Atmospheric Environment (v.35, #31)

An atmospheric stability index for the evaluation of urban primary pollution, based on the elaboration of natural radioactivity data yielded by a stability monitor, has been developed. The instrument determines the atmospheric concentration of the short-lived decay products of radon, whose emanation rate can be assumed to be constant in the time and space scale of observation. The index gives information about the dilution properties of the lower boundary layer and allows to highlight the relevant role of the dilution factor in determining primary pollution events.The atmospheric stability indices have been calculated during a 1-yr study carried out in the urban area of Rome (October 1999–September 2000). On the basis of the index, every day of the period has been classified in terms of intensity of a potential primary pollution event. The comparison between this classification and the real concentration value of primary pollutants, measured in the background urban station of Rome, yielded very good results. This shows that the index constitutes a powerful and valuable tool for describing primary pollution events in urban areas and confirms that the role played by the mixing properties of the lower boundary layer is essential in determining primary pollution in urban areas.
Keywords: Radon progeny; Natural radioactivity; Mixing height; Atmospheric boundary layer; Primary pollution;

Saplings of two clones of European white birch (Betula pendula Roth) were exposed to three different ozone profiles resulting in same AOT40 value of 13–14 ppm h in a chamber experiment. The sensitive clone 5 and the more tolerant clone 2 were growing (1) under filtered air (=control), or (2) were exposed to 70 ppb ozone for 24 h d−1 (=profile 1), (3) to 100 ppb ozone for 12 h d−1 at 8:00–20:00 (=profile 2), or (4) to 200 ppb ozone for 4.5 h d−1 at 9:30–14:00 (=profile 3) for 20 d. The saplings were determined for growth, visible leaf injuries, stomatal conductance, and concentrations of Rubisco, chlorophyll and carotenoids. Growth responses and induction of visible foliar injuries under different ozone profiles were variable, resulting in 4–17% lower dry mass of shoot, 16–46% reduction in stem height increment and 11–43% increase in visible injuries in clone 5, which was accompanied by higher leaf turnover rate under profile 3 indicating compensation growth. In clone 2, ozone-induced responses ranged from slight stimulation in stem height growth to 13% decrease in dry mass of shoot and 2–16% increase in visible injuries. Daytime stomatal conductance rates were lowered by 14–54% in clone 5 and 9–74% in clone 2, depending on profile. The additional power-weighted analyses revealed that high peak concentrations and exposure shape were important for induction of visible injuries in both clones and reduction in stomatal conductance in clone 5, whereas growth reductions were rather related to total cumulative exposure. The results indicate that profile of ozone exposure, night-time stomatal conductance (24 h flux), and recovery time for defence and compensations reactions should not be ignored in plant response and ozone flux modelling.
Keywords: Ozone profiles; Exposure indices; Stomatal conductance; Betula pendula Birch; Damage; Chamber experiment; Short-term experiment; Northern European countries;

Ion balances of size-resolved tropospheric aerosol samples: implications for the acidity and atmospheric processing of aerosols by Veli-Matti Kerminen; Risto Hillamo; Kimmo Teinilä; Tuomo Pakkanen; Ivo Allegrini; Roberto Sparapani (5255-5265).
A large set of size-resolved aerosol samples was inspected with regard to their ion balance to shed light on how the aerosol acidity changes with particle size in the lower troposphere and what implications this might have for the atmospheric processing of aerosols. Quite different behaviour between the remote and more polluted environments could be observed. At the remote sites, practically the whole accumulation mode had cation-to-anion ratios clearly below unity, indicating that these particles were quite acidic. The supermicron size range was considerably less acidic and may in some cases have been close to neutral or even alkaline. An interesting feature common to the remote sites was a clear jump in the cation-to-anion ratio when going from the accumulation to the Aitken mode. The most likely reason for this was cloud processing which, via in-cloud sulphate production, makes the smallest accumulation-mode particles more acidic than the non-activated Aitken-mode particles. A direct consequence of the less acidic nature of the Aitken mode is that it can take up semi-volatile, water-soluble gases much easier than the accumulation mode. This feature may have significant implications for atmospheric cloud condensation nuclei production in remote environments. In rural and urban locations, the cation-to-anion ratio was close to unity over most of the accumulation mode, but increased significantly when going to either larger or smaller particle sizes. The high cation-to-anion ratios in the supermicron size range were ascribed to carbonate associated with mineral dust. The ubiquitous presence of carbonate in these particles indicates that they were neutral or alkaline, making them good sites for heterogeneous reactions involving acidic trace gases. The high cation-to-anion ratios in the Aitken mode suggest that these particles contained some water-soluble anions not detected by our chemical analysis. This is worth keeping in mind when investigating the hygroscopic properties or potential health effects of ultrafine particles in polluted environments.
Keywords: Atmospheric aerosol; Inorganic ions; Aerosol chemistry; Gas–particle interactions;

