; Indoor chemistry; Homogenous nucleation;

Air pollution due to pesticides is a persistent problem in modern agriculture, and little is known on the reversibility of its effects on the environment and health. Pesticides contaminate the atmosphere through various pathways. This paper discusses techniques for measuring and modelling pesticide emission, and the factors that affect drift processes during spray application. Chemical analyses allow the concentration of polluting agents in the air to be measured, and different methods have been developed for measuring diverse pesticide groups. Several air-sampling methods, which give different results depending on the amount of air collected, are reported. The use of various tracers, such as fluorescent dyes, is widely reported. Brilliant sulphoflavine is the best fluorescent dye due to its low degradation in sunlight. Various collector devices are used, the most common being 2 mm diameter polymer lines. Although the report indicates a good level of collection efficiency, a complete understanding of the adhesion phenomenon is necessary. The use of mathematical and computational models to determine pesticide transport simplifies test and field evaluation. However, a detailed characterization of the agricultural environment, with temporal and spatial variations, is still necessary. The most common models are limited to transport and deposition of pesticides in the liquid phase to areas adjacent to treated fields. Drifting spray is a complex problem in which equipment design and application parameters, spray physical properties and formulation, and meteorological conditions interact and influence pesticide loss.
Keywords: Pesticide application; Drift; Measuring; Modelling; Environmental factors;

Passive sampling of atmospheric organochlorine compounds by SPMDs in a remote high mountain area by Barend L. Van drooge; Joan O. Grimalt; Kees Booij; Lluis Camarero; Jordi Catalan (5195-5204).
Semi-permeable membrane devices (SPMDs) have been deployed in high mountain areas (Central Pyrenees, Catalonia, Spain) for the measurement of atmospheric concentrations of hexachlorobenzene (HCB) and polychlorobiphenyls (PCBs) over a period of 1.5 years. These devices were filled with triolein and have been deployed at three altitudes, 1600, 2240 and 2600 m above sea level. Performance reference compounds were used to calibrate their sampling rates. The SPMD results were validated by comparison to active air sampling with high-volume systems. Sampling rates between 0.55 and 1.3 m3  d−1 were estimated from the dissipation of PCB155. Atmospheric concentrations measured by SPMDs were in good agreement with the levels obtained by high-volume sampling. These findings suggest that SPMDs can be useful monitoring systems for the atmospheric concentrations of organochlorine compounds in remote high mountain areas.

Aerosol particles reduce the electrical conductivity of air, through removal of the small ions causing the conductivity. Visual range is also affected by aerosol. Early 20th century work linked increased smoke pollution concentrations with decreased air conductivity and visual range. By analysing newly-recovered monthly atmospheric electricity data from Kew Observatory, near London, for 1968–1979, averages of the visual range and air conductivity show a close empirical relationship: visual range is reduced when air conductivity is also reduced. The visibility–conductivity correlation is likely to be due to a common modulation of both atmospheric properties by the aerosol number concentration. For the urban air data from Kew, the visual range D and monodisperse aerosol number concentration Z were related by Z D x = A , with x and A found empirically: A is a function of the mean aerosol radius. Through this relationship, local meteorological observations of visual range can provide additional information on aerosol concentration or the electrical properties of air, when no direct measurements are available.
Keywords: Atmospheric electricity; Air pollution; Historical data; Air conductivity;

New Directions: Discussion of “A new generation of ozone critical levels for the protection of vegetation in Europe” by Ashmore et al. by G. Krause; B. Köllner; L. Grünhage; H.-J. Jäger; J. Bender; H.-J. Weigel; M. Ashmore; L. Emberson; P.-E. Karlsson; H. Pleijel (5213-5217).