Atmospheric Environment (v.37, #12)

A case study of aerosol (4.6 nm<D p<10 μm) number and mass size distribution measurements in a busy street canyon in Manchester, UK by I.D. Longley; M.W. Gallagher; J.R. Dorsey; M. Flynn; J.D. Allan; M.R. Alfarra; D. Inglis (1563-1571).
The Air Quality Management community is increasingly turning its attention to urban ‘hot-spots’ where localised high concentrations of pollutants can arise. One such location is the urban street canyon where dispersion is poorly understood or described by regulatory models because of the complexity of the airflow, turbulence and local influences. Similarly, simple metrics such as PM10 fail to describe the range of sizes, composition, sources and behaviours encompassed by the term ‘particle’. A 2-week experimental case study to measure size-segregated aerosol in the size range 4.6 nm–10 μm at a fine time scale (10 min resolution) was undertaken in a typical street canyon in Manchester. The wind direction incident to the canyon, and hence the vortex flow within the canyon, was found to have a large influence on the number concentrations, with values typically 2–10 times greater in perpendicular flow than the estimated inner-urban background. Concentrations were also inversely related to wind speed and directly related to traffic flow. Coarse mode mass concentrations were generally found to follow urban background PM10 concentrations except with a 0–5 μg m−3 enhancement related to traffic-induced re-suspension within the canyon. A small pollution episode consisting of coarse material re-suspended by high winds was extended in time within the canyon.
Keywords: Street canyon; Urban aerosol; Re-suspension; Particle number; Size distribution;

Chemical and radio-chemical composition of freshsnow samples from northern slopes of Himalayas (Cho Oyu range, Tibet) by A Balerna; E Bernieri; M Pecci; S Polesello; C Smiraglia; S Valsecchi (1573-1581).
In September and October 2000, during a scientific and mountaineering expedition (Rome 8000), a continuous series of daily snowfalls have been sampled during the final monsoon and post-monsoon season. The sampling sites were the Gyabrag glacier and the Mt. Cho Oyu west buttress, in the northern slope of the Himalayas range. Samples of freshsnow were collected at different altitudes, ranging from 5700 to 6400 m a.s.l. in the same day and for the same precipitation. Contemporarily, some snow trenches were dug and snow layers were studied and sampled. Conductivity, pH and the major inorganic ions have been analysed with their relative field blanks. The results obtained in the Cho Oyu area have been compared to the ones reported in literature for the southern slopes of the Himalayas range. The comparison shows a substantial homogeneity of main ions concentrations in freshsnow, not depending on the geographical location but only on the monsoon alternation. Freshsnow data showed differences between the monsoon season, with values not substantially influenced by anthropogenic inputs, and the extra-monsoon (post-monsoon, winter and pre-monsoon) season characterised by the influence of dust from central Asia. Some experimental results of in situ radioactivity measurements, obtained with a portable γ-ray detector, are also presented.
Keywords: Himalayas northern slope; Tibet; Freshsnow; Ion chromatography; Radioactivity; Monsoon air masses;

Field measurements were conducted to determine atmospheric concentrations of nitrogen dioxide, nitric acid, formaldehyde, and hydrogen peroxide gases using two dual-channel tunable diode laser absorption systems. These measurements were made as part of the Central California Ozone Study (CCOS) and were conducted for a total of 28 days from July to September 2000 at the Kearney Agricultural Research Station in Parlier, California. All four trace gases exhibit marked diurnal cycles. Ranges of measured concentrations: 1–38 ppb NO2, 0–26 ppb HNO3, 1–17 ppb HCHO, and 0–1.2 ppb H2O2. Formaldehyde, nitric acid and hydrogen peroxide mixing ratios showed unusual behavior during the last intensive measurement period in September 2000.
Keywords: CCOS; Field study; Diurnal profile; Gas phase; Ozone episode;