This work presents the computational fluid dynamic modeling of an exhaust plume dispersed from the exhaust pipe of a class-8 tractor truck powered by 330 hp Cummins M11 electronically controlled diesel engine. This effort utilizes an advanced CFD technique to accurately predict the variation of carbon dioxide concentration inside a turbulent plume using a kε eddy dissipation model. The simulation includes the “real-world” operation of a truck and its exhaust plume in a NASA, Langley aircraft testing wind tunnel, that had an effective volume of 226, 535 m3 (8,000,000 ft3). The predicted results show an excellent agreement with the experimentally measured values of CO2 concentrations, dilution ratios, and the temperature variations inside the plume. A specific goal of this effort was to study the effect of recirculation region near the truck walls on dispersion of the plume. For this purpose, growth of the plume from the center of the exhaust pipe is also presented and discussed. This work also shows the benefits of CFD modeling in applications where dispersion correlations are not required a priori, instead the dispersion coefficients are calculated precisely by solving the turbulent kinetic energy and dissipation equations.
Keywords: Plume dispersion; kε turbulent closure; Advection–diffusion transport model; Relative concentration; Dilution ratio;

Sources of fine particle composition in the northeastern US by Xin-Hua Song; Alexandr V. Polissar; Philip K. Hopke (5277-5286).
Fine particle composition data obtained at three sampling sites in the northeastern US were studied using a relatively new type of factor analysis, positive matrix factorization (PMF). The three sites are Washington, DC, Brigantine, NJ and Underhill, VT. The PMF method uses the estimates of the error in the data to provide optimal point-by-point weighting and permits efficient treatment of missing and below detection limit values. It also imposes the non-negativity constraint on the factors. Eight, nine and 11 sources were resolved from the Washington, Brigantine and Underhill data, respectively. The factors were normalized by using aerosol fine mass concentration data through multiple linear regression so that the quantitative source contributions for each resolved factor were obtained. Among the sources resolved at the three sites, six are common. These six sources exhibit not only similar chemical compositions, but also similar seasonal variations at all three sites. They are secondary sulfate with a high concentration of S and strong seasonal variation trend peaking in summer time; coal combustion with the presence of S and Se and its seasonal variation peaking in winter time; oil combustion characterized by Ni and V; soil represented by Al, Ca, Fe, K, Si and Ti; incinerator with the presence of Pb and Zn; sea salt with the high concentrations of Na and S. Among the other sources, nitrate (dominated by NO3 ) and motor vehicle (with high concentrations of organic carbon (OC) and elemental carbon (EC), and with the presence of some soil dust components) were obtained for the Washington data, while the three additional sources for the Brigantine data were nitrate, motor vehicle and wood smoke (OC, EC, K). At the Underhill site, five other sources were resolved. They are wood smoke, Canadian Mn, Canadian Cu smelter, Canadian Ni smelter, and another salt source with high concentrations of Cl and Na. A nitrate source similar to that found at the other sites could not be obtained at Underhill since NO3 was not measured at this site. Generally, most of the sources at the three sites showed similar chemical composition profiles and seasonal variation patterns. The study indicated that PMF was a powerful factor analysis method to extract sources from the ambient aerosol concentration data.
Keywords: Receptor modeling; Positive matrix factorization (PMF); Source identification; Northeastern US;

