Atmospheric Environment (v.104, #C)

A field-scale experiment was conducted in the spring of 2012 at a winter wheat cropland, aiming to quantify ammonia (NH3) emissions from surface fertilization under realistic cultivation conditions. Since the fertilization lasted about 20 days for hundreds of divided plots and three types of fertilizers were used (i.e., urea, ammonium sulfate and compound nitrogen-phosphorous-potassium fertilizer), the heterogeneity was one of the significant characteristics of the cropland NH3 emissions during the experiment, which is a great challenge for the classical micrometeorological methods to calculate NH3 fluxes. Based on continuous measurements of NH3 concentrations at two heights (2.5 m and 8 m) and detailed records of the fertilization plot by plot, an inverse dispersion method was employed to derive the heterogeneous NH3 emissions and the corresponding emission factors (EFs). The EFs derived from this experiment for urea, ammonium sulfate and compound fertilizer were 12.0% ± 3.1%, 8.5% ± 1.6% and 4.5% ± 1.7%, respectively. The EF of urea we obtained was lower than most of other domestic measurements and those used in the NH3 emission inventories in China. Measurements on EFs of ammonium sulfate and compound fertilizer are not available in China. However, the EFs of ammonium sulfate and compound fertilizer we obtained were comparable to those used in NH3 emission inventories of China.
Keywords: NH3 emission factor; Synthetic fertilizer; Field-scale experiment; Inverse dispersion method; North China Plain;

Despite the stringent emission reduction measures implemented in Beijing over the past decade, a series of unprecedentedly severe haze events hit this megacity in January 2013. It is of great interest to find out the cause so as to provide a scientific basis for refining emission control measures. In the present study, we examine long-term (2000–2014) surface meteorological observations and simulate four recent winter haze episodes in 2010–2014 using a coupled meteorology-chemistry model (WRF-Chem). In addition to confirming the large-scale meteorological anomalies in northern China, the analysis of local meteorological parameters revealed that January 2013 had more frequent sustained weak southerly winds and high relative humidity in Beijing. Comparison of WRF-Chem simulations of the four episodes unambiguously shows that the combination of anomalously strong contribution of local and regional sources resulted into the extreme event in 2013: meteorological anomalies caused thicker temperature inversion, lower boundary layer, and hence stronger local accumulation of PM2.5 in urban Beijing (212 μg m−3 in 2013 case vs. 112–114 μg m−3 in historical cases); longer duration of southerly winds transported more pollutants to urban area (107 μg m−3 vs. 38–82 μg m−3) from eastern China. Our study also suggests that, although the emissions in Beijing have been decreased, they were still the major contributor (61–77%) to surface-layer PM2.5 over the urban area in recent winter episodes. Since adverse weather conditions such as those in January 2013 are uncontrollable, to alleviate severe haze pollution, Beijing must further strengthen its emission reduction measures and similar control should be extended to the entire eastern China.
Keywords: Haze; Beijing; Meteorological anomaly; WRF-Chem; PM2.5;

Assessment of the BTEX concentrations and reactivity in a confined parking area in Rio de Janeiro, Brazil by Barbara Prestes de Castro; Gladson de Souza Machado; Glauco Favila Bauerfeldt; Julio Domingos Nunes Fortes; Eduardo Monteiro Martins (22-26).
In this work, the contribution of evaporative emissions from light passenger vehicles to the degradation of the air quality was investigated on the basis of the indoor quantification of the monoaromatic volatile compounds Benzene, Toluene, Ethylbenzene and Xylenes (BTEX), specifically, a confined shopping mall parking area in the northern zone of Rio de Janeiro, a site that represents the reality of the vehicular fleet of the Metropolitan Region of Rio de Janeiro. In order to evaluate the concentration of the BTEX compounds, samples were collected, by an active sampling system using charcoal cartridge as adsorbent. The samples were extracted with organic solvent and subsequently analyzed by gas chromatography-mass spectrometry (GCMS). The average results were 54.14 μg m−3 (benzene), 209.24 μg m−3 (toluene), 45.87 μg m−3 (ethylbenzene) and 118.93 μg m−3 (xylenes). These results are compared with results from the literature of vehicular emissions in confined spaces such as garages and tunnels. Possible correlations with emissions from moving vehicles, obtained from previous studies in a tunnel of large circulation and emissions obtained in other underground parkings, are also investigated. The results suggest different emission sources.Display Omitted
Keywords: BTEX; Parking; Indoor pollution; Reactivity scale;

USA emissions estimates of CH3CHF2, CH2FCF3, CH3CF3 and CH2F2 based on in situ observations at Mace Head by P.G. Simmonds; R.G. Derwent; A.J. Manning; A. McCulloch; S. O'Doherty (27-38).
We investigate the low level, surface-to-surface transport of five hydrofluorocarbons (HFC-152a, -134a, -143a, -125 and -32) from North America to the Advanced Global Atmospheric Gases Experiment (AGAGE) observing station at Mace Head, Ireland during 2005–2012. Using the UK Meteorological Office Numerical Atmospheric dispersion Modelling Environment (NAME) we select air masses, which are dominated by direct transport from the North American continent to Mace Head, thereby eliminating any significant influence from local or other regional sources. To estimate emissions of individual HFCs we use the interspecies correlation method with HFC-125 as the reference compound. We then compare these derived North American emissions with those reported to UNFCCC. Our results indicate an under-reporting of HFC-152a emissions by the USA to the UNFCCC, with an annual average difference of 24 Gg (9–36 Gg). For HFC-134a our estimated emissions indicate an over-reporting of USA reported emissions by 24 Gg (21–28 Gg). For HFC-143a USA reported emissions are lower than our estimates by 1.8 Gg (1–3.5 Gg); whereas for HFC-32 there is close agreement, within the uncertainties, between the USA emissions reported to UNFCCC and our emissions estimates. Combining our USA emissions estimates for HFC-152a, HFC-134a, HFC-143a and HFC-32 with the UNFCCC estimate for HFC-125 could contribute potentially 201 ± 36 Tg-CO2 eq yr−1 to atmospheric radiative forcing in 2011–2012. This compares with UNFCCC of 146 Tg-CO2 eq yr−1 for the same five HFCs.
Keywords: USA HFC emission estimates; HFC-152a; HFC-134a; HFC-143a; HFC-32; Interspecies correlation;

