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Atmospheric Environment (v.39, #26)

Editorial board (pp. i).

List for forthcoming papers (pp. i-ii).

Large-scale changes in the cloud radiative forcing over the Indian region by S.D. Patil; R.K. Yadav (pp. 4609-4618).

Based on earth radiation budget experiment (ERBE) data, earlier studies have shown that in tropical deep-convective regions there is a near cancellation between shortwave and longwave cloud radiative forcing and El Nino event affects the cloud radiative forcing in the Pacific Ocean. The present study investigates these features over the Indian region (0–30°N, 60–120°E) in the peak monsoon month July, (being a representative month of the southwest monsoon season) using satellite measurements of ERBE and International Satellite Cloud Climatology Project (ISCCP) cloud data during the period 1985–1989. It has been observed from the study that a unique imbalance is seen between shortwave cloud radiative forcing (SWCRF) and longwave cloud radiative forcing (LWCRF). It is found to be prominent when the magnitude of LWCRF is higher than 50Wm⁻². Net cloud radiative forcing (NCRF) is highly negative in the Indian region from Arabian sea to Indochina and near zero in the equatorial Indian Ocean. The ratio N, i.e.,N=-SWCRF/LWCRF, is showing significantly higher values for all the years, the variation of observed N against SWCRF also shows higher values with SWCRF during average of 1985–1989, 1987 and 1988 because it is more than(N=∼1) that mentioned by Kiehl and Ramanathan (1990, Comparison of cloud forcing derived from the earth radiation budget experiment with that simulated by NCAR community climate model. Journal of Geophysical Research 95, 11679–11698) suggesting more imbalance between SWCRF and LWCRF and the lowering of the cloud top pressure particularly in 1987. Cloud radiative forcing (CRF) components are undergoing year-to-year variability with maximum magnitude in 1988 and minimum in 1987 similar to rainfall variation over the region, indicating an association between monsoon rainfall activity and CRF. Large-scale reduction occurred in the magnitudes of CRF and cloud physical properties in the Arabian Sea and south Bay of Bengal especially in 1987, and NCEP/NCAR-vertical velocity for 700hPa is also found considerably weak in 1987 in the Arabian Sea and Bay of Bengal i.e., the reduction in the vertical velocity might have affected the cloud formation and their vertical growth and ultimately changed the CRF. We attribute this reduction to the anomalous subsidence associated with the 1987 El Nino event.

Keywords: Radiative balance; Monsoon rainfall activity; E1 Nino event; Near cancellation

Surface air radon progeny at S�o Jos� dos Campos, Brazil by A.A. Silva; L.H. Claro (pp. 4619-4625).

Radon is a noble gas naturally occurring in the atmosphere with its progeny. Such progeny can be divided into short- and long-lived daughters. In the winter and spring of 2004 a field campaign at São José dos Campos (SJC, 23.1° S, 45.5° W, 600m above sea level) in Brazil was conducted to determine the outdoor concentration of the short-lived²¹⁸Po,²¹⁴Pb, and²¹⁴Bi and the long-lived²¹⁰Po. It was adopted the methodology of measuring the integrated counts of alpha particles from atmospheric aerosols captured on a cellulose membrane filter sampled with outdoor surface air. Integrated counts for the short-lived daughters at 3 different minute-based periods of time were carried out immediately after the end of sampling and applied to a system of 3 equations, whose solution is the short-lived daughters’ air concentrations. For²¹⁰Po the air concentration was directly released from alpha counts and volume of probed air. Radionuclides’ uncertainties were calculated too. Average values of volume activity (25±21) (1 standard deviation, sd), (6±4), and (4±2)Bqm⁻³ for²¹⁸Po,²¹⁴Pb, and²¹⁴Bi, respectively, and (81±30)μBqm⁻³ for²¹⁰Po were found in the campaign. Atmospheric parameters of temperature, humidity, precipitation, pressure, and wind were taken during sampling. Correlation with temperature and humidity were obtained at 95% confidence level.

Keywords: Radon progeny; Aerosols; Natural radioactivity

Properties of aerosols from sugar-cane burning emissions in Southeastern Brazil by L.L. Lara; P. Artaxo; L.A. Martinelli; P.B. Camargo; R.L. Victoria; E.S.B. Ferraz (pp. 4627-4637).