Variability-lifetime relationship of VOCs observed at the Sonnblick Observatory 1999—estimation of HO-densities by Thomas Karl; Paul J. Crutzen; Michael Mandl; Michael Staudinger; Alex Guenther; Alfons Jordan; Ray Fall; Werner Lindinger (5287-5300).
An extensive dataset of VOC measurements was collected at the Sonnblick Observatory, Austria (3106 m) in Fall/Winter 1999/2000, showing high mixing ratios of anthropogenic and biogenic VOCs at this high altitude site due to upward mixing of air masses (Geophys. Res. Lett. 2F (2001) 507). Here we give an interpretation of proton-transfer-reaction (PTR-MS) mass scans obtained in November 1999 based on fragmentation data, GC-PTR-MS analysis and the variability-lifetime relationship, described by the power law, σ(ln(x))= b . The variability-lifetime plot of anthropogenic VOCs gave a proportionality factor A of 1.40 and a,b exponent (sink term) of 0.44 and allowed an estimate of average HO-densities on the order of (1.5±0.4)×105  molecules cm−3. Additionally we were able to indirectly determine a diurnal HO-profile with peak values of (1.3±0.5)×106  molecules cm−3 around midday. HO-reaction rate coefficients for higher aldehydes (heptanal to nonanal) were estimated due to photochemical losses during a stagnant air episode (27 November) and from the variability-lifetime relationship. Combining long term PTR-MS analysis of VOCs and the variability-lifetime method provides a valuable tool for assessing the dominant cause of the variability in VOC concentrations. This information is essential in understanding the sources and photochemical processing of VOCs detected in ambient air at field measurement sites.

Laboratory and field investigations of a new and simple design for the parallel plate denuder by Kai Rosman; Masahiko Shimmo; Anders Karlsson; Hans-Christen Hansson; Petri Keronen; Andrew Allen; Gerd Hoenninger (5301-5310).
Diffusion denuders are commonly used for collection of water soluble atmospheric gases. Denuder plates made of glass with silica coating were however difficult to handle in field measurements, and also had wettability problems. In this paper, we describe a new design of parallel plate denuder consisting of perfluoralkoxy (PFA) plates and polyester sheets. The parallel plate denuder was coupled on-line to ion chromatography for analysis of atmospheric HNO3 and SO2. With time resolution of 20 min, the detection limits for both gases were 6 ppt(v). Memory effect was found to be significant for HNO3 especially at high humidity with the long sample inlet tube. Particle losses due to diffusion and electrostatic effects in the denuder were investigated and compared with theory. Particle loss in the sample inlet tube was found to play an important role by reducing the number of charged particles entering the denuder. The instrument was applied in two European Union field measurement campaigns, and the intercomparison results are presented in this paper.
Keywords: Atmospheric gases; Nitric acid; Sulfur dioxide; Particle loss; Field measurements;

The history of methyl chloroform emissions: 1951–2000 by A McCulloch; P.M Midgley (5311-5319).
A complete record of annual methyl chloroform production has been compiled by combining early estimates in the technical literature (1951–1976) with audited production data supplied by chemical manufacturers (1970–1996) and with production and consumption estimates provided by the countries party to the Montreal Protocol (1989 to the present). From this, a new and comprehensive estimate of annual emissions has been developed. However, when the atmospheric concentrations calculated from these annual emissions are compared with measured concentrations, there are significant discrepancies, particularly during recent years, that merit further examination.
Keywords: Atmospheric concentration; 1,1,1-trichloroethane;