Lung burden and deposition distribution of inhaled atmospheric urban ultrafine particles as the first step in their health risk assessment by Imre Salma; Péter Füri; Zoltán Németh; Imre Balásházy; Werner Hofmann; Árpád Farkas (39-49).
Realistic median particle number size distributions were derived by a differential mobility particle sizer in a diameter range of 6–1000 nm for near-city background, city centre, street canyon and road tunnel environments in Budapest. Deposition of inhaled particles within airway generations of an adult woman was determined by a stochastic lung deposition model for sleeping, sitting, light and heavy exercise breathing conditions. Deposition fractions in the respiratory tract were considerable and constant for all physical activities with a mean of 56%. Mean deposition fraction in the extra-thoracic region averaged for the urban environments was decreasing monotonically from 26% for sleeping to 9.4% for heavy exercise. The mean deposition fractions in the tracheobronchial region were constant for the physical activities and urban environments with an overall mean of 12.5%, while the mean deposition fraction in the acinar region averaged for the urban locations increased monotonically with physical activity from 14.7% for sleeping to 34% for heavy exercise. The largest contribution of the acinar deposition to the lung deposition was 75%. The deposition rates in the lung were larger than in the extra-thoracic region, and the deposition rate in the lung was increasingly realised in the AC region by physical activity. It was the extra-thoracic region that received the largest surface density deposition rates; its loading was higher by 3 orders of magnitude than for the lung. Deposition fractions in the airway generations exhibited a distinct peak in the acinar region. The maximum of the curves was shifted to peripheral airway generations with physical activity. The shapes of the surface density deposition rate curves were completely different from those for the deposition rates, indicating that the first few airway generations received the highest surface loading in the lung.
Keywords: Exposure assessment; Respiratory deposition; Surface density deposition; Nanoaerosol; Stochastic lung deposition model;

Particulate concentrations during on-farm combustion of energy crops of different shapes and harvest seasons by S. Fournel; J.H. Palacios; R. Morissette; J. Villeneuve; S. Godbout; M. Heitz; P. Savoie (50-58).
The increasing energy costs and environmental concerns of farms have motivated the growing interest of agricultural producers in using farm-grown biomass as a substitute to fossil fuels for heat production. However, the use of non-woody biomass is facing challenges due to variability regarding chemical composition and fuel properties that may induce problems during combustion such as particulate matter (PM). The aim of this work was to measure and compare total PM concentrations during on-farm combustion of wood and four agricultural crops: short-rotation willow, switchgrass, miscanthus and reed canary grass. In order to study the influence of physicochemical properties, different shapes (pellets, chips and chopped grasses) and harvest seasons (fall and spring) were also evaluated. In this context, a representative small-scale (29 kW), multi-fuel boiler for light commercial use was utilized. The boiler was also non-catalytic so that the burning took place in a single combustion chamber. Overall, twelve different biomass fuels were tested and each product was burned three times. Mean PM concentration of wood (416 mg Nm−3 at 7 vol% O2) was lower than that of the four dedicated energy crops (505–1417 mg Nm−3 at 7 vol% O2). However, because of the high variability between the experiments, no statistical significance was observed at P > 0.1 level except in one case. The PM amounts were high compared to literature data and Quebec's environmental regulation mainly because of the boiler system used. Except for willow, pelletized products decreased PM levels by 22–52% compared to chopped materials. Bulky biomass of low density was unable to reach steady-state conditions and produced compounds associated with incomplete combustion including PM. Spring-harvested biomass fuels showed a PM reduction up to 48% compared to fall-harvested crops. This was likely due to a 20–60% decrease of several chemical elements in the biomass, namely S, Cl, K and P which are the main constituents of fly ash.
Keywords: Agricultural biomass; Energy crops; Combustion; Particulate matter; Physicochemical properties;

Effects of conservation tillage practices on ammonia emissions from Loess Plateau rain-fed winter wheat fields by Yang Yang; Chunju Zhou; Na Li; Kun Han; Yuan Meng; Xiaoxiao Tian; Linquan Wang (59-68).
Ammonia emissions from agricultural activities contribute to air pollution. For the rain-fed winter wheat system in the Loess Plateau there is a lack of information about ammonia emissions. Current study aimed to provide field data on ammonia emissions affected by conservation tillage practices and nitrogen applications. A two-year field experiment was conducted during 2011–2013 wheat growing seasons followed a split-plot design. Main plots consisted of one conventional tillage (CT, as the control) and five conservation tillage systems, i.e., stalk mulching (SM), film mulching (FM), ridge tillage (RT), ridge tillage with film mulch on the ridge (RTfm), and ridge tillage with film mulch on the ridge and stalk mulch in the furrow (RTfmsm); while subplots consisted of two nitrogen application rates, i.e., 0 and 180 kg N ha−1. Ammonia emissions were measured using an acid trapping method with vented chambers. Results showed ammonia fluxes peaked during the first 10 days after fertilization. On average, nitrogen application increased ammonia emissions by 26.5% (1.31 kg N ha−1) compared with treatments without nitrogen application (P < 0.05). Ammonia fluxes were strongly dependent on soil ammonium, moisture, and temperature. Tillage systems had significant effects on ammonia emissions. On average, conservation tillage practices reduced ammonia emissions by 7.7% (0.46 kg N ha−1) compared with conventional tillage (P < 0.05), with FM most effective. Deep-band application of nitrogen fertilizer, stalk mulches, and film mulches were responsible for reductions in ammonia emissions from nitrogen fertilization in conservation tillage systems, thus they were recommended to reduce ammonia emissions from winter wheat production regions in the southern Loess Plateau.
Keywords: Ammonia volatilization; Acid trapping method; Soil moisture; Nitrogen fertilizer;

