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Atmospheric Environment (v.44, #19)

Editorial board (pp. i).

Exposure to particulate matter in traffic: A comparison of cyclists and car passengers by Luc Int Panis; Bas de Geus; Grégory Vandenbulcke; Hanny Willems; Bart Degraeuwe; Nico Bleux; Vinit Mishra; Isabelle Thomas; Romain Meeusen (pp. 2263-2270).

Emerging evidence suggests that short episodes of high exposure to air pollution occur while commuting. These events can result in potentially adverse health effects. We present a quantification of the exposure of car passengers and cyclists to particulate matter (PM). We have simultaneously measured concentrations (PNC, PM2.5 and PM10) and ventilatory parameters (minute ventilation (VE), breathing frequency and tidal volume) in three Belgian locations (Brussels, Louvain-la-Neuve and Mol) for 55 persons (38 male and 17 female). Subjects were first driven by car and then cycled along identical routes in a pairwise design. Concentrations and lung deposition of PNC and PM mass were compared between biking trips and car trips.Mean bicycle/car ratios for PNC and PM are close to 1 and rarely significant. The size and magnitude of the differences in concentrations depend on the location which confirms similar inconsistencies reported in literature. On the other hand, the results from this study demonstrate that bicycle/car differences for inhaled quantities and lung deposited dose are large and consistent across locations. These differences are caused by increased VE in cyclists which significantly increases their exposure to traffic exhaust. The VE while riding a bicycle is 4.3 times higher compared to car passengers. This aspect has been ignored or severely underestimated in previous studies. Integrated health risk evaluations of transport modes or cycling policies should therefore use exposure estimates rather than concentrations.

Keywords: Personal exposure; Traffic emissions; Air pollution inhalation; Cycling; Active travel; Physical activity; UFP; PNC; Ultrafine particulate matter; Lung deposited dose

Seasonal and diurnal measurements of carbon monoxide and nonmethane hydrocarbons at Mt. Wilson, California: Indirect evidence of atomic Cl in the Los Angeles basin by Katrine A. Gorham; Nicola J. Blake; Richard A. VanCuren; Henry E. Fuelberg; Simone Meinardi; Donald R. Blake (pp. 2271-2279).

We present a study of the seasonal and diurnal variability of carbon monoxide and selected volatile organic compounds in the Los Angeles area. Measurements were made during four different nine-day field campaigns in April/May, September, and November, 2007, and February, 2008, at the Mt. Wilson sampling site, which is located at an elevation of approximately 1700 m in the San Gabriel Mountains overlooking Pasadena and the Los Angeles basin. The results were used to characterize the Mt. Wilson site as a representative location for monitoring integrated Los Angeles basin emissions, and, by reference to carbon monoxide emissions, to estimate average annual emissions. The considerable seasonal variability of many hydrocarbons, in both their measured mixing ratios and their relationship to carbon monoxide, was indicative of variable source strengths. Most interestingly, perturbation of C₄ hydrocarbon ratios suggested an enhanced role for chlorine chemistry during the month of September, likely as the result of Los Angeles’ coastal location. Such coastal influence was confirmed by observations of enhanced mixing ratios of marine halocarbons, as well as air mass back trajectories.

Keywords: Nonmethane hydrocarbons; VOCs; Carbon monoxide; Mt. Wilson; Los Angeles basin; Urban pollution; Marine boundary layer Cl chemistry

Experimental evidence of biomass burning as a source of atmospheric¹³⁷Cs, puy de Dôme (1465 m a.s.l.), France by L. Bourcier; K. Sellegri; O. Masson; R. Zangrando; C. Barbante; A. Gambaro; J.-M. Pichon; J. Boulon; P. Laj (pp. 2280-2286).