Aerosol samples were collected in winter at the Mikuni and Mihonoseki sites facing the Sea of Japan and analyzed for non-sea-salt sulfate (nss-SO4 2−), Se(IV) and Se(VI). Episodes of a high nss-SO4 2− concentration were observed 5 times during the observation period of 14 days. Based on the weather conditions as well as the Se/Snss-SO4 2− and Se(VI)/Se(IV) ratios, these episodes could be classified into three types, i.e., continental-coal, local-coal and local-petroleum types. The continental-coal type was characterized by the high Se/Snss-SO4 2− (5.0–7.6×10−4) and high Se(VI)/Se(IV) ratios (6.9–8.9). It was produced by a long-range transport of aerosols originating from coal-combustion sources in the Asian Continent. The local-coal type was due to aerosols from local coal-combustion sources around the observation sites together with high Se/Snss-SO4 2− (3.9×10−4) and low Se(VI)/Se(IV) ratios (0.2). The local-petroleum type was accompanied by low Se/Snss-SO4 2− (2.4×10−4) and low Se(VI)/Se(IV) ratios (3.3) and it was caused by aerosols from local petroleum-combustion sources. The boundary of the Se(VI)/Se(IV) ratio between continental and local types would be around 2.
Keywords: Se(IV); Se(VI); Non-sea-salt sulfate; Atmospheric aerosols; Long-range transport.;

Rainwater composition in northeast Uruguay by M Zunckel; C Saizar; J Zarauz (1601-1611).
The chemical composition of rainfall in northeast Uruguay in 1999 and 2000 and the sources that contribute to the rainwater chemistry are assessed in this study, contributing to a limited knowledge base of rainwater quality in South America. Principal factor analysis and cluster analysis indicate that four main source groups influence the rainfall chemistry over a range of spatial scales. Terrigenous sources (e.g. rock, soil and dust) and agricultural sources (e.g. livestock and crop fertilization) contribute to rainwater chemistry on a local and sub-regional scale. Influx of marine air from the Atlantic Ocean has a regional-scale influence while biomass burning contributes at both a local and sub-regional scale (e.g. fuel wood, and agroindustries) and through long-range transport (forest fires and land clearing). As may be expected in this area dominated by agriculture, the concentrations of ions that are indicative of industrial emissions, NO3 and SO4 2−, are typical of background measurements. The current data are limited, but provide an indication of rain quality and the sources that influence its chemistry in Uruguay. It may be inferred that large-scale biomass burning in the central parts of the continent influence rainwater chemistry on a scale far larger than indicated by the Uruguayan network. Similarly, but to lesser extent, the influx of marine air off the Atlantic Ocean has a greater regional-scale influence than suggested by these data.
Keywords: South America; Rainwater chemistry; Factor analysis; Trajectory analysis; Biomass burning;

Accumulation of atmospheric mercury in forest foliage by J.A. Ericksen; M.S. Gustin; D.E. Schorran; D.W. Johnson; S.E. Lindberg; J.S. Coleman (1613-1622).
We used unique mesocosms to examine the role that plants play in accumulating and transforming atmospheric Hg. Several stands of quaking aspen were grown in large gas-exchange chambers in Hg-enriched soil (12.3±1.3 μg g−1), and the Hg content in the vegetation was determined over time. Foliar Hg concentrations increased as a function of leaf age and leveled off after 2–3 months in the oldest tissue with a mean tissue concentration of 150 ng g−1. Approximately 80% of the total Hg accumulated in the aboveground biomass was found in the leaves, and roughly 1% of that Hg was methylated. Leaves of additional aspen grown within the mesocosms in containers of low Hg soil (0.03±0.01 μg g−1) exhibited foliar Hg concentrations similar to those of trees grown in the Hg-enriched soil. Leaf rinses and surrogate Teflon surfaces were analyzed to characterize surface deposition processes. Small gas-exchange systems were used to measure stomatal uptake of Hg vapor, and the mean Hg flux was −3.3 ng m−2  h−1. These experiments showed that almost all of the Hg in foliar tissue originated from the atmosphere. Thus, in the fall when deciduous trees enter dormancy and leaves senesce, litterfall would represent a new Hg input to terrestrial ecosystems.
Keywords: Plants; Biogeochemistry; Global cycling; Sinks; Uptake;

