Atmospheric Environment (v.156, #C)

Large eddy simulation is performed for the dispersion of a passive scalar in the turbulent boundary layer over an urban-like roughness surface under neutral and stable stratification. Square arrays of cubical obstacles are used to model the urban canopy with a ground level point source located in front of the obstacle. We design cases for varying building intervals to investigate the relationship between flow patterns and dispersion processes for different plan area densities λ p . It has been found (Shen et al. 2015) that flow patterns in a three-dimensional urban canopy can be classified into five basic regimes in neutral stratification: isolated roughness, external wake interference, internal wake interference, skimming flow and streets network. This classification still holds in the presence of moderately stable stratification. In area with large λ p , the material released from the point source tends to be trapped by the leeward recirculation and is well-mixed inside the canopy. The mean concentration level within roughness canopies is high due to the reduced advection velocity. In area with small λ p , the great part of the material is entrained into the horseshoe vortex wrapping around the obstacle and carried downwind. The material is concentrated in the lower region of the canopy with a relatively higher temporal fluctuation. In the presence of stable stratification, the spread of the plume is reduced and the temporal fluctuation is suppressed as well. For area of large λ p , the advective part of the scalar flux is responsible for carrying the material at ground level aloft into the urban canopy layer.
Keywords: Urban dispersion; Stable stratification; Large eddy simulation; Flow pattern;

Origins and trends in ethane and propane in the United Kingdom from 1993 to 2012 by R.G. Derwent; R.A. Field; P. Dumitrean; T.P. Murrells; S.P. Telling (15-23).
Continuous, high frequency in situ observations of ethane and propane began in the United Kingdom in 1993 and have continued through to the present day at a range of kerbside, urban background and rural locations. Whilst other monitored C2 – C8 hydrocarbons have shown dramatic declines in concentrations by close to or over an order of magnitude, ethane and propane levels have remained at or close to their 1993 values. Urban ethane sources appear to be dominated by natural gas leakage. Background levels of ethane associated with long range transport are rising. However, natural gas leakage is not the sole source of urban propane. Oil and gas operations lead to elevated propane levels in urban centres when important refinery operations are located nearby. Weekend versus weekday average diurnal curves for ethane and propane at an urban background site in London show the importance of natural gas leakage for both ethane and propane, and road traffic sources for propane. The road traffic source of propane was tentatively identified as arising from petrol-engined motor vehicle refuelling and showed a strong downwards trend at the long-running urban background and rural sites. The natural gas leakage source of ethane and propane in the observations exhibits an upwards trend whereas that in the UK emission inventory trends downwards. Also, inventory emissions for natural gas leakage appeared to be significantly underestimated compared with the observations. In addition, the observed ethane to propane ratio found here for natural gas leakage strongly disagreed with the inventory ratio.
Keywords: Ethane; Propane; Natural gas leakage; NMVOC inventories;

Composition and mixing states of brown haze particle over the Himalayas along two transboundary south-north transects by Zhiwen Dong; Shichang Kang; Junming Guo; Qianggong Zhang; Xuejia Wang; Dahe Qin (24-35).
Pollutants that are usually transported from southern Asia to the Tibetan Plateau deposit on the Plateau surface, change snow albedo and thereby surface radiative flux. This results numerous climatic implications like as erratic monsoon, perturbation in hydrological cycle, etc. However, the accurate estimation of these climatic implications is not well understood, because the atmospheric pollution is a heterogeneous mixture of various particle types. Therefore, this part of climate research requires a detailed investigation of physical and chemical properties of atmospheric pollutants. This study aimed to examine the physical and chemical properties of atmospheric pollutants across the Himalayan regions along two transboundary south-north transects. The information of individual-particles was obtained using microscopy-based techniques that comprises transmission electron microscope (TEM) and Energy-dispersive X-ray spectrometer (EDX). Study capture the signatures of various types of atmospheric species such as black carbon (BC), mineral dust, fly ash, organic matter, sulfate, nitrite, ammonium, and NaCl. Microscopy-based techniques confirm that these particles were generally in mixing state, for example salt-coated particles accounting for 25–56% of the total particles in sampled locations. Our analysis shows that urban and rural locations are characterized with atmospheric particles which sourced from anthropogenic activities, whereas remote locations with those released from natural crustal. However, the relative contributions of anthropogenic particles were higher than that of particles released from natural crustal. The presence of such particles over remote locations of Himalayan region provides an evidence of prevailing atmospheric transport processes, which further need to be well understood. It is expected that this work would be helpful in understanding the regional atmospheric conditions and the transboundary transport process of haze particles. As these informations are of great importance in modeling studies, which further lead to improve understanding of haze particles climate effects.Display Omitted
Keywords: Brown haze; TEM-EDX; Mixing states; Himalayas; Tibetan Plateau;