The presence of cesium-137 (¹³⁷Cs) in the environment is mainly due to past nuclear tests and accidental reactor releases. Due to the half-life of¹³⁷Cs (30.2 y), amounts of this radionuclide releases are in fact still detectable in soils, and at trace levels in the vegetation and the atmosphere. Since the middle of the 1990’s, the presence of¹³⁷Cs in the atmosphere has long been attributed to the resuspension of terrestrial dust. Recently, modelling studies have demonstrated that an additional and possibly dominant source of this anthropogenic radionuclide is biomass burning. Here, we report the variations of atmospheric¹³⁷Cs activity levels over a 2-year period at the puy de Dôme (1465 m a.s.l.), France in combination with measurements of the aerosol chemical composition, in particular with indicators for biomass burning (levoglucosan and potassium) and soil dust (calcium). Temporal co-variations of these chemical compounds in addition to back-trajectories are used to identify common source emissions. Significant correlation is found between these compounds. Hence, we experimentally confirm the modelling study highlighting the fact that the atmospheric¹³⁷Cs is partly released by biomass burning. In addition, we observed that the correlations between the¹³⁷Cs concentrations and levoglucosan and biomass burning K⁺ differ according to the season. This is in agreement with the temporal evolution of levoglucosan concentration, which has maxima in winter and minima in summer.

Keywords: Cesium; Levoglucosan; Biomass burning; Resuspension

Source identification of particulate matter collected at underground subway stations in Seoul, Korea using quantitative single-particle analysis by Hae-Jin Jung; BoWha Kim; JiYeon Ryu; Shila Maskey; Jo-Chun Kim; Jongryeul Sohn; Chul-Un Ro (pp. 2287-2293).

Subway particle samples collected at four underground subway stations in Seoul, Korea were characterized by a single-particle analytical technique, low- Z particle electron probe X-ray microanalysis. To clearly identify indoor sources of subway particles, four sets of samples collected in tunnels, at platforms, near ticket offices, and outdoors were investigated. For the samples collected in tunnels, Fe-containing particles predominate, with relative abundances of 75–91% for the four stations. The amounts of Fe-containing particles decrease as the distance of sampling locations from the tunnel increases. In addition, samples collected at the platform in subway stations with platform screen doors (PSDs) that limit air-mixing between the platform and the tunnel showed marked decreases in relative abundances of Fe-containing particles, clearly indicating that Fe-containing subway particles are generated in the tunnel. PM₁₀ mass concentration levels are the highest in the tunnels, becoming lower as the distance of sampling locations from the tunnel increases. The extent of the decrease in PM₁₀ in stations with PSDs is also larger than that in stations without PSDs. The results clearly indicate that Fe-containing particles originating in tunnels predominate in the indoor microenvironment of subway stations, resulting in high indoor PM₁₀ levels, and that PSDs play a significant role in reducing Fe-containing particles at platforms and near ticket offices.

Keywords: Subway particles; Single particle analysis; Low-; Z; particle electron probe X-ray microanalysis; Aerosol analysis

Phthalate and PAH concentrations in dust collected from Danish homes and daycare centers by Sarka Langer; Charles J. Weschler; Andreas Fischer; Gabriel Bekö; Jørn Toftum; Geo Clausen (pp. 2294-2301).

As part of the Danish Indoor Environment and Children’s Health (IECH) study, dust samples were collected from 500 bedrooms and 151 daycare centers of children (ages 3 to 5) living on the island of Fyn. The present paper reports results from the analyses of these samples for five phthalate esters (diethyl phthalate (DEP), di(n-butyl) phthalate (DnBP), di(isobutyl) phthalate (DiBP), butyl benzyl phthalate (BBzP), di(2-ethylhexyl) phthalate (DEHP)) and three PAHs (pyrene, benz[a]anthracene (B[a]A) and benzo[a]pyrene (B[a]P)). The three PAHs and DEHP were detected in dust samples from all sites, while DEP, DnBP, DiBP and BBzP were detected in more than 75% of the bedrooms and more than 90% of the daycare centers. The dust mass-fractions of both phthalates and PAHs were log-normally distributed. With the exception of DEP, the mass-fractions of phthalates in dust were higher in daycare centers than homes; PAH mass-fractions in dust were similar in the two locations. There was no correlation among the different phthalates in either homes or daycare centers. In contrast, the PAH were correlated with one another – more strongly so in homes ( R²=0.80–0.90) than in daycare centers ( R²=0.28–0.45). The dust levels of several phthalates (BBzP, DnBP and DEHP) were substantially lower than those measured in a comparable study conducted 6–7 years earlier in Sweden. Although usage patterns in Denmark differ from those in Sweden, the current results may also reflect a change in the plasticizers that are used in common products including toys. PAH levels were roughly an order of magnitude lower than those measured in Berlin and Cape Cod residences, suggesting that the Danish sites are less impacted by motor vehicle emissions.