The response to hemispherical and regional aircraft NOx emissions is explored by using two climate metrics: radiative forcing (RF) and Global Warming Potential (GWP). The global chemistry transport model, MOZART-3 CTM, is applied in this study for a series of incremental aircraft NOx emission integrations to different regions. It was found that the sensitivity of chemical responses per unit emission rate from regional aircraft NOx emissions varies with size of aircraft NOx emission rate and that climate metric values decrease with increasing aircraft NOx emission rates, except for Southeast Asia. Previous work has recognized that aircraft NOx GWPs may vary regionally. However, the way in which these regional GWPs are calculated are critical. Previous studies have added a fixed amount of NOx to different regions. This approach can heavily bias the results of a regional GWP because of the well-established sensitivity of O3 production to background NOx whereby the Ozone Production Efficiency (OPE) is greater at small background NOx. Thus, even a small addition of NOx in a clean-air area can produce a large O3 response. Using this ‘fixed addition’ method of 0.035 Tg(N) yr−1, results in the greatest effect observed for North Atlantic and Brazil, ∼10.0 mW m−2/Tg(N) yr−1. An alternative ‘proportional approach’ is also taken that preserves the subtle balance of local NOx–O3–CH4 systems with the existing emission patterns of aircraft and background NOx, whereby a proportional amount of aircraft NOx, 5% (N) yr−1, is added to each region in order to determine the response. This results in the greatest effect observed for North Pacific that with its net NOx RF of 23.7 mW m−2/Tg(N) yr−1 is in contrast with the ‘fixed addition’ method. For determining regional NOx GWPs, it is argued that the ‘proportional’ approach gives more representative results. However, a constraint of both approaches is that the regional GWP determined is dependent on the relative global emission pattern, so if that changes in the future, the regional NOx GWP will change.
Keywords: Aviation; Regional emissions; Nitrogen oxides; GWP; Non-linearities;

Source apportionment of air pollution exposures of rural Chinese women cooking with biomass fuels by Wei Huang; Jill Baumgartner; Yuanxun Zhang; Yuqin Wang; James J. Schauer (79-87).
Particulate matter (PM) from different sources may differentially affect human health. Few studies have assessed the main sources of personal exposure to PM and their contributions among residents of developing countries, where pollution sources differ from those in higher-income settings. 116 daily (24-h) personal PM2.5 exposure samples were collected among 81 women cooking with biomass fuels in two villages in rural Yunnan, China. The PM samples were analyzed for mass and chemical composition, including water-soluble organic carbon (WSOC), black carbon (BC), and molecular markers. We found black carbon, n-alkanes and levoglucosan dominated the most abundant fractions of the total measured species and average personal PM2.5 exposure was higher in winter than that in summer in both villages. The composition data were then analyzed using a positive matrix factorization (PMF) receptor model to identify the main PM emission sources contributing to women's exposures and to assess their spatial (between villages) and seasonal variation in our study setting. The 6-factor solution provided reasonably stable profiles and was selected for further analysis. Our results show that rural Chinese women cooking with biomass fuels are exposed to a variety of sources. The identified factors include wood combustion (41.1%), a cooking source (35.6%), a mobile source (12.6%), plant waxes (6.7%), pyrolysis combustion (3.0%), and secondary organic aerosols (SOA; 1.0%). The mean source contributions of the mobile source, cooking source, and wood combustion factor to PM2.5 exposure were significantly different between women living in the two study villages, whereas the mean SOA, wood combustion, and plant waxes factors differed seasonally. There was no relationship between source contributions and questionnaire-based measurements of source-specific exposures, implying that the impacts of source contributions on exposure are affected by complex spatial, temporal and behavioral patterns that are difficult to quantify using questionnaire-based measurements. Epidemiologic studies, health risk assessments, and intervention programs would benefit from a better understanding of the sources impacting PM exposure among populations in developing countries.
Keywords: Source apportionment; Personal exposure; Molecular marker; PM2.5; Positive matrix factorization (PMF);

Representativeness of air quality monitoring networks by Jan Duyzer; Dick van den Hout; Peter Zandveld; Sjoerd van Ratingen (88-101).
The suitability of European networks to check compliance with air quality standards and to assess exposure of the population was investigated. An air quality model (URBIS) was applied to estimate and compare the spatial distribution of the concentration of nitrogen dioxide (NO2) in ambient air in four large cities. The concentrations calculated at the location of the monitoring stations, compared well with the concentrations measured at the stations indicating that the models worked well. Therefore the calculated concentration distributions were used as a proxy for the actual concentration distributions across the cities. The distributions of these proxy concentrations across the city populations was determined and cumulative population distribution curves were estimated. The calculated annual mean values at the monitoring network stations were located on the population distribution curves to estimate the fractions of the populations that the monitoring network stations represent. This macro scale procedure is used to evaluate which subgroups of the monitoring stations can be reliably used to decide on compliance or to estimate the concentration the population is exposed to. In addition, the CAR model and Computational Fluid Dynamics (CFD) models are used to investigate the effect of micro scale siting of the monitoring stations within the streets.The following observations were made:- Berlin and London networks cover the distribution of concentrations to which the population is exposed rather well, while Stuttgart and Barcelona have stations at sites with mainly the higher concentrations and the exposure is covered less well.- The networks in London and Berlin, with a substantial number of urban background stations, seem fit to monitor the average population exposure, contrary to those in Stuttgart and Barcelona with only a limited number of these stations.- The concentrations measured at street stations hardly reflect the calculated differences in street pollution between the cities. In Stuttgart the stations are, in line with the EU directive, placed in the most polluted streets, while in other cities there are no stations in the streets with the highest pollution levels.- The concentrations measured at street stations – particularly where buildings inhibit ventilation – are very sensitive to the exact location within the street. Different siting choices may have an effect that for NO2 could reach up to 10 μg/m3 in realistic conditions. Street stations, representing only a small urban area, are not suitable for characterising the exposure of the general population.It is important to note that epidemiological studies whether investigating short term-effects or those studying long-term effects are potentially affected by the issues raised in the paper. Long-term cumulative exposure estimates that are based rather uncritically on monitoring data may be biased if the stations are not representative. It is recommended to use models to support the interpretation and spatial extrapolation of the results of measurements in existing networks. The use of models also relaxes the need for station relocation in inadequate networks, which often would compromise trend analysis. It also relaxes the importance of exact or detailed, comprehensive, station classifications since all stations can be used in exposure assessments.
Keywords: Air pollution; Monitoring; Networks; Nitrogen dioxide; Exposure;