Soil and vegetation-atmosphere exchange of NO, NH3, and N2O from field measurements in a semi arid grazed ecosystem in Senegal by C. Delon; C. Galy-Lacaux; D. Serça; B. Loubet; N. Camara; E. Gardrat; I. Saneh; R. Fensholt; T. Tagesson; V. Le Dantec; B. Sambou; C. Diop; E. Mougin (36-51).
The alternating between dry and wet seasons and the consecutive microbial responses to soil water content in semiarid ecosystems has significant consequences on nitrogen exchanges with the atmosphere. Three field campaigns were carried out in a semi arid sahelian rangeland in Dahra (Ferlo, Senegal), two at the beginning of the wet season in July 2012 and July 2013, and the third one in November 2013 at the end of the wet season. The ammonia emission potentials of the soil ranged from 271 to 6628, indicating the soil capacity to emit NH3. The ammonia compensation point in the soil ranged between 7 and 150 ppb, with soil temperatures between 32 and 37 °C. Ammonia exchange fluctuated between emission and deposition (from −0.1–1.3 ng N.m−2 s−1), depending on meteorology, ambient NH3 concentration (5–11 ppb) and compensation point mixing ratios. N2O fluxes are supposed to be lower than NO fluxes in semi arid ecosystems, but in Dahra N2O fluxes (5.5 ± 1.3 ng N m−2 s−1 in July 2013, and 3.2 ± 1.7 ng N m−2 s−1 in November 2013) were similar to NO fluxes (5.7 ± 3.1 ng N m−2 s−1 in July 2012, 5.1 ± 2.1 ng N m−2 s−1 in July 2013, and 4.0 ± 2.2 ngN m−2 s−1 in November 2013). Possible reasons are the influence of soil moisture below the surface (where N2O is produced) after the beginning of the wet season, the potential aerobic denitrification in microsites, the nitrifier denitrification, and nitrification processes. The presence of litter and standing straw, and their decomposition dominated N compounds emissions in November 2013, whereas emissions in July 2012 and 2013, when the herbaceous strata was sparse, were dominated by microbial processes in the soil. CO2 respiration fluxes were high in the beginning (107 ± 26 mg m−2 h−1 in July 2013) and low in the end of the wet season (32 ± 5 mg m−2 h−1 in November 2013), when autotrophic and heterotrophic activity is reduced due to low soil moisture conditions These results confirm that contrasted ecosystem conditions due to drastic changes in water availability in semi arid regions have important non linear impacts on the biogeochemical nitrogen cycle.
Keywords: Nitrogen compound exchanges; Semi arid tropical ecosystem; Biogenic emissions; Litter emissions; Soil respiration; Soil processes of nitrogen release;