Keywords: Indoor environment; Settled dust; Phthalates; PAH; Homes; Daycare centers

Five years of formaldehyde and acetaldehyde monitoring in the Rio de Janeiro downtown area – Brazil by Sergio Machado Corrêa; Graciela Arbilla; Eduardo Monteiro Martins; Simone Lorena Quitério; Claudinei de Souza Guimarães; Luciana Vanni Gatti (pp. 2302-2308).

The fuel matrix used in Brazil is unique around the world. The intensive use of hydrated ethanol, gasohol (gasoline with 25% v/v of ethanol), compressed natural gas (CNG), and biodiesel leads to a peculiar composition of the urban atmosphere. From 1998 to 2002 an increase in formaldehyde levels was observed and since then, a reduction. This work presents a monitoring campaign that was executed from March 2004 to February 2009 by sampling at early morning on every sunny Wednesday for a total of 183 samples. The results indicate a strong reduction in formaldehyde levels from 2004 (average of 135.8μgm⁻³ with SD 28.4μgm⁻³) to 2009 (average of 49.3μgm⁻³ with SD 27.4μgm⁻³). The levels of acetaldehyde showed a slight reduction from 2004 (average of 34.9μgm⁻³ with SD 8.0μgm⁻³) to 2009 (average of 26.8μgm⁻³ with SD 11.5μgm⁻³). Comparing the results with the concurrent evolution of the fleet and of fuel composition indicates that the observed formaldehyde levels could be associated with the increase in ethanol use and in CNG use by engines with improved technology over the first converted CNG engines. Modelling studies using the OZIPR trajectory model and the SAPRC chemical mechanism indicate that formaldehyde is the main ozone precursor in Rio de Janeiro and acetaldehyde is the forth one.

Keywords: Formaldehyde; Acetaldehyde; Modelling; Vehicular emissions; Incremental reactivity

Monthly variations in nitrogen isotopes of ammonium and nitrate in wet deposition at Guangzhou, south China by Guodong Jia; Fajin Chen (pp. 2309-2315).

Monthly nitrogen isotopes of ammonium and nitrate in wet deposition in the city of Guangzhou, and the causes of their variability, are reported in this paper. Nitrate δ¹⁵N showed nearly constant values around zero in the dry season (October to April), but oscillating values from negative to positive in the rainy season (May to September). By contrast, ammonium δ¹⁵N displayed lower values during the rainy season than in the dry season. The rural area north of the city was considered as the prominent source of ammonium and nitrate in spring and early summer (May and June), as suggested by their concurrent negative isotopic trends and higher NH₄⁺/NO₃⁻ ratios. From July to September, different dominating sources from the city, i.e., fossil fuel combustion for nitrate, and sewage and waste emission for ammonium, caused disparate δ¹⁵N trends of the two species, showing positive nitrate δ¹⁵N, but still negative ammonium δ¹⁵N. During the cool dry season, the high values of ammonium δ¹⁵N and concurrently low NH₄⁺/NO₃⁻ ratios suggested the decrease in NH₃ volatilization and relatively important thermogenic origin of ammonium, but the intermediate nitrate δ¹⁵N values around zero may be a result of a balanced emission of NO_x from the city and the rural areas. The isotopic effects of chemical conversion of NO_x to nitrate and washout of nitrate were ruled out as significant causes of nitrate δ¹⁵N variability, but ammonium washout, during which¹⁵N is assumed to be preferentially removed, may partly contribute to the ammonium δ¹⁵N variability.

Keywords: Nitrogen isotope; Ammonium; Nitrate; Rainwater; South China

Evaluation of aerosol sources at European high altitude background sites with trajectory statistical methods by Pedro Salvador; Begoña Artíñano; Casimiro Pio; Joana Afonso; Michel Legrand; Hans Puxbaum; Samuel Hammer (pp. 2316-2329).