The influences of biomass burning emissions in the composition of aerosol have been studied during 1 year around the city of Piracicaba (Southeastern Brazil). Inhalable particles, separated in PM_2.5 and coarse particulate mode (CPM, with size in the range (2.5< d_p<10μm)), were sampled from April 1997 to March 1998 and analyzed for BC, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Se, Br, Rb, Sr, Zr, Pb. The average concentrations of PM_2.5, CPM, BC and chemical elements were statistically higher in the dry season than in the wet season. The results of absolute principal component analysis showed four and three different sources for PM_2.5 and CPM, respectively. Sugar-cane burning is the main source of PM_2.5 representing 60% of PM_2.5, soil dust accounted for 14%, and industries and oil combustion contributed with 12% each one. Resuspended soil is the main source of CPM followed by industrial emissions and sugar-cane burning. The sampling and analytical procedures applied in this study showed that sugar-cane burning and agricultural practices are the main sources of inhalable particles, possibly altering the aerosol composition around the city of Piracicaba.

Keywords: Aerosol composition; Biomass burning; Black carbon; Aerosol source apportionment; Brazil

A study of volatile organic compounds evolved in urban waste disposal bins by M. Statheropoulos; A. Agapiou; G. Pallis (pp. 4639-4645).

Volatile organic compounds (VOCs) evolved in urban waste disposal bins in different situations were studied. Waste of various loads (full, empty, partially filled bins), remained uncollected in the containers for variable time and under different weather conditions. Analysis of VOCs was carried out by thermal desorption/gas chromatography/mass spectrometry (TD/GC/MS). Over 150 compounds have been identified and the 30 most abundant were quantified. Generally, VOCs were determined in the range of micrograms per cubic meter. Median concentrations of the most prominent VOCs were: decane (694.9μgm⁻³), acetic acid ethyl ester (353.1μgm⁻³), limonene (334.9μgm⁻³), nonane (257.4μgm⁻³), ethanol (216.1μgm⁻³), benzene 1,2,4-trimethyl (212.6μgm⁻³) and undecane (159.1μgm⁻³). High levels of alkanes, alkylbenzenes and terpenes are responsible for undesirable odours. The variety and concentration of VOCs evolved depends on the prevailing conditions such as time of waste exposure, load and weather. When waste accumulates in bins under unforeseen circumstances, some compounds produced may exceed olfactory and safety thresholds representing a source of potential health impact.

Keywords: Volatile organic compounds (VOCs); Waste bins; Household; Garbage; Odour

Flow field measurements in the proximity of an urban intersection in London, UK by A. Dobre; S.J. Arnold; R.J. Smalley; J.W.D. Boddy; J.F. Barlow; A.S. Tomlin; S.E. Belcher (pp. 4647-4657).

Observations were made using a roof-top automatic weather station and four ultrasonic anemometers deployed in the proximity of an intersection in London, UK, during the 4-week DAPPLE project field campaign in spring 2003. At the intersection, the measurements show that the wind direction can switch between the different streets, suggesting that intersections are potent mechanisms for dispersion. Despite the complexity of the building geometry in the vicinity of the intersection, measurements in the adjoining streets indicate that the main large-scale features are along-street channelling and an across-street recirculating vortex, similar to those observed in idealised two-dimensional street canyons. Analysis over a relatively broad range of roof-top wind directions demonstrates that flow within the streets is the vector sum of a channelling and a recirculation vortex. Furthermore, channelling depends linearly on the along-street component of the roof-top reference wind, whilst the cross-street recirculation vortex depends linearly on the component of the roof-top reference wind perpendicular to the street. The results demonstrate that these simple ideas are robust enough to occur in streets of non-ideal geometry and are established a short distance from an intersection.

Keywords: Urban meteorology; Street canyon; Street flows; Ultrasonic anemometry; DAPPLE

Impact of ship emissions on the Mediterranean summertime pollution and climate: A regional model study by Elina Marmer; B�erbel Langmann (pp. 4659-4669).