Seasonal variation of VOC concentrations above a boreal coniferous forest by H Hakola; V Tarvainen; T Laurila; V Hiltunen; H Hellén; P Keronen (1623-1634).
Biogenic volatile organic compound (VOC) concentrations in ambient air were measured in Central Finland from April 2000 to April 2002. The concentrations of isoprene increased in May and declined in September, but the concentrations of its oxidation products, methacrolein and methyl vinyl ketone, remained at about 100 ppt level also after that suggesting they might have anthropogenic sources as well. The winter and summer mean midday concentrations of monoterpenes were 97 and 250 pptv, respectively. The winter concentrations of monoterpenes were unexpectedly high, but they can be explained by small, but existing, emissions from at least Picea abies and also by the much longer atmospheric lifetime of monoterpenes in winter than in summer. The hydroxyl and nitrate radical concentrations in Central Finland were calculated for the year 2000 using an observationally constrained photochemical box model. Using the calculated hydroxyl radical concentrations the atmospheric lifetime of α-pinene with respect to the OH reaction was estimated to be 50 times longer in December than in July. The nitrate and ozone reactions extend the atmospheric lifetime of α-pinene to 3–4 fold in winter in comparison with the summer lifetime.The mean afternoon (12–4 p.m.) emission potentials (at 30°C according to Guenther et al., J. Geophys. Res. 98 (1993) 12609) were 0.4, 0.2, 1.4, 0.7, 0.4, and 0.2 μg g−1 dry weight  h−1 in January, April, May, June, July, and October, respectively. In summer the VOC emissions also included isoprene and sesquiterpenes. The highest isoprene emission potential was observed in June (1.3 μg g−1 dry weight  h−1, (at T=30°C and PPFD=1000 μmol m−2  s−1 according to Guenther et al.) and the highest sesquiterpene emission potential in July (0.6 μg g−1 dry weight  h−1, scaled to 30°C similarly to the monoterpenes).
Keywords: BVOC concentrations; Monoterpene; Isoprene; Sesquiterpene; VOC emission rate; Picea abies; OH radical concentration; NO3 concentration;

Long-term studies on greenhouse gas fluxes during cultivation of energy crops on sandy soils by Hans J Hellebrand; Jürgen Kern; Volkhard Scholz (1635-1644).
The emission of nitrous oxide (N2O) from the soil has a significant impact on the greenhouse gas balance of energy crops. The intensity of nitrogen fertilising affects the source strength of N2O emissions and methane oxidation in the soil. These trace gas fluxes were measured using the flux chamber method in combination with gas chromatography. The mean annually accumulated emission of N2O-N was 1.1 kg N2O-N ha−1  yr−1 ranging from 0.4 to 5.2 kg N2O-N ha−1  yr−1. Sandy soil fertilisation generally led to low N2O-N emissions, ranging from 0.2% to 0.7% of the applied nitrogen. Both, precipitation and temperature significantly influenced the total emission of N2O. The change from dry weather in 1999 to more humid weather in 2000 and 2001 resulted in enhanced N2O emissions. Enhanced N2O emission was also observed due to nitrogen fertilisation, soil cultivation processes and freeze–thaw cycles. Additionally, there were a few comparatively high local N2O emissions with peak values of 900 μg N2O-N m−2  h−1. Methane (CH4) uptake has a clear relationship with soil temperature, having minimum values during the winter and maximum values during the summer. Increasing precipitation significantly reduces the methane uptake by the soil. Non-fertilised plots showed a higher reduction in CH4 uptake due to increasing precipitation than fertilised plots. In sandy soils the mean annually accumulated CH4 uptake varied from 0.36 kg CH4  ha−1  yr−1 (2001) to 0.68 kg CH4  ha−1  yr−1 (1999). With regard to the greenhouse gas balance of energy crops, the low uptake of methane compensates for only 1% of the CO2 equivalent of the N-fertiliser-induced N2O emissions.
Keywords: Nitrous oxide; Fertiliser-induced emission; Emission factor; Methane uptake; Influence of precipitation;