This study has investigated the influence of synoptic weather patterns and long-range transport episodes on the concentrations of several compounds related to different aerosol sources (EC, OC, SO₄²⁻, Ca²⁺, Na⁺, K⁺,²¹⁰Pb, levoglucosan and dicarboxylic acids) registered in PM10 or PM2.5 aerosol samples collected at three remote background sites in central Europe. Air mass back-trajectories arriving at these sites have been analysed by statistical methods. Firstly, air mass back-trajectories have been grouped into clusters. Each cluster corresponds to specific meteorological scenarios, which were extracted and discussed. Finally, redistributed concentration fields have been computed to identify the main potential source regions of the different key aerosol components. A marked seasonal pattern is observed in the occurrence of the different clusters, with fast westerly and northerly Atlantic flows during winter and weak circulation flows in summer. Spring and fall were characterised by advection of moderate flows from northeastern and eastern Europe. Significant inter-cluster differences were observed for concentrations of receptor aerosol components, with the highest concentrations of EC, OC, SO₄²⁻, K⁺ and²¹⁰Pb associated with local and mesoscale aerosol sources located over central Europe related to enhanced photochemical processes. Emissions produced by fossil fuel and biomass burning processes from the Baltic countries, Byelorussia, western regions of Russia and Kazakhstan in spring and fall also contribute to elevated levels of EC, OC, SO₄²⁻, K⁺ and²¹⁰Pb. In the summer period long-range transport episodes of mineral dust from North-African deserts were also frequently detected, which caused elevated concentrations of coarse Ca²⁺ at sites. The baseline aerosol concentrations in central Europe at the high altitude background sites were registered in winter, with the exception of coarse Na⁺. While the relatively high concentrations of Na⁺ can be explained by sea salt advected from the Atlantic, the low levels of other aerosol components are caused by efficient aerosol scavenging associated to advections of Atlantic air masses, as well as lower emissions of these species over the Atlantic compared to those over the European continent and very limited vertical air mass exchange over the continent.

Keywords: Trajectory statistical methods; Cluster analysis; Redistributed concentration field method; Geochemistry; Long-range transport; PM10; PM2.5

PM10 emission factors for non-exhaust particles generated by road traffic in an urban street canyon and along a freeway in Switzerland by N. Bukowiecki; P. Lienemann; M. Hill; M. Furger; A. Richard; F. Amato; A.S.H. Prévôt; U. Baltensperger; B. Buchmann; R. Gehrig (pp. 2330-2340).

Recent studies have shown clear contributions of non-exhaust emissions to the traffic related PM10 load of the ambient air. These emissions consist of particles produced by abrasion from brakes, road wear, tire wear, as well as vehicle induced resuspension of deposited road dust. The main scope of the presented work was to identify and quantify the non-exhaust fraction of traffic related PM10 for two roadside locations in Switzerland with different traffic regimes. The two investigated locations, an urban street canyon with heavily congested traffic and an interurban freeway, are considered as being typical for Central Europe. Mass-relevant contributions from abrasion particles and resuspended road dust mainly originated from particles in the size range 1–10 μm. The results showed a major influence of vehicle induced resuspension of road dust. In the street canyon, the traffic related PM10 emissions (LDV: 24 ± 8 mg km⁻¹ vehicle⁻¹, HDV: 498 ± 86 mg km⁻¹ vehicle⁻¹) were assigned to 21% brake wear, 38% resuspended road dust and 41% exhaust emissions. Along the freeway (LDV: 50 ± 13 mg km⁻¹ vehicle⁻¹, HDV: 288 ± 72 mg km⁻¹ vehicle⁻¹), respective contributions were 3% brake wear, 56% resuspended road dust and 41% exhaust emissions. There was no indication for relevant contributions from tire wear and abrasion from undamaged pavements.

Keywords: Emission factors; Abrasion; PM10; Brake wear; Resuspension

Conversion of nitrogen oxides on commercial photocatalytic dispersion paints by S. Laufs; G. Burgeth; W. Duttlinger; R. Kurtenbach; M. Maban; C. Thomas; P. Wiesen; J. Kleffmann (pp. 2341-2349).