Ship emissions contribute substantially to atmospheric pollution over the summertime Mediterranean region, thereby modifying the radiation budget through sulfate aerosol forcing. By applying a regional atmospheric-chemistry model and a radiation model we determine the seasonal variability of secondary trace gases and aerosols, their origin and impact on climate. Summer mean sulfate aerosol column burden over the Mediterranean is 7.8mgm⁻² and remarkably higher than the European mean of 4.7mgm⁻². Partitioning SO _x emissions into land and water sources allows to investigate their respective impact on the sulfate aerosol concentration, its total burden and direct radiative forcing. 54% of the total sulfate aerosol column burden over the Mediterranean in summer originates from ship emissions. Accordingly, they contribute over 50% to the direct radiative forcing. Running the model without ship emissions significantly reduces near surface concentration of sulfate, ozone, nitric acid, hydroxy radicals and formaldehyde. As the applied ship emission inventory is based on the year 1990 and model results tend to underestimate observed concentrations at Mediterranean locations influenced by ship emissions, we assume that increased ship emissions during the past decade contribute nowadays even stronger to secondary pollution formation and radiative forcing.

Keywords: Regional modeling; Sulfate forcing; Ship emissions; Mediterranean Sea

Atmospheric dry deposition in the vicinity of the Salton Sea, California—I: Air pollution and deposition in a desert environment by R. Alonso; A. Bytnerowicz; W.I. Boarman (pp. 4671-4679).

Air pollutant concentrations and atmospheric dry deposition were monitored seasonally at the Salton Sea, southern California. Measurements of ozone (O₃), nitric acid vapor (HNO₃), ammonia (NH₃), nitric oxide (NO), nitrogen dioxide (NO₂) and sulfur dioxide (SO₂) were performed using passive samplers. Deposition rates of NO₃⁻, NH₄⁺, Cl⁻, SO₄²⁻, Na⁺, K⁺ and Ca²⁺ to creosote bush branches and nylon filters as surrogate surfaces were determined for one-week long exposure periods. Maximum O₃ values were recorded in spring with 24-h average values of 108.8μgm⁻³. Concentrations of NO and NO₂ were low and within ranges of the non-urban areas in California (0.4–5.6 and 3.3–16.2μgm⁻³ ranges, respectively). Concentrations of HNO₃ (2.0–6.7μgm⁻³) and NH₃ (6.4–15.7μgm⁻³) were elevated and above the levels typical for remote locations in California. Deposition rates of Cl⁻,SO42–, Na⁺, K⁺ and Ca²⁺ were related to the influence of sea spray or to suspended soil particles, and no strong enrichments caused by ions originated by human activities were detected. Dry deposition rates ofNO3– andNH4+ were similar to values registered in areas where symptoms of nitrogen saturation and changes in species composition have been described. Deposition of nitrogenous compounds might be contributing to eutrophication processes at the Salton Sea.

Keywords: Ozone; Nitrogenous pollutants; Major ions; Surrogate surfaces; Arid ecosystems

Atmospheric dry deposition in the vicinity of the Salton Sea, California—II: Measurement and effects of an enhanced evaporation system by R. Alonso; A. Bytnerowicz; J.L. Yee; W.I. Boarman (pp. 4681-4689).

A study was conducted to determine the effects of salt spray drift from pilot technologies employed by the US Bureau of Reclamation on deposition rates of various air-born ions. An enhanced evaporation system (EES) was tested in the field at the Salton Sea, California. Dry deposition ofNO3–,NH4+,SO42–, Cl⁻, Ca²⁺, Na⁺, K⁺ and Se was assessed by using nylon filters and branches of natural vegetation exposed for one-week long periods. The simultaneous exposure of both lyophilized branches and branches of live plants offered important information highlighting the dynamics of deposited ions on vegetation. The EES significantly increased the deposition rates of Cl⁻,SO42– and Na⁺ in an area of about 639–1062m surrounding the sprayers. Similarly, higher deposition of Ca²⁺ and K⁺ caused by the EES was detected only when deposition was assessed using nylon filters or lyophilized branches. Deposition fluxes ofNO3–,NH4+ and Se were not affected by the spraying system. Techniques for measuring dry deposition and calculating landscape-level depositional loads in non-forested systems need further development.

Keywords: Surrogate surfaces; Leaf surfaces; Arid ecosystems; Major ions

Linear fuzzy-discriminant analysis applied to forecast ozone concentration classes in sea-breeze regime by Cristian Ghiaus (pp. 4691-4702).