Response of potato to discontinuous exposures of atmospheric ethylene: results of a long-term experiment in open-top chambers and crop growth modelling by Th.A. Dueck; C.J. Van Dijk; C. Grashoff; J. Groenwold; A.H.C.M. Schapendonk; A.E.G. Tonneijck (1645-1654).
A field experiment in open-top chambers (OTCs) was performed to quantitatively assess the growth and yield response of potato to discontinuous exposures to atmospheric ethylene (200, 400 and 800 ppb, applied twice weekly and 200 and 400 ppb applied 4 times weekly, each for 3 h/event). To evaluate the effect of ethylene on potato tuber yield, a module was developed for an existing crop growth simulation model by incorporating the effects of ethylene on epinasty and photosynthesis. Explorations with the model showed that in a worst case scenario, ethylene-induced epinasty had only a marginal effect on tuber yield. Short-term exposures to ethylene under laboratory conditions inhibited photosynthesis, but it recovered within 48 h. When exposed to ethylene for longer than 12 h, irreversible damage of the photosynthesis apparatus occurred.Exposure to ethylene in the OTCs resulted in epinasty and reduced flowering. The number of flowers on potato decreased with increasing concentrations of ethylene, irrespective of the exposure frequency. Calculations showed that the number of flowers was significantly reduced at ca. 170 ppb ethylene, averaged over the hours of exposure. Ethylene concentrations up to 800 ppb, administered 4 times weekly for 3 h during the growing season, did not affect vegetative growth and yield in fumigated potatoes. Under these experimental conditions, the modified simulation model incorporating the effects of ethylene on epinasty and photosynthesis forecasts a 5% effect on tuber yield at concentrations of 1600 ppb. All results indicate that ethylene concentrations higher than 800 ppb are required to adversely affect tuber yield of potato.
Keywords: Solanum tuberosum; Ethylene; Crop growth model; Flowering; Tuber yield;

Wetlands and lowland lakes in the coastal region of North Africa are being lost at an alarming rate as a result of increasing human demands for water and land. Those remaining wetlands, which have not been severely degraded, support high value ecosystems that not only contribute to regional biodiversity but also provide important resources for local human populations. However, information on the current status of these sites and the rates and directions of trends in environmental change over recent decades is generally lacking. In particular, regional data on the inputs of atmospheric pollutants to these important sites are absent. As part of the EU (INCO-MED) funded CASSARINA project, sediment cores were taken from eight coastal lakes in Morocco, Tunisia and Egypt. Chronologies for these cores were produced primarily using radionuclides and all were analysed for spheroidal carbonaceous particles (SCPs). SCPs are produced only from high temperature fossil-fuel combustion and are thus unambiguous indicators of atmospheric deposition from industrial sources. SCP contamination trends appear to show a combination of influences from European and, more recently (post-1980), local North African sources. Contemporary data indicate contamination equivalent to that found in heavily impacted European mountain lakes or moderately impacted lowland lakes in the UK. Such levels of impact raise particular concerns over the future of Moroccan wetland lakes downwind of a recently expanded major coal-fired power station at Jorf Lasar.
Keywords: Atmospheric deposition; Historical record; Industrial pollutants; Lake sediments; Fly-ash particles;

The seasonal isoprene synthase model–biochemical isoprenoid biosynthesis model (SIM–BIM) is a recently developed process-based model to simulate isoprene emissions from vegetation. This model was validated using isoprene emission measurements from adult Quercus petraea (Mattuschka) Liebl. trees growing in a natural forest. Temperature and photosynthetic photon flux density (PPFD) data from a 120-year-old forest stand at Hofstetten in NW Switzerland were used to run SIM–BIM. Experimental isoprene synthase activity and isoprene emission rates from adult Q. petraea trees were compared to the model outputs for the years 2000 and 2001. High correlation (16.5% average deviation for isoprene synthase activity and 28% average deviation for isoprene emission factors) was observed between modelled and experimental data. In addition, a comparison was performed of the modelled values of SIM–BIM to values calculated using the algorithm ISOG97 of Guenther (Ecol. Appl. 7 (1997) 34). On the basis of the temperature and PPFD data from Hofstetten, this comparison clearly displayed the capability of SIM–BIM to simulate dynamic isoprene emission capacities during warm and sunny periods, and thus to model isoprene emission rates in a realistic manner for these conditions.
Keywords: Isoprene emission rate; Seasonality; SIM–BIM; ISOG97; Isoprene synthase; Model validation; Quercus petraea;