Development of land-use regression models for exposure assessment to ultrafine particles in Rome, Italy by Giorgio Cattani; Alessandra Gaeta; Alessandro Di Menno di Bucchianico; Antonella De Santis; Raffaela Gaddi; Mariacarmela Cusano; Carla Ancona; Chiara Badaloni; Francesco Forastiere; Claudio Gariazzo; Roberto Sozzi; Marco Inglessis; Camillo Silibello; Elisabetta Salvatori; Fausto Manes; Giulia Cesaroni (52-60).
The health effects of long-term exposure to ultrafine particles (UFPs) are poorly understood. Data on spatial contrasts in ambient ultrafine particles (UFPs) concentrations are needed with fine resolution. This study aimed to assess the spatial variability of total particle number concentrations (PNC, a proxy for UFPs) in the city of Rome, Italy, using land use regression (LUR) models, and the correspondent exposure of population here living. PNC were measured using condensation particle counters at the building facade of 28 homes throughout the city. Three 7-day monitoring periods were carried out during cold, warm and intermediate seasons. Geographic Information System predictor variables, with buffers of varying size, were evaluated to model spatial variations of PNC. A stepwise forward selection procedure was used to develop a “base” linear regression model according to the European Study of Cohorts for Air Pollution Effects project methodology. Other variables were then included in more enhanced models and their capability of improving model performance was evaluated. Four LUR models were developed. Local variation in UFPs in the study area can be largely explained by the ratio of traffic intensity and distance to the nearest major road. The best model (adjusted R2 = 0.71; root mean square error = ±1,572 particles/cm³, leave one out cross validated R2 = 0.68) was achieved by regressing building and street configuration variables against residual from the “base” model, which added 3% more to the total variance explained. Urban green and population density in a 5,000 m buffer around each home were also relevant predictors. The spatial contrast in ambient PNC across the large conurbation of Rome, was successfully assessed. The average exposure of subjects living in the study area was 16,006 particles/cm³ (SD 2165 particles/cm³, range: 11,075–28,632 particles/cm³). A total of 203,886 subjects (16%) lives in Rome within 50 m from a high traffic road and they experience the highest exposure levels (18,229 particles/cm³). The results will be used to estimate the long-term health effects of ultrafine particle exposure of participants in Rome.
Keywords: Ultrafine particles; Particle number concentration; Land use regression; Spatial variation; Exposure assessment;

Through the analysis of pH value, EC, precipitation and wind speed of 402 precipitation samples in the source region of the Yangtze River from January 1, 2010 to December 31, 2015, especially for the analysis of the 14 acid rain events. The results showed that: the acid rain in the source region of the Yangtze River was mainly affected by the southwest monsoon and the westerly circulation. The occurrence of acid rain mainly controlled by industrial pollution and other pollutants coming from India and other surrounding areas. And the other cause was that because of the Qinghai Tibet highway and the Qinghai Tibet railway, there were a lot of cars coming and going. And there were people in the summer to plateau tourism increased year by year, and more for self-driving travelling. This added additional pollutants (automobile exhaust) for the source of the Yangtze River. During the period of sampling, the variation range of pH value was from 4.0 to 8.57, with the mean was 6.37. And the range of EC was from 5.2 to 124.4 μs/cm, the average was 27.59 μs/cm. The order of conductivity in the four seasons was Spring > Winter > Summer > Autumn. And the order of pH in four seasons was Summer > Spring = Winter > Autumn. The results are also helpful for further understanding the acid rain in the Tibetan Plateau and providing scientific basis for the effective prevention and control of acid rain.
Keywords: Acid rain; Backward trajectory simulation; Source region of the Yangtze River;