A discriminant analysis model using 1-day lagged ozone maximum concentration and the weather forecast of wind and temperature proves to correctly classify ozone episodes, if reasonable error ranges are accepted. Seven classes are defined around the ozone level of interest, each having a range of about 7.5–10% of the absolute value of the class. This paper introduces the fuzzyness of the class boundaries which result in predictions that may belong to more classes. Since the maximal accepted measurement error is ±10%, misclassification in one class up or down is acceptable; a measure of correct forecast probability is also provided. The model typically misses one event out of 10 and gives about two false alarms per year, for periods and locations different from the training set. The tests have been conducted for 3 years using forecast skill parameters designed for rare event forecast; the probability of detection is about 98% and the Heidke score is around 80%.

Keywords: Ground-level ozone; Statistical modeling; Environmental warning system

Comparison of a road traffic emission model (HBEFA) with emissions derived from measurements in the Gubrist road tunnel, Switzerland by Christina A. Colberg; Bruno Tona; Werner A. Stahel; Markus Meier; Johannes Staehelin (pp. 4703-4714).

Road vehicle emissions contribute significantly to air pollution. These traffic emissions are characterized by emission factors (EFs), which describe the emitted mass of a compound per driven distance. Here, we present a comparison of EFs which were obtained with two different techniques: (i) Trace gas measurements in the Gubrist tunnel, Switzerland in fall 2002 (Colberg et al., 2005. Atmospheric Environment, in press) provided real-world EFs of entire vehicle fleets and, after statistical regression analysis, additionally the EFs of different vehicle classes. Furthermore, a 12 year time series of EFs of measurements in the Gubrist tunnel in Switzerland is being used (Steinemann und Zumsteg, 2003, Bericht US 89-16-11 f�r OSTLUFT durch Amt f�r Abfall, Wasser, Energie und Luft des Kantons Z�rich (AWEL), Switzerland). (ii) Based on dynamometric test measurements and engine maps at different conditions, EFs of single vehicles are combined with a comprehensive road traffic emission model (HBEFA, 1999. Umweltbundesamt Berlin, Bundesamt f�r Umwelt, Wald und Landschaft Bern (published as software on CD-ROM), Infras AG, Bern; HBEFA, 2004. Umweltbundesamt Berlin, Umweltbundesamt Wien, Bundesamt f�r Umwelt, Wald und Landschaft Bern (published as software on CD-ROM), Infras AG, Bern).The results of both techniques are processed and if enough information on the vehicle fleet is available, a comparable standard is achieved, which allows the validation of the road traffic emission model. Since two HBEFA versions are being used the improvement of the model can be shown nicely. The results demonstrate good agreement for the trends of the time series measurements. However, a deviation for the absolute EFs of NO _x is observed for light- and heavy-duty vehicles (LDV and HDV, respectively). The HBEFA, 2004 derived estimates are larger than 50% for LDV and 15% for HDV compared to the EF derived from the tunnel study. The deviation is even more prominent for the CO emissions (75% overestimation for LDV and 130% overestimation for HDV). The VOC emissions could only be compared for LDV. There the deviation is within the confidence interval of the measurements. The strengths and weaknesses of both techniques are revealed by this study.

Keywords: Road traffic emissions; Real-world emissions; Emission models; Emission factors; Real-world emissions; Validation of emission models; Controlled converters.

Characterisation of TSP and PM2.5 at Iza�a and Sta. Cruz de Tenerife (Canary Islands, Spain) during a Saharan Dust Episode (July 2002) by A. Andr�s Alastuey; Xavier Querol; Sonia Castillo; Miguel Escudero; Anna Avila; Emilio Cuevas; Carlos Torres; P.-M. Pedro-Miguel Romero; Francisco Exposito; Garcia Omaira Garc�a; J. Pedro Diaz; Rita Van Dingenen; Jean P. Putaud (pp. 4715-4728).