In the present study, photocatalytic reactions of nitrogen oxides (NO_x = NO + NO₂) were studied on commercial TiO₂ doped facade paints in a flow tube photoreactor under simulated atmospheric conditions. Fast photocatalytic conversion of NO and NO₂ was observed only for the photocatalytic paints and not for non-catalytic reference paints. Nitrous acid (HONO) was formed in the dark on all paints studied, however, it efficiently decomposes under irradiation only on the photocatalytic samples. Thus, it is concluded that photocatalytic paint surfaces do not represent a daytime source of HONO, in contrast to other recent studies on pure TiO₂ surfaces. As main final product, the formation of adsorbed nitric acid/nitrate anion (HNO₃/NO₃⁻) was observed with near to unity yield. In addition, traces of H₂O₂ were observed in the gas phase only in the presence of O₂. Formation of the greenhouse gas nitrous oxide (N₂O) could be excluded. The uptake kinetics of NO, NO₂ and HONO was very fast under atmospheric conditions (e.g. γ(NO + TiO₂) > 10⁻⁵). Thus, the uptake on urban surfaces (painted houses, etc.) will be limited by transport. For a hypothetically painted street canyon, an average reduction of nitrogen oxide levels of ca. 5% is estimated. Since the harmful HNO₃/NO₃⁻ is formed on the surface of the photoactive paints, whereas it is formed in the gas phase in the atmosphere, the use of photocatalytic paints may also help to reduce acid deposition, e.g. on plants, or nitric acid related health issues.

Keywords: Nitrogen oxides; Nitrous acid; Nitric acid; Photocatalysis; TiO; ₂

Study on dissolved organic carbon in precipitation in Northern China by Yuepeng Pan; Yuesi Wang; Jinyuan Xin; Guiqian Tang; Tao Song; Yinghong Wang; Xingru Li; Fangkun Wu (pp. 2350-2357).

Dissolved organic carbon (DOC) was measured in 483 precipitation samples collected at 10 sites in Northern China from December 2007 to November 2008. The annual volume-weighted mean (VWM) concentrations and wet deposition fluxes of DOC for 10 sites ranged from 2.4 to 3.9 mg C/L and 1.4 to 2.7 g C m⁻² yr⁻¹, respectively. The proportion of DOC to total organic carbon (TOC) was 79% on average, suggesting that a significant fraction of TOC was present as insoluble particulate organic carbon. Due to intensive domestic coal use for house heating and smaller dilution of scavenged organic carbon, higher VWM concentrations of DOC were observed during winter and spring than during summer and autumn. When precipitation events were classified via air mass back-trajectories, the mixed trajectories from SE and NW always corresponded to significantly higher DOC than those from SE or NW alone, coinciding with the centre of a low pressure system moved eastward and the wind direction changed from southeast to northwest. The results also showed that each site had a similar seasonal variation for DOC wet deposition flux. The largest flux occurred during the rainy season, and the lowest flux appeared during winter months. The product of the TC/DOC ratio and the DOC flux yielded an average TC wet deposition flux of 3.2 g C m⁻² yr⁻¹ in Northern China, accounting for 8.6% and 22% of the carbon sink magnitude (37 g C m⁻² yr⁻¹) in terrestrial ecosystems and anthropogenic carbon emissions (14 g C m⁻² yr⁻¹), respectively. This indicates that atmospheric wet deposition of TC is a significant carbon flux that cannot be neglected in regional models of the carbon cycle, and should be considered along with dry deposition in the removal mechanism for carbon from regional atmosphere.

Keywords: DOC; Wet deposition flux; Rainwater carbon composition; Regional carbon cycle; Northern China

Illicit psychotropic substance contents in the air of Italy by Angelo Cecinato; Catia Balducci; Valentina Budetta; Antonello Pasini (pp. 2358-2363).

Two in-field campaigns were performed in 2009 to elucidate the contents of illicit psychotropic substances in airborne particulates of Italian cities. Twenty-eight localities of eight Italian regions were investigated in winter, and further eleven sites in June (14 regions in total), thanks to contribution of Regional Environmental Agencies. Cocaine was found almost everywhere, although some sites were rural or suburban. The maximum was recorded in Milan in winter (∼0.39 ng m⁻³), and “high” values (up to ∼0.16 ng m⁻³) in other Northern cities and in Rome. Besides cocaine, three cannabinoids will be monitored, namely Δ⁹-tetrahydrocannabinol, cannabidiol and cannabinol. The three compounds often affected the air at lower extents than cocaine, and sometimes resulted absent. Cannabinol accounted for up to 90% of the total. The concentrations of illicit compounds were up to six times lower in June than in winter. This decrease was probably induced by the lowering of boundary layer height typical of winter, and by the oxidizing capacity of atmosphere, which is stronger in the warm season. Compared to n-alkanes, polynuclear aromatic compounds, nicotine, caffeine and airborne particulate, cocaine seemed to follow a peculiar behaviour; in fact, meaningful (≥0.80) Pearson (linear) regression coefficients were calculated from the corresponding concentrations only at local scale (e.g. Rome), and within just one season. Improvements of the method are needed to monitor illicit drug metabolites (e.g. benzoylecgonine, ecgonine methyl ester, 9-carboxy-11-nor-Δ⁹-tetrahydrocannabinol), heroin and semi-volatile amphetamines.