In this study, 52 paired gas and particle samples were collected from a suburban field in Guangzhou in 2012 using a high-volume active air sampler; they were then analysed for 30 polychlorinated biphenyl (PCB) congeners via gas chromatography with tandem mass spectrometry. Total PCB concentrations ranged from 97.4 to 853 pg m−3. This was a moderate level compared with other cities, undeveloped areas, and electronic waste disposal sites. Atmospheric concentrations of PCBs did not exhibit notable diurnal or seasonal variations, except for a few high measurement. Tetra- and tri-CBs were the predominant PCB compounds, with an average combined contribution of 81.9%. CB-77 was the dominant congener in the particle phase due to a few samples with extremely high mass fraction of CB-77 and relatively low concentrations of other PCBs. Based on measurements of pollution characteristics including diurnal and seasonal variations, we used correlation analysis, principal component analysis and back trajectory modeling to deduce that electronic manufacturing and recycling activities, pigment/paint production, and waste incineration plants are possible sources of PCBs in Guangzhou. Of these sources, the high observed contributions of CB-77 originated mainly from the pigment/paint industry.Display Omitted
Keywords: Pollution sources; PCBs; Suburban; Southern China;

Composition and sources of winter haze in the Bakken oil and gas extraction region by A.R. Evanoski-Cole; K.A. Gebhart; B.C. Sive; Y. Zhou; S.L. Capps; D.E. Day; A.J. Prenni; M.I. Schurman; A.P. Sullivan; Y. Li; J.L. Hand; B.A. Schichtel; J.L. Collett (77-87).
In the past decade increased use of hydraulic fracturing and horizontal drilling has dramatically expanded oil and gas production in the Bakken formation region. Long term monitoring sites have indicated an increase in wintertime aerosol nitrate and sulfate in this region from particulate matter (PM2.5) measurements collected between 2000 and 2010. No previous intensive air quality field campaign has been conducted in this region to assess impacts from oil and gas development on regional fine particle concentrations. The research presented here investigates wintertime PM2.5 concentrations and composition as part of the Bakken Air Quality Study (BAQS). Measurements from BAQS took place over two wintertime sampling periods at multiple sites in the United States portion of the Bakken formation and show regionally elevated episodes of PM2.5 during both study periods. Ammonium nitrate was a major contributor to haze episodes. Periods of air stagnation or recirculation were associated with rapid increases in PM2.5 concentrations. Volatile organic compound (VOC) signatures suggest that air masses during these episodes were dominated by emissions from the Bakken region itself. Formation rates of alkyl nitrates from alkanes revealed an air mass aging timescale of typically less than a day for periods with elevated PM2.5. A thermodynamic inorganic aerosol model (ISORROPIA) was used to investigate gas-particle partitioning and to examine the sensitivity of PM2.5 concentrations to aerosol precursor concentrations. Formation of ammonium nitrate, the dominant component, was most sensitive to ammonia concentrations during winter and to nitric acid concentrations during early spring when ammonia availability increases. The availability of excess ammonia suggests capacity for further ammonium nitrate formation if nitrogen oxide emissions increase in the future and lead to additional secondary formation of nitric acid.Display Omitted
Keywords: Oil and natural gas; Bakken; Aerosol; Particulate matter; Haze;

Projecting future summer mortality due to ambient ozone concentration and temperature changes by Jae Young Lee; Soo Hyun Lee; Sung-Chul Hong; Ho Kim (88-94).
Climate change is known to affect the human health both directly by increased heat stress and indirectly by altering environments, particularly by altering the rate of ambient ozone formation in the atmosphere. Thus, the risks of climate change may be underestimated if the effects of both future temperature and ambient ozone concentrations are not considered. This study presents a projection of future summer non-accidental mortality in seven major cities of South Korea during the 2020s (2016–2025) and 2050s (2046–2055) considering changes in temperature and ozone concentration, which were predicted by using the HadGEM3-RA model and Integrated Climate and Air Quality Modeling System, respectively. Four Representative Concentration Pathway (RCP) scenarios (RCP 2.6, 4.5, 6.0, and 8.5) were considered. The result shows that non-accidental summer mortality will increase by 0.5%, 0.0%, 0.4%, and 0.4% in the 2020s, 1.9%, 1.5%, 1.2%, and 4.4% in the 2050s due to temperature change compared to the baseline mortality during 2001–2010, under RCP 2.6, 4.5, 6.0, and 8.5, respectively, whereas the mortality will increase by 0.0%, 0.5%, 0.0%, and 0.5% in the 2020s, and 0.2%, 0.2%, 0.4%, and 0.6% in the 2050s due to ozone concentration change. The projection result shows that the future summer morality in South Korea is increased due to changes in both temperature and ozone, and the magnitude of ozone-related increase is much smaller than that of temperature-related increase, especially in the 2050s.
Keywords: Ozone; Climate change; Mortality; Projection;