Size distributions of mass and chemical components in street-level and rooftop PM1 particles in Helsinki by Tuomo A Pakkanen; Veli-Matti Kerminen; Kati Loukkola; Risto E Hillamo; Päivi Aarnio; Tarja Koskentalo; Willy Maenhaut (1673-1690).
In June 1997, five pairs of simultaneous 24 h atmospheric aerosol samples were collected on working days using Berner low-pressure impactors at 3.5 and 20 m heights at an urban site in Helsinki, Finland. The weather was dry and sunny during the campaign. The results were compared to earlier observations made at the lower site. Average submicron masses were 11 μg/m3 at both heights. Local vehicle exhaust emissions seemed to accumulate particulate mass especially in the 0.15–0.4 μm size range with the average mass concentration being 12% higher at street level for 0.24 μm particles. Long-range transport and sea salt were important for the 0.4–1.3 μm particles leading to slightly higher average mass concentration at the rooftop site for this size-range. Average concentrations of most components, including mass and sulphate, were higher at the rooftop site in the 0.07–0.15 μm size range suggesting that regional or long-range-transported particles and/or local high-level sources might have enhanced these concentrations at the rooftop site. Average submicron concentrations of Cu, Ba, Fe, Sb, Bi, Al and nitrate were higher at street level suggesting that local traffic and road dust were important sources for these components. Concentrations of Ca, Co, Li, Mo, Na, Ni, Pb, Rb, Se, Sr, Ti, Tl, V, MSA, pyruvate, succinate, malonate, SO4 2−, Cl, Na+, K+ and Ca2+ were similar at the two heights or higher at the rooftop site pointing to long-range transport and/or local high-level sources. Comparison of size distributions and concentrations revealed several groups of correlating chemical components: (1) SO4 2−, oxalate, NH4 + and methane sulphonate, (2) Tl, As, K+, Cd, B, glutarate, succinate and Pb, (3) V, Ni, and, to a lesser extent, Co and Mo, (4) Ba, Cu, Fe and Sb, and (5) Zn, Rb, Pb and Mo. The suggested principal sources for the above groups are (1) long-range transport, (2) mainly long-range transport with some local contribution, (3) local oil combustion, (4) vehicle exhaust and brake wear, and (5) various local sources and long-range transport.
Keywords: Particles; Mass; Trace metals; Ions; Size distributions; Vertical distribution;

A Lagrangian stochastic model of dispersion in the atmospheric convective boundary layer is derived. The turbulence is assumed to be non-homogeneous and non-Gaussian in the vertical direction, homogeneous and Gaussian in the horizontal directions. The model describes the evolution of an airborne contaminant in terms of motion of its centroid and diffusion of particles relative to the centroid. The vertical motion of the centroid is simulated using non-stationary Lagrangian stochastic equations incorporating a time-dependent filter for the turbulent energy. The filtering procedure removes the contribution of turbulent eddies smaller than the cloud instantaneous size to the meandering. The instantaneous dispersion of particles relative to the centroid is parameterized using inertial range similarity formulae. The model is applied to the case of continuous stationary releases and the crosswind dispersion is calculated according to Taylor's theory. The model satisfies the well-mixed condition and is capable of calculating all moments of concentration. Mean concentration and concentration fluctuations for several source heights are simulated and compared with laboratory observations.
Keywords: Concentration fluctuations; Air quality models; Particle models; Relative dispersion; Energy filter;

A numerical simulation of annual acid deposition amount in Korea by Jaehee Kim; Boeun Han; SeogYeon Cho (1703-1713).
A comprehensive acid deposition model was used to calculate an annual amount of acid deposition in North East Asia as well as to derive a source–receptor relation. The model results for gaseous SO2 and O3 agree very well with measurements, but the model under-estimated NO2 concentrations. Similarly, the model estimates the sulfate in rain waters quite well but under-estimates nitrate in the rain waters. The correlation coefficients for the spatial distributions of the calculated and measured annual mean concentrations were 0.97, 0.63 and 0.90 for the gaseous SO2, O3, and NO2.One-third of SO2 emitted in North East Asia was calculated to be advected out mostly in the form of sulfate. The amount removed by dry deposition is comparable to that removed by wet deposition for sulfur but it is 40% larger than that by wet deposition for nitrogen. The source–receptor relations derived by the counter-species method show that the wet deposition is more influenced by the long-range transport than the dry deposition. Furthermore, the long-range transport contribution was calculated to be the lowest in the summer and the highest in the winter.
Keywords: Annual acid deposition; Eulerian model; Advection; Source–receptor relation; Counter species;