Source identification of total mercury (TM) wet deposition using a Lagrangian particle dispersion model (LPDM) by Yong-Seok Seo; Young-Ji Han; Thomas M. Holsen; Eunhwa Choi; Kyung-Duk Zoh; Seung-Muk Yi (102-111).
Event-based precipitation samples for total mercury (TM) were collected with a modified MIC-B sampler concurrent with atmospheric gaseous oxidized mercury (GOM) and particulate bound mercury (PBM) concentrations in Seoul, Korea from January 2006 to December 2009 to: 1) determine the seasonal variations in TM wet deposition, 2) investigate contributions of GOM and PBM scavenging to mercury wet deposition, and 3) identify source areas contributing to the high TM wet deposition using a Lagrangian particle dispersion model (LPDM). The volume-weighted mean (VWM) TM concentration was highest in winter, while the wet deposition flux was highest in summer. Multiple linear regression showed that the scavenging coefficient (SC) for GOM was much higher than the SC for PBM indicating that GOM was more effectively scavenged by wet deposition than PBM. Joint-probability LPDM (JP-LPDM) indicated that the main sources of TM wet deposition were the industrial and coastal areas in China and Japan.Display Omitted
Keywords: Total mercury; Gaseous oxidized mercury; Particulate bound mercury; Lagrangian particle dispersion model; Scavenging coefficient; Joint-probability LPDM;

In order to predict casualties caused by chemical hazards in densely populated areas, state-of-the-art Computational Fluid Dynamic (CFD) techniques could be utilized together with toxic load models. In the current study, simulations of consequences of hypothetical releases of toxic gas in a city center are presented and discussed. CFD models that reproduce flow statistics would be most appropriate for this purpose since it could be expected that they will more realistically represent the environment. However, since concentration-peaks in the ever-present spatiotemporal fluctuations of airborne chemicals contribute so much to the toxic load, it is shown that straight-forward direct linking of a CFD model to a toxic load model is not a suitable approach for predicting consequences of a toxic release. Furthermore, it is demonstrated that the use of different turbulence models leads to different casualty assessments. Obviously, there is an urgent need to establish widely accepted methods, ideally with known uncertainty measures. Thus, further research in this area is of great importance.Display Omitted
Keywords: Chemical hazard; Casualty assessments; Urban area; CFD; Toxic load;

Definition and determination of ozone laminae using Continuous Wavelet Transform (CWT) analysis by Guanyu Huang; M.J. Newchurch; Shi Kuang; Patrick I. Buckley; Wesley Cantrell; Lihua Wang (125-131).
Ozone laminae result from complex chemical and dynamical processes in the atmosphere. Unfortunately, there is no accepted definition of ozone laminae due to limited knowledge of the science determining their formation and evolution. Current methods to define ozone laminae are based on a reference profile that results from smoothing or linearly-regressing the original profile. These definitions are likely to underestimate the number of ozone laminae in the troposphere because the production of reference profiles reduces the information content in the original profiles. We present a method using the Continuous Wavelet Transform (CWT) with a two-threshold technique to define ozone laminae number and magnitude without requiring a reference profile. Our method encompasses an efficient and robust capability for identifying ozone laminae in the 15-year ozone profiles observed by ozonesondes in Huntsville, AL.
Keywords: Ozone laminae; Ozonesonde; Continuous Wavelet Transform; Tropospheric ozone;

The presence of black carbon, and size-resolved and total particle number concentrations (PNC) were investigated in the vicinity of Schiphol airport in the Netherlands, the fourth busiest airport in Europe. Continuous measurements were conducted between March and May 2014 at Adamse Bos, located 7 km from Schiphol, and in 2012 at Cabauw, a regional background site 40 km south of Schiphol. No significantly elevated black carbon levels were found near Schiphol. However, PNC increased during periods in which the wind direction was from Schiphol: at Cabauw by 20% and at Adamse Bos by a factor of three, from 14,100 (other wind directions) to 42,000 # cm−3 between 06.00 and 23.00. The size distribution of Schiphol-related PNC was dominated by ultrafine particles, ranging from 10 to 20 nm. Four relevant particle number (PN) emission sources at Schiphol were identified as being responsible for the elevated PNC levels at Adamse Bos: take-off and climb-out on the Kaagbaan and Aalsmeerbaan runways, planes waiting at the gates, and landing on the Buitenveldertbaan runway. PN emissions from road traffic at and near the airport were less important than air traffic. The exposure to Schiphol-related PNC in urban areas northeast of Schiphol in Amsterdam and Amstelveen was estimated for 2012 using a Gaussian Plume model. The results showed that a considerable number of the 555,000 addresses in the modelling domain were exposed to elevated PNC. For example: 45,000 addresses suffered long-term exposure to an additional annual background PNC of 5–10,000 # cm−3 originating from Schiphol and 60,000 addresses suffered short-term exposure (14% of the time) of additional 10–15,000 # cm−3 originating from Schiphol. Further research on emission sources and the dispersion of PN is recommended and may support future studies on eventual health effects.
Keywords: Airport emissions; Ultrafine particles; Black carbon; Dispersion modelling;