Keywords: Psychotropic substances; Cocaine; Cannabinoids; Airborne particulate; Atmospheric pollution

Elemental carbon and sulfate aerosols over a rural mountain site in the northeastern United States: Regional emissions and implications for climate change by A.J. Khan; Jianjun Li; Vincent A. Dutkiewicz; Liaquat Husain (pp. 2364-2371).

The effect of elemental carbon (EC) on global as well as regional climate forcing is potentially very important. However, the EC data for northeastern U.S. is sparse. Daily EC concentrations, [EC], and [SO₄] were measured in the northeastern U.S. at a regionally representative rural site, Whiteface Mountain (WFM; 44.366°N, 73.903°W, 1.5 km amsl, above mean sea level), New York (NY), for 1997. The air mass origin was determined using 6-h backward in time air trajectories obtained from the Hybrid Single-Particle Lagrangian Integrated Trajectory Model (HYSPLIT 4). [EC] and [SO₄] were highly variable and influenced by synoptic–scale meteorology (rainy vs dry periods). The maximum daily [EC] and [SO₄] were 364 ± 55 and 28,800 ± 3000 ng m⁻³, respectively. [EC] and [SO₄] also showed seasonal variations at WFM. Occurrences of high daily [EC] were mainly in spring months, while peak daily [SO₄] concentrations occurred in summer months. This behavior of aerosols is due to the fact that the sources of EC and SO₄ are not the same and also due to the enhanced photochemical activity during summer months that increased the production of SO₄ from SO₂. High [EC] and [SO₄] values were associated with westerly air flow from the industrialized Midwestern U.S. Sector analysis using HYSPLIT 4 air trajectories showed that regions lying between the southwest and northwest of the WFM contributed 81% and 83% of the [EC] and [SO₄], respectively. The monthly net direct radiative forcing for shortwave (SW) due to EC and SO₄ aerosols at the top of the atmosphere (TOA) varied from −0.05 to −0.50 W m⁻², with an annual average of −0.20 ± 0.15 W m⁻² that gives a net cooling effect. Average net radiative forcing at WFM for clear sky is lower than the global average radiative forcing reported by IPCC ().

Keywords: Elemental carbon; Black carbon; Sulfate; Radiative forcing; Whiteface Mountain

Natural emissions for regional modeling of background ozone and particulate matter and impacts on emissions control strategies by Bonyoung Koo; Chao-Jung Chien; Gail Tonnesen; Ralph Morris; Jeremiah Johnson; Tanarit Sakulyanontvittaya; Piti Piyachaturawat; Greg Yarwood (pp. 2372-2382).

Natural emissions adopted in current regional air quality modeling are updated to better describe natural background ozone and PM concentrations for North America. The revised natural emissions include organosulfur from the ocean, NO from lightning, sea salt, biogenic secondary organic aerosol (SOA) precursors, and pre-industrial levels of background methane. The model algorithm for SOA formation was also revised. Natural background ozone concentrations increase by up to 4ppb in annual average over the southeastern US and Gulf of Mexico due to added NO from lightning while the revised biogenic emissions produced less ozone in the central and western US. Natural PM_2.5 concentrations generally increased with the revised natural emissions. Future year (2018) simulations were conducted for several anthropogenic emission reduction scenarios to assess the impact of the revised natural emissions on anthropogenic emission control strategies. Overall, the revised natural emissions did not significantly alter the ozone responses to the emissions reductions in 2018. With revised natural emissions, ozone concentrations were slightly less sensitive to reducing NOx in the southeastern US than with the current natural emissions due to higher NO from lightning. The revised natural emissions have little impact on modeled PM_2.5 responses to anthropogenic emission reductions. However, there are substantial uncertainties in current representations of natural sources in air quality models and we recommend that further study is needed to refine these representations.

Keywords: Background ozone; Background PM; _2.5; Natural source; Air quality modeling; Control strategy

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Atmospheric Environment (v.44, #19)