A strong African dust outbreak episode affecting the Canary Islands from 28 to 31/07/02 has been characterised at the Izaña Observatory (IZO), located in the free troposphere (FT), and at Sta. Cruz de Tenerife (SCO), in the Marine Boundary Layer (MBL). The Saharan air mass intruded above the trade wind inversion layer resulting in daily mean PM levels of up to 616, 312, 98 and 26μgm⁻³ of TSP, PM10, PM2.5 and PM1, respectively, at IZO. As demonstrated by the vertical sounding profiles, the MBL is compressed during the Saharan intrusion, favouring the deposition of coarse dust particles to the MBL and giving rise to daily levels of up to 85, 52 and 30μgm⁻³ of PM10, PM2.5 and PM1, respectively, at SCO.A complete chemical and mineralogical characterisation has been performed for TSP and PM2.5 collected simultaneously at both sites. Levels of mineral elements increased during the Saharan episode at both sampling sites. In addition, at the MBL, the levels of the secondary inorganic aerosols registered during the Saharan episode were considerably higher than levels recorded during non-Saharan episodes. The partial formation of secondary coarse Ca and/or Na sulphates and nitrates by the reaction of gaseous pollutants (or derived oxidised phases), of a major local origin, with the natural aerosols has been deduced. These reactions may be favoured by the high concentration of coarse mineral and marine aerosols particles measured at SCO, the high relative humidity (RH) measured, as well as the strong compression of the MBL during the Saharan episode.

Keywords: Mineral dust; Secondary aerosols; Free troposphere; Marine boundary layer; Air quality

Dispersion within a model urban area by Jing Yuan; Akula Venkatram (pp. 4729-4743).

This paper analyzes the data collected in a field study conducted in Dugway Proving Ground, Utah, from 17 to 26 July 2001. The experiment was designed to simulate a source in an urban area modeled at a scale of roughly 1:10. The model urban canopy was constructed with 55-gallon drums laid out in a 5 by 9 array. Propylene (C₃H₆), the tracer, was released and sampled at 3 receptor arcs both within the barrel array and over flat terrain. Turbulence, velocity, and temperature were measured with sonic anemometers. A comparison of observations made with and without the obstacle array indicated that the obstacle array significantly increased lateral and vertical dispersion. The arc maximum surface concentrations observed within the array were well explained by a dispersion model based on that of Van Ulden [1978. Atmospheric Environment 12, 2125–2129] and modified by Venkatram [2004. Atmospheric Environment 38, 1337–1344] to use on-site measurements of mean wind and turbulence. The major conclusion of this study is that estimating dispersion within the urban canopy requires flow information below the canopy top.

Keywords: Dispersion; Obstacle array; Model urban area; Field experiment; Tracer study; Plume spread; Dispersion model; Data analysis

Radioactive contamination of atmospheric dust over southeastern New Mexico by Richard Arimoto; Joel L. Webb; Marsha Conley (pp. 4745-4754).

Aerosol particle samples were collected at three sites located near the Waste Isolation Pilot Plant (WIPP), a deep underground nuclear waste-storage facility, and they were analyzed to investigate the spatial and temporal variations in the concentrations of selected radionuclides and inorganic substances. The activities of²³⁸Pu,^239,²⁴⁰Pu,²⁴¹Pu and²⁴¹Am were determined by alpha spectrometry following a series of chemical separations, and the concentrations of Al, U and Th were determined in a separate set of samples by inductively-coupled plasma mass spectrometry. There was no evidence for impacts of the WIPP on radionuclide activity concentrations. Rather, the activities of both naturally-occurring (U and Th) and man-made (²⁴¹Am and^239,240Pu) radionuclides in the aerosols peaked in spring and tracked the loadings of Al, an indicator of mineral dust. More than half of the variability in the^239,240Pu at the sampling site closest to the WIPP could be explained by the seasonal cycles of atmospheric dust. For U and Th, the predictive value of Al was even higher: 66% to over 90% of the variance in these nuclides could be explained by their relationship to dust. Extrapolation of the data to a global scale suggests that ∼0.02% of the total^239,240Pu from nuclear weapons’ fallout currently recirculates between the earth and atmosphere each year. In terms of monitoring releases from nuclear facilities, the results presented here demonstrate that elemental data provide information directly relevant to understanding causes for variability in the activities of atmospheric radionuclides.

Keywords: Dust; Aerosol particles; Radionuclides; Resuspension

Direct emission factor for N₂O from rice–winter wheat rotation systems in southeast China by Jianwen Zou; Yao Huang; Yanyu Lu; Xunhua Zheng; Yuesi Wang (pp. 4755-4765).