Evaluation of light dependence of monoterpene emission and its effect on surface ozone concentration by Hiroshi Nishimura; Hikari Shimadera; Akira Kondo; Hai Bao; Kundan Lal Shrestha; Yoshio Inoue (143-153).
This study evaluated the effect of light intensity on monoterpene emission from the three dominant coniferous tree species in Japan (Cryptomeria japonica, Chamaecyparis obtusa and Pinus densiflora). Monoterpene emission experiments were conducted by using a growth chamber where temperature and light intensity can be controlled. In the experiments, air temperature was set at 30 °C and light intensity was set at 0, 500, 700, 850, 1200, and 1400 μmol m−2  s−1. Because monoterpene emissions from the three tree species similarly increased with increasing light intensity, a new empirical equation considering light dependence was proposed to estimate monoterpene emission. In addition, monoterpene emission in the Kinki region of Japan was estimated with and without light dependence using meteorological field produced by the Weather Research and Forecasting model (WRF) in summer 2010. The monoterpene emissions estimated with light dependence were larger than those without light dependence in the daytime under clear sky conditions and consistently smaller in the nighttime. In order to evaluate the effect of light dependence of monoterpene emission on ozone concentration in the Kinki region, two cases of air quality simulations by the Community Multiscale Air Quality model (CMAQ) were conducted using the monoterpene emission data estimated with and without light dependence. Comparisons of the two cases showed that the monoterpene emission changes due to light dependence slightly but systematically affected ozone concentrations. Monoterpene generally played a role of reducing ozone concentration in the CMAQ simulations. Consequently, because of the light dependence, the mean daily maximum ozone concentrations decreased by 0.3 ppb on average with a maximum of 2.2 ppb, and the mean daily minimum values increased by 0.4 ppb on average with a maximum of 1.8 ppb in the Kinki region in summer 2010.
Keywords: Monoterpenes; Light intensity; Japanese coniferous tree; Ozone; WRF/CMAQ;

Vanadium and tungsten release from V-based selective catalytic reduction diesel aftertreatment by Z. Gerald Liu; Nathan A. Ottinger; Christopher M. Cremeens (154-161).
Vanadium-based selective catalytic reduction (V-SCR) catalysts are currently used for the reduction of nitrogen oxides (NOx) in worldwide diesel applications including Euro IV, V, and VI as well as U.S. nonroad Tier 4 Final. Although V-SCR catalysts are attractive because of their high NOx conversion, low cost, resistance to sulfur poisoning, and ability to reduce hydrocarbon emissions, there is concern that V-SCR washcoat material (e.g., vanadium and tungsten) and its derivatives may be released into the atmosphere, potentially harming human health and the environment. In this study, vanadium and tungsten release measurements are made with both a reactor- and engine-based approach in order to determine the potential release of these metals from diesel exhaust aftertreatment systems that contain a V-SCR catalyst. Results for a commercially available V-SCR reveal that both V and W release begin at 500 °C, and both reactor- and engine-based methods are capable of measuring qualitatively similar release. Emissions with the engine-based method are higher at all temperatures evaluated, likely due to this method's ability to capture particle-phase and vapor-phase emissions which become particle-bound after their evolution from the catalyst surface. Certification relevant data (NRTC and NRSC) from a nonroad engine is used to understand probable emissions from V-SCR aftertreatment architectures. Finally, results from a V-SCR catalyst formulated for improved thermal durability illustrate that it is possible to increase the maximum temperature for V-SCR catalysts. This comprehensive understanding of the temperature dependence of vanadium and tungsten volatility can be used to further analyze the full impact of diesel aftertreatment on exhaust emissions and their impact on human health and environmental toxicity.Display Omitted
Keywords: Vanadium; Tungsten; SCR; Diesel exhaust aftertreatment; Environmental toxicity;

To develop a coherent picture of possible origin of Asian aerosol, transport and meteorological interaction; wintertime aerosol (January, 1 to March, 31, 2014 (n = 90)) were measured in middle IGP in terms of aerosol mass loading, optical properties, altitudinal distributions and both high and low altitude transportation. Both space-borne passive (Aqua and Terra MODIS) and active sensor (CALIPSO-CALIOP) based measurements were concurrently used over the selected transect (25°10′–25°19′N and 82°54′–83°4′E). Exceptionally high aerosol mass loading was recorded for PM10 (233 ± 58.37 μg m−3) and PM2.5 (138 ± 47.12 μg m−3). Daily variations of PM2.5/PM10 persist in a range of 0.25–0.97 (mean = 0.60 ± 0.14; n = 90) and were in accordance to computed Angstrom exponent (0.078–1.407; mean: 1.002 ± 0.254) explaining concurrent contribution of both PM2.5 and PM10 for the region. Space borne (Aqua MODIS-AOD: 0.259–2.194) and ground based (MTP-AOD: 0.066–1.239) AODs revealed significant temporal variability and moderate association in terms of PM10 (MODIS-AOD: 0.46; MTP-AOD: 0.56) and PM2.5 (MODIS-AOD: 0.54; MTP-AOD: 0.39). Varying association of AOD and aerosol mass loading was also explained in terms of meteorological variables. CALIPSO altitude-orbit-cross-section profiles revealed presence of non-spherical coarse particulates (altitude: 1.2–5.4 km) and dominance of spherical fine particulates (altitude: 0.1–4.2 km). Contribution of trans-boundary aerosols transportation to mass loadings at middle IGP were recognized through lagrangian particle dispersion model, synoptic vector wind profiles at different geopotential heights and satellite images.Exceptionally high aerosol loading found moderately correlated with meteorology, space-borne and ground-based AODs; deposited in varying altitudes and governed by synoptic wind pattern.
Keywords: Aerosol; Aerosol optical depth; CALIPSO; Indo-Gangetic Plain; MODIS; Trans-boundary;

Particle-size distribution of polybrominated diphenyl ethers (PBDEs) in the urban agglomeration of Thessaloniki, northern Greece by Athanasios Besis; Elisavet Botsaropoulou; Dimitra Voutsa; Constantini Samara (176-185).
The size distribution of Polybrominated Diphenyl Ethers (PBDEs) in particle sizes <0.49, 0.49–0.97, 0.97–1.5, 1.5–3.0, 3.0–7.2 and >7.2 μm was measured during the cold and the warm period of the year 2013 at traffic and background sites in the urban agglomeration of Thessaloniki, northern Greece. Mean aggregate concentrations (sum of six particle fractions) of the sum of 12 PBDE congeners (∑12PBDE) were 20.3 and 2.1 pg m−3 at the traffic and the urban background site, respectively, in the cold period exhibiting relative increase (27.1 and 2.4 pg m−3, respectively) in the warm period. At both sampling sites, more than 58% of ∑12PBDE was found to be associated with particles smaller than 0.49 μm in diameter. The outdoor workday inhalation exposure to PBDEs was estimated by calculating daily intake values for respirable, thoracic and inhalable fractions.
Keywords: Polybrominated diphenyl ethers; Particle-size distribution; Urban atmosphere; Intake; Human exposure; Greece;