Coarse atmospheric aerosol: size distributions of trace elements by K. Eleftheriadis; I. Colbeck (5321-5330).
A sampler, employing nine single stage impactors placed in parallel within a portable wind tunnel, has been used to determine the metal content of coarse atmospheric aerosol. The wind tunnel maintains a constant flow environment for the collectors housed inside it, so that representative sampling conditions are achieved compared to the varied ambient wind conditions. At a flow rate of 8 m s−1 the 50% cut-off diameters of the impactors ranged from 7.8 to 38.8 μm. Measurements were conducted at a rural and urban site near Colchester in south east England. The samplers were analysed by PIXE for P, K, Ca, Fe, Ti, Mn, Cu, V, Co, Cr, Br, Zn, Ni, Sc and Pb. It is found that the sampler can be employed to quantitatively characterise the elemental mass size distribution for aerosol larger than 10 μm. The results indicate that a small fraction of the above earth and trace elements’ metal mass is present in particles greater than 10 μm. This fraction for earth metals (Ca, K, Ti) is comparatively greater in the rural site than the urban site, while for trace metals (Mn, V, Cu, Cr) this fraction constitutes a more significant part of the coarse mass at the urban site. Trace element concentrations were of a similar order of magnitude to earlier literature reports. Although the number of measurements was limited it can be concluded that the size distributions obtained were characteristic of an unpolluted area.
Keywords: Coarse aerosol; Trace elements; Tunnel sampler; Single stage impactor; Size distribution;

Gaseous emissions from outdoor concrete yards used by livestock by T.H Misselbrook; J Webb; D.R Chadwick; S Ellis; B.F Pain (5331-5338).
Measurements of ammonia (NH3), nitrous oxide (N2O) and methane (CH4) were made from 11 outdoor concrete yards used by livestock. Measurements of NH3 emission were made using the equilibrium concentration technique while closed chambers were used to measure N2O and CH4 emissions. Outdoor yards used by livestock proved to be an important source of NH3 emission. Greatest emission rates were measured from dairy cow feeding yards, with a mean of 690 mg NH3-N m−2  h−1. Smaller emission rates were measured from sheep handling areas, dairy cow collecting yards, beef feeding yards and a pig loading area, with respective mean emission rates of 440, 280, 220 and 140 mg NH3-N m−2  h−1. Emission rates of N2O and CH4 were much smaller and for CH4, in particular, emission rates were influenced greatly by the presence or absence of dung on the measurement area.
Keywords: Ammonia emission; Nitrous oxide; Methane; Concrete yards;

HNO3 analyzer by scrubber difference and the NO–ozone chemiluminescence method by Masatoshi Yamamoto; Motonori Tamaki; Hiroshi Bandow; Yasuaki Maeda (5339-5346).
A fast response analyzer for HNO3 in highly polluted air is described. The time resolution attainable was 12 s. The method is based on the difference in a technique for HNO3-scrubbed and non-scrubbed air and the reduction of HNO3 to NO with the use of a line of catalytic converters and a method for the subsequent NO-ozone chemiluminescence. A sample air stream, in which particulates are removed with a Teflon filter, is divided into two channels. CH-1 is directly connected to the converter line, and CH-2 contains a HNO3 scrubber packed with a nylon fiber that goes to another converter line. Each converter line is composed of a hot quartz-bead converter (QBC) and a molybdenum converter (MC) in a series. A QBC reduces HNO3 to (NO+NO2), which is called NO x . The MC reduces the NO x to NO.For CH-1, the analyzer detects most compounds that typically comprise NO y (J. Geophys. Res. 91 (1986) 9781). These CH-1 compounds are called NO y ′ hereafter (NO y -particulate nitrate) because the particulates are removed by the filter. A difference in the detector signal for the two channels indicates HNO3. For a blank test, atmospheric air in which HNO3 was pre-scrubbed by an extra nylon fiber was introduced to the analyzer. Variations in the blank value were 0.38±0.42 and 0.34±0.55 ppb during the high readings (NO y ′-HNO3 ) (called NO y * hereafter) (111±12 ppb, N=180), and low NO y * readings (62±8 ppb, N=180), respectively, indicating that the lowest detection limit of the analyzer is 1.1 ppb (2σ). When the data obtained with the analyzer is compared to the data using the denuder method, a linear correlation with the regression of Y=0.973X+0.077 (r 2=0.916 (N=20)) in the range of 0–6.5 ppb HNO3 is obtained, which is an excellent agreement. Atmospheric monitoring was carried out at Kobe. Although the average concentration of HNO3 was 2.6±1.3 ppb, ca.10 ppb for a HNO3 concentration was occasionally observed when the NO y * concentration was high, i.e., more than 100 ppb.
Keywords: Fast response HNO3 analyzer; Quartz-bead converter; Molybdenum converter; Nylon filter; NO y ;