A field experiment was conducted in a rice–winter wheat rotation agroecosystem to quantify the direct emission of N₂O for synthetic N fertilizer and crop residue application in the 2002–2003 annual cycle. There was an increase in N₂O emission accompanying synthetic N fertilizer application. Fertilizer-induced emission factor for N₂O (FIE) averaged 1.08% for the rice season, 1.49% for the winter wheat season and 1.26% for the whole annual rotation cycle. The annual background emission of N₂O totaled 4.81kg N₂O–Nha⁻¹, consisting of 1.24kg N₂O–Nha⁻¹ for rice, 3.11kg N₂O–Nha⁻¹ for wheat seasons. When crop residue and synthetic N fertilizer were both applied in the fields, crop residue-induced emission factor for N₂O (RIE) was estimated as well. When crop residue was retained at the rate of 2.25 and 4.50tha⁻¹ for each season, the RIE averaged 0.64% and 0.27% for the whole annual rotation cycle, respectively. Based on available multi-year data of N₂O emissions over the whole rice–wheat rotation cycle at 3 sites in southeast China, the FIE averaged 1.02% for the rice season, 1.65% for the wheat season. On the whole annual cycle, the FIE for N₂O ranged from 1.05% to 1.45%, with an average of 1.25%. Annual background emission of N₂O averaged 4.25kgha⁻¹, ranging from 3.62 to 4.87kgha⁻¹. It is estimated that annual N₂O emission in paddy rice-based agroecosystem amounts to 169Gg N₂O–N in China, accounting for 26–60% of the reported estimates of total emission from croplands in China.

Keywords: N; ₂; O; Emission factor; Background emission; Fertilizer; Crop residue

Cloud condensation nucleus activity of internally mixed ammonium sulfate/organic acid aerosol particles by J.P.D. Abbatt; K. Broekhuizen; P. Pradeep Kumar (pp. 4767-4778).

The ability of mixed ammonium sulfate/organic acid particles to act as cloud condensation nuclei (CCN) has been studied in the laboratory using a continuous flow, thermal-gradient diffusion chamber operated at supersaturations between 0.3% and 0.6%. The organic acids studied were malonic acid, azelaic acid, hexanoic acid, cis-pinonic acid, oleic acid and stearic acid, and the particles were largely prepared by condensation of the organic vapor onto a dry ammonium sulfate core. For malonic acid and hexanoic acid, the mixed particles activated as predicted by a simple K�hler theory model where both species are assumed to be fully soluble and the droplet has the surface tension of water. Three low-solubility species, cis-pinonic acid, azelaic acid and oleic acid, are well modeled where the acid was assumed to be either partially or fully insoluble. Interestingly, although thin coats of stearic acid behaved in a manner similar to that displayed by oleic and cis-pinonic acid, we observed that thick coats led to a complete deactivation of the ammonium sulfate, presumably because the water vapor could not diffuse through the solid stearic acid. We observed no CCN behavior that could be clearly attributed to a lowering of the surface tension of the growing droplet by the presence of the organic constituents, some of which are highly surface active.

Keywords: Cloud condensation nuclei; Organic aerosols; Cloud activation; Kohler theory

Observational study of ozone and carbon monoxide at the summit of mount Tai (1534m a.s.l.) in central-eastern China by Jian Gao; Tao Wang; Aijun Ding; Chunbo Liu (pp. 4779-4791).