Airborne viable fungi in school environments in different climatic regions – A review by Heidi Salonen; Caroline Duchaine; Mandana Mazaheri; Sam Clifford; Sanna Lappalainen; Kari Reijula; Lidia Morawska (186-194).
Elevated levels of fungi in indoor environments have been linked with mould/moisture damage in building structures. However, there is a lack of information about “normal” concentrations and flora as well as guidelines of viable fungi in the school environment in different climatic conditions. We have reviewed existing guidelines for indoor fungi and the current knowledge of the concentrations and flora of viable fungi in different climatic areas, the impact of the local factors on concentrations and flora of viable fungi in school environments. Meta-regression was performed to estimate the average behaviour for each analysis of interest, showing wide variation in the mean concentrations in outdoor and indoor school environments (range: 101–103 cfu/m3). These concentrations were significantly higher for both outdoors and indoors in the moderate than in the continental climatic area, showing that the climatic condition was a determinant for the concentrations of airborne viable fungi. The most common fungal species both in the moderate and continental area were Cladosporium spp. and Penicillium spp. The suggested few quantitative guidelines for indoor air viable fungi for school buildings are much lower than for residential areas. This review provides a synthesis, which can be used to guide the interpretation of the fungi measurements results and help to find indications of mould/moisture in school building structures.
Keywords: Viable fungi; School environment; Climate areas; Concentrations; Flora; Guidelines;

Uncontrolled combustion of shredded tires in a landfill – Part 1: Characterization of gaseous and particulate emissions by Jared Downard; Ashish Singh; Robert Bullard; Thilina Jayarathne; Chathurika M. Rathnayake; Donald L. Simmons; Brian R. Wels; Scott N. Spak; Thomas Peters; Douglas Beardsley; Charles O. Stanier; Elizabeth A. Stone (195-204).
In summer 2012, a landfill liner comprising an estimated 1.3 million shredded tires burned in Iowa City, Iowa. During the fire, continuous monitoring and laboratory measurements were used to characterize the gaseous and particulate emissions and to provide new insights into the qualitative nature of the smoke and the quantity of pollutants emitted. Significant enrichments in ambient concentrations of CO, CO2, SO2, particle number (PN), fine particulate (PM2.5) mass, elemental carbon (EC), and polycyclic aromatic hydrocarbons (PAH) were observed. For the first time, PM2.5 from tire combustion was shown to contain PAH with nitrogen heteroatoms (a.k.a. azaarenes) and picene, a compound previously suggested to be unique to coal-burning. Despite prior laboratory studies' findings, metals used in manufacturing tires (i.e. Zn, Pb, Fe) were not detected in coarse particulate matter (PM10) at a distance of 4.2 km downwind. Ambient measurements were used to derive the first in situ fuel-based emission factors (EF) for the uncontrolled open burning of tires, revealing substantial emissions of SO2 (7.1 g kg−1), particle number (3.5 × 1016 kg−1), PM2.5 (5.3 g kg−1), EC (2.37 g kg−1), and 19 individual PAH (totaling 56 mg kg−1). A large degree of variability was observed in day-to-day EF, reflecting a range of flaming and smoldering conditions of the large-scale fire, for which the modified combustion efficiency ranged from 0.85 to 0.98. Recommendations for future research on this under-characterized source are also provided.Display Omitted
Keywords: Tire fire; Emission factor; Particle size distribution; PAH; Azaarenes; Iowa city;

Atmospheric boundary layer and ozone-aerosol interactions under Saharan intrusions observed during AMISOC summer campaign by J.A. Adame; C. Córdoba-Jabonero; M. Sorribas; D. Toledo; M. Gil-Ojeda (205-216).
A research campaign was performed for the AMISOC (Atmospheric Minor Species relevant to the Ozone Chemistry) project at El Arenosillo observatory (southwest Spain) in May–June 2012. The campaign focused on the impact of Saharan dust intrusions at the atmospheric boundary layer (ABL) and ozone-aerosol interactions. In-situ and remote-sensing techniques for gases and aerosols were used in addition to modelling analyses. Meteorology features, ABL structures and evolution, aerosol profiling distributions and aerosol–ozone interactions on the surface were analysed. Two four-day periods were selected according to non-dusty (clean conditions) and dusty (Saharan dust) situations. In both scenarios, sea-land breezes developed in the lower atmosphere, but differences were found in the upper levels. Results show that surface temperatures were greater than 3 °C and humidity were lower during dusty than non-dusty conditions. Thermal structures on the surface layer (estimated using an instrument on a 100 m tower) show differences, mainly during nocturnal periods with less intense inversions under dusty conditions. The mixing layer during dusty days was 400–800 m thick, less than observed on non-dusty. Dust also disturbed the typical daily ABL evolution. Stable conditions were observed in the early evening during intrusions. Aerosol extinction on dusty days was 2–3 times higher, and the dust was confined between 1500 and 5500 m. Back trajectory analyses confirmed that the dust had an African origin. On surface, the particle concentration was approximately 3.5 times higher during dusty events, but the local ozone did not exhibit any change. The arrival of Saharan dust in the upper levels impacted the meteorological surface, inhibited the daily evolution of the ABL and caused an increase in aerosol loading on the surface and at higher altitudes; however, no dust influence was observed on the surface ozone.
Keywords: Saharan dust; ABL; Ozone; Aerosol;