Elevated production of NH4NO3 from the photochemical processing of vehicle exhaust: Implications for air quality in the Seoul Metropolitan Region by Michael F. Link; Jounghwa Kim; Gyutae Park; Taehyoung Lee; Taehyun Park; Zaeem Bin Babar; Kijae Sung; Pilho Kim; Seokwon Kang; Jeong Soo Kim; Yongjoo Choi; Jihawn Son; Ho-Jin Lim; Delphine K. Farmer (95-101).
A vehicle fleet representative of passenger vehicles driven in the Seoul Metropolitan Region was investigated for primary emissions and secondary chemistry. Exhaust was photochemically oxidized in a flow reactor to determine the ammonium nitrate (NH4NO3) aerosol formation potential from vehicles of gasoline, diesel and liquid petroleum gasoline (LPG) fuel types. Secondary formation of aerosol NH4NO3, was larger than primary emissions for all vehicle fuel types except diesel, for which negligible secondary NH4NO3 production was observed. Although diesel vehicles emitted more primary nitrogen oxides than other vehicle types, ammonia emitted from gasoline and liquid petroleum gasoline fuels types limited the secondary production of NH4NO3. The results suggest that gasoline and liquid petroleum gasoline vehicles with three-way catalysts could be an important source of ammonia for NH4NO3 aerosol formation in ammonia-limited environments, including the Seoul Metropolitan Region.
Keywords: Ammonium nitrate; Vehicular ammonia; Vehicle exhaust photochemical oxidation; Korean air quality;

Paradigms and commonalities in atmospheric source term estimation methods by Paul E. Bieringer; George S. Young; Luna M. Rodriguez; Andrew J. Annunzio; Francois Vandenberghe; Sue Ellen Haupt (102-112).
Modeling the downwind hazard area resulting from the unknown release of an atmospheric contaminant requires estimation of the source characteristics of a localized source from concentration or dosage observations and use of this information to model the subsequent transport and dispersion of the contaminant. This source term estimation problem is mathematically challenging because airborne material concentration observations and wind data are typically sparse and the turbulent wind field chaotic. Methods for addressing this problem fall into three general categories: forward modeling, inverse modeling, and nonlinear optimization. Because numerous methods have been developed on various foundations, they often have a disparate nomenclature. This situation poses challenges to those facing a new source term estimation problem, particularly when selecting the best method for the problem at hand. There is, however, much commonality between many of these methods, especially within each category. Here we seek to address the difficulties encountered when selecting an STE method by providing a synthesis of the various methods that highlights commonalities, potential opportunities for component exchange, and lessons learned that can be applied across methods.
Keywords: Atmospheric transport and dispersion; Source term estimation; Nonlinear optimization; Adjoint methods; Inverse modeling;