We report measurement results of ozone (O₃) and carbon monoxide (CO) obtained from 5 July to 23 November 2003 at the summit of Mount Tai (1534m a.s.l, 36.25°N, 117.10°E) in the Shandong Peninsula of China. The study was carried out to gain insights into regional O₃ pollution and air-mass transport in the highly populated North China (Huabei) Plains. The average mixing ratio was 58 (±16) ppbv for O₃ and 393 (±223) ppbv for CO during the study period. The monthly variations in O₃ and CO exhibited a similar pattern, i.e. high in summer and low in autumn. While such a seasonal pattern for O₃ is a common phenomenon in many rural areas in the Northern Hemisphere and is mainly due to seasonal changes in solar radiation and temperature, the higher CO levels in summer were attributed to the difference in dynamic transport and the evolution of PBL heights in summer and autumn over this region. An examination of diurnal variations in O₃ indicated evident daytime photochemical production, especially in summer. The evolution of PBL heights and mountain-valley breezes also had a large impact on the diurnal patterns of O₃ and CO. O₃ and CO showed a moderately good positive correlation (r=0.60) in July with a slope of 0.08ppbv/ppbv, which is much lower than the slope (0.3–0.4ppbv/ppbv) observed in North America. A back trajectory analysis showed that air masses mainly originated from the North China Plains or were re-circulating over the Shandong Peninsula, collectively accounting for 76% of the air masses sampled. Summertime air traveling in the lower troposphere over northern China had the highest concentrations of O₃ and CO, revealing that the lower troposphere in northern China was significantly polluted in summer due to strong convection transporting PBL pollution to the free troposphere. The trajectories also showed notable contributions from eastern China, central China, and countries in northeast Asia such as Korea and Japan.

Keywords: Tropospheric O; ₃; Northern China; Photochemical production; Long-range transport; Back trajectory analysis

Evidence of an increasing NO₂/NO _X emissions ratio from road traffic emissions by David C. Carslaw (pp. 4793-4802).

A statistical analysis of roadside concentrations of nitrogen oxides (NO _X) and nitrogen dioxide (NO₂) in London shows that from 1997 to 2003 there has been a statistically significant downward trend (at thep=0.004 level) in NO _X averaged across a network of 36 sites. Conversely, there has been no statistically significant trend in the concentrations of NO₂ over the same period. Hourly modelling using a simple constrained chemical model shows that the NO₂/NO _X emissions ratio from road traffic has increased markedly from a mean of about 5–6vol% in 1997 to about 17vol% in 2003. Calculations show that if the NO₂/NO _X emissions ratio had remained the same as that towards the beginning of each time series, 14 out of the 36 sites would have shown a statistically significant downward trend in NO₂ at thep=0.10 level compared with only five that did. The increase in the NO₂/NO _X emissions ratio from road traffic in recent years has therefore had a significant effect on recent trends in roadside NO₂ concentrations. It is shown that the increased use of certain types of diesel particulate filters fitted to buses is likely to have made an important contribution to the increasing trends in the NO₂/NO _X emissions ratio. However, it is unlikely that these filters account for all of the observed increase and other effects could be important, such as the increased penetration of diesel cars in the passenger car fleet and new light- and heavy-duty engine technologies and management approaches.

Keywords: Primary NO; ₂; Nitrogen dioxide; Diesel particulate filter; Trend analysis; Mann–Kendall; London; Urban air quality

Photochemistry of reduced sulfur compounds in a landfill environment by Zang-Ho Shon; Ki-Hyun Kim; Eui-Chan Jeon; Min-Young Kim; Yoo-Keun Kim; Sang-Keun Song (pp. 4803-4814).

This study examines the distribution characteristics of reduced sulfur compounds (RSCs such as DMS, CS₂, H₂S, DMDS, and CH₃SH) and their photochemical reactions in landfill air. The photochemical conversions of RSCs to a further oxidized form, SO₂ were evaluated in the landfill site using a photochemical box model. Measurements of RSCs were carried out from landfill areas in Daegu, Korea, during a wintertime period (e.g., 13–16 Jan 2004). This study indicated that H₂S was the most dominant RSC in the landfill, with the concentrations of 4.2±5.8ppbv. The chemical species of RSCs, which may exert influences on the SO₂ production depending on sampling conditions, were found to include DMS, DMDS, and H₂S. In general, the RSC contribution to the observed SO₂ levels was insignificant in the sampling sites investigated. Overall, the extent of the RSC oxidation to the observed SO₂ varied dramatically during the sampling period. The photochemical conversion of the RSCs in the landfill environment can account for about 15% of the observed SO₂, on average. There was a strong correlation between DMS and SO₂ concentration levels during the study period.

Keywords: RSCs; H; ₂; S; SO; ₂; Landfill; Daegu

New Directions: Improved atmosphere in pubs due to the smoking ban in Ireland by Aonghus McNabola; Brian Broderick; Paul Johnston; Laurence Gill (pp. 4815-4816).

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Atmospheric Environment (v.39, #26)