The impacts of the diurnal variation of surface temperature on street canyon flow pattern and pollutant dispersion are investigated based on a two-dimensional street canyon model under different thermal stratifications. Uneven distributed street temperature conditions and a user-defined wall function representing the heat transfer between the air and the street canyon are integrated into the current numerical model. The prediction accuracy of this model is successfully validated against a published wind tunnel experiment. Then, a series of numerical simulations representing four time scenarios (Morning, Afternoon, Noon and Night) are performed at different Bulk Richardson number (Rb). The results demonstrate that uneven distributed street temperature conditions significantly alters street canyon flow structure and pollutant dispersion characteristics compared with conventional uniform street temperature assumption, especially for the morning event. Moreover, air flow patterns and pollutant dispersion are greatly influenced by diurnal variation of surface temperature under unstable stratification conditions. Furthermore, the residual pollutant in near-ground-zone decreases as Rb increases in noon, afternoon and night events under all studied stability conditions.
Keywords: Street canyon; Street temperature; Diurnal variation; Pollutant dispersion;

Long term observations of PM2.5-associated PAHs: Comparisons between normal and episode days by Jia Wang; Xiao Li; Nan Jiang; Wenkai Zhang; Ruiqin Zhang; Xiaoyan Tang (228-236).
The pollution characteristic of fine particular matter (PM2.5) and associated polycyclic aromatic hydrocarbons (PAHs) are currently drawing a great deal of interest because of their influence on environment and health. In this study, PM2.5 was collected from 2011 to 2013 (n = 188) in a suburban area of Zhengzhou, China. 16-PAHs were analyzed to determine the concentration, seasonal variation and potential sources during normal days and episode events. The total mass of 16 PAHs and PM2.5 were in the range of 7–961 ng m−3 and 55–697 μg m−3, with a 3-year average of 174 ng m−3 and 194 μg m−3 respectively. Winter is most polluted for both PM2.5 and PAHs. Average PAH and PM2.5 concentrations during three episode events are 454 ng m−3 and 453 μg m−3, respectively, much higher than values during normal days (299 ng m−3 and 180 μg m−3, respectively). Ratios of Σ16PAH/PM2.5 varied with seasons and concentrations of PM2.5, but showed a negative correlation with PM2.5 concentrations during episode events. The dominant components of PAHs are Benzo[b]fluoranthene, Chrysene, Fluoranthene, and Benzo[k]fluoranthene, Benz[a]anthracene, Pyrene, Indeno(1,2,3-cd)pyrene and their total concentrations vary from 27 to 342 ng m−3, accounting for 58–82% (average = 73%) of 16 PAHs. The Benzo[a]pyrene (Bap) concentration obtained was 9.4 ng m−3 (3-year average), exceeding nearly one order of magnitude of ambient air BaP standard (annual average: 1.0 ng m−3) in China. Diagnose ratios and Positive Matrix Factorization results show that coal combustion, vehicles, coking plant, and biomass burning are main sources for PAHs in this area. The high concentrations of PM2.5 and PAHs, especially during episode events, reflected a potential health problem for nearby public and the necessity of air pollution control for both stationary and mobile sources.
Keywords: PM2.5; PAHs; Episode events; PMF; Diagnose ratios; BaP;

PM emissions measurements of in-service commercial aircraft engines during the Delta-Atlanta Hartsfield Study by Prem Lobo; Donald E. Hagen; Philip D. Whitefield; David Raper (237-245).
This paper describes the results of the physical characterization of aircraft engine PM emission measurements conducted during the Delta-Atlanta Hartsfield Study at the Hartsfield-Jackson Atlanta International Airport. Engine exit plane PM emissions were sampled from on-wing engines on several in-service commercial transport aircraft from the fleet of Delta Airlines. The size distributions were lognormal in nature with a single mode. The geometric mean diameter was found to increase with increasing engine thrust, ranging from 15 nm at idle to 40 nm at takeoff. PM number- and mass-based emission indices were observed to be higher at the idle conditions (4% and 7%), lowest at 15%–30% thrust, and then increase with increasing thrust. Emissions measurements were also conducted during an advected plume study where over 300 exhaust plumes generated by a broad mix of commercial transports were sampled 100–350 m downwind from aircraft operational runways during normal airport operations. The range of values measured at take-off for the different engine types in terms of PM number-based emission index was between 7 × 1015–9 × 1017 particles/kg fuel burned, and that for PM mass-based emission index was 0.1–0.6 g/kg fuel burned. PM characteristics of aircraft engine specific exhaust were found to evolve over time as the exhaust plume expands, dilutes with ambient air, and cools. The data from these measurements will enhance the emissions inventory development for a subset of engines operating in the commercial fleet and improve/validate current environmental impact predictive tools with real world aircraft engine specific PM emissions inputs.
Keywords: PM emissions; Aircraft engines; Emission index; Hartsfield-Jackson Atlanta International Airport; Plume evolution;

Associations between personal exposures to VOCs and alterations in cardiovascular physiology: Detroit Exposure and Aerosol Research Study (DEARS) by Hwashin Hyun Shin; Paul Jones; Robert Brook; Rob Bard; Karen Oliver; Ron Williams (246-255).
An adult cohort consisting of 63 participants engaged in the US EPA's recent Detroit Exposure and Aerosol Research Study (DEARS) and a University of Michigan cardiovascular sub-study conducted during summer and winter periods over 3 years between 2004 and 2007 (5 seasons in total). Through all participants' wearing of a monitoring vest, personal exposures to various air pollutants were measured.The study objective was to identify the association between personal exposure to volatile organic compounds (VOCs) and six cardiovascular health endpoints in an adult non-smoking cohort of the DEARS.Twenty five VOCs were collected using the DEARS exposure vest incorporating advanced passive diffusion tube. Six cardiovascular health endpoints including systolic and diastolic blood pressure (SBP, DBP), heart rate (HR), brachial artery diameter (BAD), brachial artery flow-mediated dilatation (FMD) and nitroglycerin-mediated arterial dilatation (NMD) were collected by novel, in-home clinical examinations. To reduce the number of personal VOCs highly correlated to each other, a principal component analysis was conducted. Accounting for more individual variations in association between personal VOCs and cardiovascular health endpoints, a linear mixed model was employed, where cohort subjects were not necessarily to have the same linear association.Applying the principal component analysis, 3 out of 12 components were retained, which appeared to involve a petroleum source (1st component), a 1-3 butadiene source (2nd component), and an ambient (Freon) source (3rd component). Petroleum related VOCs were associated with increases in FMD and showed mixed relationships with NMD (lag 0–1 day increased NMD, lag 2 days decreased NMD). Butadiene related VOCs decreased DBP but increased HR and BAD. Freon (ambient background) related VOCs increased HR.We observed mixed and variable results in this first study to evaluate the relationships between personal exposures to VOCs of different origin on cardiovascular physiology. In sum, the findings suggest that VOCs may have rapid impacts upon the human cardiovascular system; however, understanding the health implications and the mechanisms responsible is beyond the scope of this investigation.
Keywords: Cardiovascular; Exposure assessment; Volatile organic compounds; Principal component analysis; DEARS; Linear Mixed model;