Factors and characteristics of ammonia, hydrogen sulfide, carbon dioxide, and particulate matter emissions from two manure-belt layer hen houses by Ji-Qin Ni; Claude A. Diehl; Lilong Chai; Yan Chen; Albert J. Heber; Teng-Teeh Lim; Bill W. Bogan (113-124).
Manure-belt layer hen houses are a relatively newer design and are replacing the old high-rise layer hen houses for egg production in USA. However, reliable aerial pollutant emission data from comprehensive and long-term on-farm monitoring at manure-belt houses are scarce. This paper reports the emission factors and characteristics of ammonia (NH3), hydrogen sulfide (H2S), carbon dioxide (CO2), and particulate matter (PM10) from two 250,000-bird capacity manure-belt layer hen houses (B-A and B-B) in northern Indiana, USA. The 2-year continuous field monitoring followed the Quality Assurance Project Plan of the National Air Emission Monitoring Study (NAEMS). Only days with more than 18 h (or 75%) of valid data were reported to avoid biased emission calculation. The results of 2-year average daily mean (ADM) gas emissions per hen from the two houses, excluding emissions from their manure shed, were 0.280 g for NH3, 1.952 mg for H2S, and 103.2 g for CO2. They were 67% lower for NH3, 77% higher for H2S, and 10% higher for CO2 compared with reported emissions from high-rise layer hen houses. Emissions of NH3 and CO2 exhibited evident seasonal variations. They were higher in winter than in summer and followed the NH3 and CO2 concentration seasonal patterns. Annual emission differences were observed for all the four pollutants. Reduced emissions of the three gases were shown during periods of layer hen molting and flock replacement. The 2-year ADM PM10 emission from B-B was 25.2 mg d−1 hen−1. A unique weekly PM10 emission pattern was identified for both houses. It was characterized with much lower Sunday emissions compared with the other single-day emissions of the week and was related to the weekly schedule of in-house production operations, including maintenance and cleaning.Display Omitted
Keywords: Air quality; Animal agriculture; Emission rates; NAEMS; Pollutant emissions; Poultry house; Weekly variation;

Observations of N2O5 and ClNO2 at a polluted urban surface site in North China: High N2O5 uptake coefficients and low ClNO2 product yields by Xinfeng Wang; Hao Wang; Likun Xue; Tao Wang; Liwei Wang; Rongrong Gu; Weihao Wang; Yee Jun Tham; Zhe Wang; Lingxiao Yang; Jianmin Chen; Wenxing Wang (125-134).
Dinitrogen pentoxide (N2O5) and its heterogeneous uptake product, nitryl chloride (ClNO2), play important roles in the nocturnal boundary layer chemistry. To understand the abundances and chemistry of N2O5 and ClNO2 in the polluted urban atmosphere in North China, field measurements were conducted by deploying a chemical ionization mass spectrometer in urban Ji'nan in September 2014. The observed surface N2O5 concentrations were relatively low, with an average nocturnal value of 22 pptv, although the source of NO3 was rather strong, i.e., the NO2 and O3 were at very high levels. The N2O5 concentration peaked in the early evening, which was associated with thermal power plant plumes and residual O3. Nocturnal N2O5 was lost very rapidly, mainly through heterogeneous reactions on aerosol surfaces. The estimated N2O5 uptake coefficient was in the range of 0.042–0.092, among the highest values obtained from ground based field measurements. The fast heterogeneous reaction of N2O5 on high loadings of aerosols generated relatively high levels of ClNO2, with an average nocturnal concentration of 132 pptv. Despite the rich chloride content in aerosols, the ClNO2 product yield was low, 0.014 and 0.082 in two nighttime cases, much lower than the calculated values from the experiment-derived parameterization. The suppressed chlorine activation in polluted urban atmospheres was possibly associated with the reduced hygroscopicity, solubility, and activity of chloride in complex ambient aerosols.
Keywords: Dinitrogen pentoxide; Nitryl chloride; Uptake coefficient; Product yield; Urban China;