Analysis of time-series data sets, collected in vernacular buildings and workplaces linked with radium source bedrock has identified a number of internal and external pressure characteristics linking meteorological parameters with the variability of radon gas and its progeny. The cellars in these buildings are excavated from the bedrock associated with the radium source and have relatively high levels of radon concentration along with largely stable microclimatic conditions, which differ from those of the buildings’ ground and upper levels. In workplace environments cyclical characteristics are apparent, associated with heating and ventilation related to working hours. Comparative radon concentration data, collected within buildings and similarities identified between buildings, suggest the need to distinguish between short and longer-term influences. From a range of comparative data studied, water vapour pressure, a partial pressure of barometric pressure, is indicated as a principal determinant of the short-term variability of radon gas concentrations, with barometric pressure determining the trend or general longer term level, both linked to temperature. Wind speed appears to have the potential for a dual influence on radon variability: directly, through wind pressure differences and indirectly, through changes to the water vapour component.
Keywords: Radon/weather linkage; Advective-flow; Pressure-variables;

NO x and NO2 concentrations were measured at different locations in a city centre of an urban zone (Population 450 000) in order to study the variation of the outdoor exposure at pedestrian level. These measurements were carried out to understand the influence of traffic emissions at each measured site. The observations were done during four weeks in winter, including several days with high pollution levels. The results at different locations have been used to analyse criteria recommended for locating observation sites in a monitoring network. No large differences in background pollution averaged over several weeks have been found throughout the city centre, even during pollution peaks. Measurements were also carried out inside one street canyon. The contribution of the street traffic to the NO=NO x −NO2 concentrations observed at side-walk has been found important, i.e., several times the background level. On the other hand, the majority of observed NO2 pollution is due to the contribution of background pollution within the street. The pollutant excess at pedestrian level is strongly correlated to the street traffic emission and to the atmospheric turbulence observed at roof level. Application of a box model to the street data demonstrates that such models can be useful to estimate the pollutant accumulation within the street.
Keywords: NO x ; Traffic emission; Urban pollution; Street canyon;

Sampling and chemical analysis of ice crystals as a function of size by S.H. Ehrman; M. Schwikowski; U. Baltensperger; H.W. Gäggeler (5371-5376).
Size-classified ice crystal samples were collected during the Spring of 1998, at the Jungfraujoch High-Alpine Research Station (3454 m), located in Switzerland. A procedure modified from the Guttalgor method, originally developed for size-selective sampling of raindrops by Bächmann et al. (Atmos. Environ. 26A (1992) 1795) was used to sample ice crystals during precipitation events. The size-classified ice crystal samples were analyzed using ion chromatography to determine the concentrations of Na+, NH4 +, K+, Ca2+, Mg2+, Cl, NO3 , and SO4 2− in each size class. For ions associated with coarse mode aerosol, Na+, K+, Ca2+, Mg2+, and Cl, concentration increased with decreasing ice crystal size, suggesting scavenging by nucleation. For the remaining ions, mixed behavior was observed suggesting a combination of gas phase scavenging and scavenging via riming.
Keywords: Aerosol scavenging; Aerosol particles; Guttalgor; Ice crystals; Size dependence;