Land use regression modeling with vertical distribution measurements for fine particulate matter and elements in an urban area by Chi-Chang Ho; Chang-Chuan Chan; Chien-Wen Cho; Hung-I Lin; Jui-Huan Lee; Chang-Fu Wu (256-263).
Land use regression (LUR) models have been developed and applied to evaluate long-term exposure to air pollutants in residential area. However, adopting LUR models for vertical distributions of PM2.5 elemental composition has not been studied extensively. Developing this type of LUR model in various urban areas is essential to examine the influence of sampling height from ground level on the modeling prediction of these pollutants. The purpose of this study was to examine spatial variations of exposures to PM2.5 and PM2.5 composition in an urban area and build LUR models with vertical distribution measurements. PM2.5 samples were collected at twenty low-level sites (first to third floors), five mid-level sites (fourth to sixth floors), and five high-level sites (seventh to ninth floors). LUR models considering local land use data and traffic information were developed for PM2.5 and elements (i.e., silicon (Si), sulfur (S), potassium (K), titanium (Ti), manganese (Mn), iron (Fe), nickel (Ni), copper (Cu), and zinc (Zn)). The results demonstrated that the vertical ratios were higher than 1 (i.e., highest concentrations at low-level sites) for PM2.5, Si, Ti, and Fe. Their median ratios ranged from 1.05 to 1.18. The explained variances (R2) of LUR models ranged from 0.46 to 0.80. Traffic and industrial land were major variables in most models, and the floor level was identified as a significant predictor in the PM2.5, Si, and Fe models. This indicated the necessity of collecting vertically distributed measurements in future LUR studies for reducing the exposure bias in epidemiological studies.
Keywords: Land use regression; Vertical variability; Fine particulate matter; Elemental composition;

At road intersections, vehicles frequently stop with idling engines during the red-light period and speed up rapidly in the green-light period, which generates higher velocity fluctuation and thus higher emission rates. Additionally, the frequent changes of wind direction further add the highly variable dispersion of pollutants at the street scale. It is, therefore, very difficult to estimate the distribution of pollutant concentrations using conventional deterministic causal models.For this reason, a hybrid model combining wavelet neural network and genetic algorithm (GA–WNN) is proposed for predicting 5-min series of carbon monoxide (CO) and fine particulate matter (PM2.5) concentrations in proximity to an intersection. The proposed model is examined based on the measured data under two situations. As the measured pollutant concentrations are found to be dependent on the distance to the intersection, the model is evaluated in three locations respectively, i.e. 110 m, 330 m and 500 m. Due to the different variation of pollutant concentrations on varied time, the model is also evaluated in peak and off-peak traffic time periods separately. Additionally, the proposed model, together with the back-propagation neural network (BPNN), is examined with the measured data in these situations. The proposed model is found to perform better in predictability and precision for both CO and PM2.5 than BPNN does, implying that the hybrid model can be an effective tool to improve the accuracy of estimating pollutants' distribution pattern at intersections. The outputs of these findings demonstrate the potential of the proposed model to be applicable to forecast the distribution pattern of air pollution in real-time in proximity to road intersection.
Keywords: Carbon monoxide; Fine particulate matter; Fine-scale estimation; Wavelet neural network; Genetic algorithm; Road intersection;

Uncontrolled combustion of shredded tires in a landfill – Part 2: Population exposure, public health response, and an air quality index for urban fires by Ashish Singh; Scott N. Spak; Elizabeth A. Stone; Jared Downard; Robert L. Bullard; Mark Pooley; Pamela A. Kostle; Matthew W. Mainprize; Michael D. Wichman; Thomas M. Peters; Douglas Beardsley; Charles O. Stanier (273-283).
The Iowa City Landfill in eastern Iowa, United States, experienced a fire lasting 18 days in 2012, in which a drainage layer of over 1 million shredded tires burned, generating smoke that impacted the surrounding metropolitan area of 130,000 people. This emergency required air monitoring, risk assessment, dispersion modeling, and public notification. This paper quantifies the impact of the fire on local air quality and proposes a monitoring approach and an air quality index (AQI) for use in future tire fires and other urban fires. Individual fire pollutants are ranked for acute and cancer relative risks using hazard ratios, with the highest acute hazard ratios attributed to SO2, particulate matter, and aldehydes. Using a dispersion model in conjunction with the new AQI, we estimate that smoke concentrations reached unhealthy outdoor levels for sensitive groups out to distances of 3.1 km and 18 km at 24-h and 1-h average times, respectively. Modeled and measured concentrations of PM2.5 from smoke and other compounds such as VOCs and benzo[a]pyrene are presented at a range of distances and averaging times, and the corresponding cancer risks are discussed. Through reflection on the air quality response to the event, consideration of cancer and acute risks, and comparison to other tire fires, we recommend that all landfills with shredded tire liners plan for hazmat fire emergencies. A companion paper presents emission factors and detailed smoke characterization.Display Omitted
Keywords: Air quality index; Tire fire; Iowa City; Hazard ratio;