Morphochemical characteristics and mixing state of long range transported wildfire particles at Ny-Ålesund (Svalbard Islands) by Beatrice Moroni; David Cappelletti; Stefano Crocchianti; Silvia Becagli; Laura Caiazzo; Rita Traversi; Roberto Udisti; Mauro Mazzola; Krzysztof Markowicz; Christoph Ritter; Tymon Zielinski (135-145).
A prolonged and exceptionally intense air mass advection event transporting biomass burning aerosols generated in Alaska affected Ny-Ålesund in the mid of July 2015. This paper reports the morphochemical characteristics and mixing state of individual aerosol particles collected during the event. To this aim aerosol samples were collected on nucleopore polycarbonate membrane filters using a DEKATI 12-stage low volume impactor and analyzed by scanning electron microscopy (SEM) techniques. Results of SEM investigations depict a complex aerosol characterized by an external mixing between a main part of carbonaceous organic particles (tar balls and organic particles), lower ammonium sulfate and minor potassium chloride and mineral dust amounts. The carbonaceous particles are spherical to slightly elongated and the organic particles show an internal mixing of low density organics and/or ammonium sulfate upon denser nuclei. Most particles are in the accumulation mode size range although the size and the morphology of the chloride and the sulfate salts evidence the growth of these species both in the air and upon the sampling membranes. Individual particle analyses were complemented by aerosol size distribution (Aerodynamic Particle Sizer, Scanning Mobility Particle Sizer) and optical (Particle Soot Absorption Photometer, nephelometer) measurements at ground level in order to retrieve the optical and radiative properties of the aerosol in the atmosphere and to predict the fate and behaviour of particles upon deposition at ground level. Individual particle analyses were also compared with bulk chemical analyses on daily sampling filters and back-trajectory analyses of the air mass movement in order to enucleate distinct sources of the aerosol during the long range transport.Display Omitted
Keywords: Biomass burning particles; SEM-EDS; Image analysis; Aerosol sources; Particle evolution;

Modelling and mapping heavy metal and nitrogen concentrations in moss in 2010 throughout Europe by applying Random Forests models by Stefan Nickel; Winfried Schröder; Werner Wosniok; Harry Harmens; Marina V. Frontasyeva; Renate Alber; Julia Aleksiayenak; Lambe Barandovski; Oleg Blum; Helena Danielsson; Ludwig de Temmermann; Anatoly M. Dunaev; Hilde Fagerli; Barbara Godzik; Ilia Ilyin; Sander Jonkers; Zvonka Jeran; Gunilla Pihl Karlsson; Pranvera Lazo; Sebastien Leblond; Siiri Liiv; Sigurður H. Magnússon; Blanka Mankovska; Javier Martínez-Abaigar; Juha Piispanen; Jarmo Poikolainen; Ion V. Popescu; Flora Qarri; Dragan Radnovic; Jesus Miguel Santamaria; Martijn Schaap; Mitja Skudnik; Zdravko Špirić; Trajce Stafilov; Eiliv Steinnes; Claudia Stihi; Ivan Suchara; Lotti Thöni; Hilde Thelle Uggerud; Harald G. Zechmeister (146-159).
This study explores the statistical relations between the concentration of nine heavy metals (HM) (arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), mercury (Hg), nickel (Ni), lead (Pb), vanadium (V), zinc (Zn)), and nitrogen (N) in moss and potential explanatory variables (predictors) which were then used for mapping spatial patterns across Europe. Based on moss specimens collected in 2010 throughout Europe, the statistical relation between a set of potential predictors (such as the atmospheric deposition calculated by use of two chemical transport models (CTM), distance from emission sources, density of different land uses, population density, elevation, precipitation, clay content of soils) and concentrations of HMs and nitrogen (N) in moss (response variables) were evaluated by the use of Random Forests (RF) and Classification and Regression Trees (CART). Four spatial scales were regarded: Europe as a whole, ecological land classes covering Europe, single countries participating in the European Moss Survey (EMS), and moss species at sampling sites. Spatial patterns were estimated by applying a series of RF models on data on potential predictors covering Europe. Statistical values and resulting maps were used to investigate to what extent the models are specific for countries, units of the Ecological Land Classification of Europe (ELCE), and moss species.Land use, atmospheric deposition and distance to technical emission sources mainly influence the element concentration in moss. The explanatory power of calculated RF models varies according to elements measured in moss specimens, country, ecological land class, and moss species. Measured and predicted medians of element concentrations agree fairly well while minima and maxima show considerable differences. The European maps derived from the RF models provide smoothed surfaces of element concentrations (As, Cd, Cr, Cu, N, Ni, Pb, Hg, V, Zn), each explained by a multivariate RF model and verified by CART, and thereby more information than the dot maps depicting the spatial patterns of measured values.RF is an eligible method identifying and ranking boundary conditions of element concentrations in moss and related mapping including the influence of the environmental factors.
Keywords: Atmospheric deposition; Biomonitoring; Ecological land classification Europe; Spatial reference systems;

Assessment of regional acidifying pollutants in the Athabasca oil sands area under different emission scenarios by Sunny Cho; Krish Vijayaraghavan; David Spink; Jaegun Jung; Ralph Morris; Ron Pauls (160-168).
Acid deposition is a potential environmental impact of oil sands development in the Athabasca Oil Sands Region (AOSR) in Northeastern Alberta. An acid deposition management framework has been established to manage this issue. This framework includes an acid deposition modelling and time-to-effect impact assessment component that was recently implemented for four acidifying emissions cases using the Community Multi-scale Air Quality (CMAQ) model. Predicted gross Potential Acid Input (PAI) deposition in the AOSR increases from the historical to existing case with further increases predicted in two future cases due to the projected increase in NOx emissions. On average the total predicted PAI deposition in the AOSR is approximately 40% sulphur deposition and 60% nitrogen deposition. Sulphur deposition decreases by 7% from the historical to existing cases due to the reductions in SO2 emissions that have occurred in the AOSR but increases by 5% from the existing to future case 1 and by 8% from existing to future case 2 even though continued AOSR SO2 emission decreases were modelled. This is likely the result of the deposition reduction associated with a single large reduction in SO2 emissions from one facility's main stack being offset elsewhere in the AOSR by deposition increases due to small increases in SO2 emissions from several in situ sources with shorter stacks. Average nitrogen deposition over the AOSR increases by 10% from the historical to existing case and then further increases by 10.6% from the existing case to future case 1 and by 12.3% from the existing case to future case 2. The increasing relevance of NOx emissions over SO2 emissions in the AOSR suggests that a robust treatment of nitrogen chemistry such as in CMAQ is required for conducting deposition assessments in the region. The modelling results provide information that can be used to inform oil sands emission management priorities in the context of acid deposition and nitrogen eutrophication impact minimization.
Keywords: Acid deposition; Acidifying compounds; Spatiotemporal deposition pattern; Athabasca oil sands region; Deposition modelling;

Factors controlling particle number concentration and size at metro stations by C. Reche; T. Moreno; V. Martins; M.C. Minguillón; T. Jones; E. de Miguel; M. Capdevila; S. Centelles; X. Querol (169-181).
An extensive air quality campaign was performed at differently designed station platforms in the Barcelona metro system, aiming to investigate the factors governing airborne particle number (N) concentrations and their size distributions. The study of the daily trends of N concentrations by different size ranges shows that concentrations of N0.3–10 are closely related with the schedule of the metro service. Conversely, the hourly variation of N0.007–10 (mainly composed of ultrafine particles) could be partly governed by the entrance of particles from outdoor emissions through mechanical ventilation. Measurements under different ventilation settings at three metro platforms reveal that the effect on air quality linked to changes in the tunnel ventilation depends on the station design. Night-time maintenance works in tunnels are frequent activities in the metro system; and after intense prolonged works, these can result in higher N concentrations at platforms during the following metro operating hours (by up to 30%), this being especially evident for N1–10. Due to the complex mixture of factors controlling N, together with the differences in trends recorded for particles within different size ranges, developing an air quality strategy at metro systems is a great challenge. When compared to street-level urban particles concentrations, the priority in metro air quality should be dealing with particles coarser than 0.3 μm. In fact, the results suggest that at narrow platforms served by single-track tunnels the current forced tunnel ventilation during operating hours is less efficient in reducing coarse particles compared to fine.
Keywords: Metro system; UFP; Size distribution; Forced ventilation;