Atmospheric Environment (v.44, #3)

The impact of transportation control measures on emission reductions during the 2008 Olympic Games in Beijing, China by Yu Zhou; Ye Wu; Liu Yang; Lixin Fu; Kebin He; Shuxiao Wang; Jiming Hao; Jinchuan Chen; Chunyan Li (285-293).
Traffic congestion and air pollution were two major challenges for the planners of the 2008 Olympic Games in Beijing. The Beijing municipal government implemented a package of temporary transportation control measures during the event. In this paper, we report the results of a recent research project that investigated the effects of these measures on urban motor vehicle emissions in Beijing. Bottom–up methodology has been used to develop grid-based emission inventories with micro-scale vehicle activities and speed-dependent emission factors. The urban traffic emissions of volatile organic compounds (VOC), carbon monoxide (CO), nitrogen oxides (NOx) and particulate matter with an aerodynamic diameter of 10 μm or less (PM10) during the 2008 Olympics were reduced by 55.5%, 56.8%, 45.7% and 51.6%, respectively, as compared to the grid-based emission inventory before the Olympics. Emission intensity was derived from curbside air quality monitoring at the North 4th Ring Road site, located about 7 km from the National Stadium. Comparison between the emission intensity before and during the 2008 Olympics shows a reduction of 44.5% and 49.0% in daily CO and NOx emission from motor vehicles. The results suggest that reasonable traffic system improvement strategies along with vehicle technology improvements can contribute to controlling total motor vehicle emissions in Beijing after the Olympic Games.
Keywords: Olympic Games; Transportation control measures; Emission inventory; Beijing;

In this paper the meteorological processes responsible for transporting tracer during the second ETEX (European Tracer EXperiment) release are determined using the UK Met Office Unified Model (UM). The UM predicted distribution of tracer is also compared with observations from the ETEX campaign. The dominant meteorological process is a warm conveyor belt which transports large amounts of tracer away from the surface up to a height of 4 km over a 36 h period. Convection is also an important process, transporting tracer to heights of up to 8 km. Potential sources of error when using an operational numerical weather prediction model to forecast air quality are also investigated. These potential sources of error include model dynamics, model resolution and model physics. In the UM a semi-Lagrangian monotonic advection scheme is used with cubic polynomial interpolation. This can predict unrealistic negative values of tracer which are subsequently set to zero, and hence results in an overprediction of tracer concentrations. In order to conserve mass in the UM tracer simulations it was necessary to include a flux corrected transport method. Model resolution can also affect the accuracy of predicted tracer distributions. Low resolution simulations (50 km grid length) were unable to resolve a change in wind direction observed during ETEX 2, this led to an error in the transport direction and hence an error in tracer distribution. High resolution simulations (12 km grid length) captured the change in wind direction and hence produced a tracer distribution that compared better with the observations. The representation of convective mixing was found to have a large effect on the vertical transport of tracer. Turning off the convective mixing parameterisation in the UM significantly reduced the vertical transport of tracer. Finally, air quality forecasts were found to be sensitive to the timing of synoptic scale features. Errors in the position of the cold front relative to the tracer release location of only 1 h resulted in changes in the predicted tracer concentrations that were of the same order of magnitude as the absolute tracer concentrations.
Keywords: Pollution transport; Mass conservation; UK Met Office Unified Model;

Carbon dioxide and methane fluxes in the littoral zones of two lakes, east Antarctica by Renbin Zhu; Yashu Liu; Hua Xu; Tao Huang; Jianjun Sun; Erdeng Ma; Liguang Sun (304-311).
During the summertime of 2007/2008, carbon dioxide (CO2) and methane (CH4) fluxes across air–water interface were investigated in the littoral zones of Lake Mochou and Lake Tuanjie, east Antarctica, using a static chamber technique. The mean fluxes of CO2 and CH4 were −70.8 mgCO2 m−2 h−1 and 144.6 μgCH4 m−2 h−1, respectively, in the littoral zone of Lake Mochou; The mean fluxes were −36.9 mgCO2 m−2 h−1 and 109.8 μgCH4 m−2 h−1, respectively, in the littoral zone of Lake Tuanjie. Their fluxes showed large temporal and spatial dynamics. The CO2 fluxes showed a significantly negative correlation with daily total radiation (DTR) and a weakly negative correlation with air temperature and water temperature, indicating that sunlight intensity controlled the magnitude of CO2 fluxes from the open lakes. The CH4 fluxes significantly correlated with local air temperature, water table and total dissolved solids (TDS), indicating that they were the predominant factors influencing CH4 fluxes. Summertime CO2 budgets in the littoral zones of Lake Mochou and Lake Tuanjie were estimated to be −152.9 gCO2 m−2 and −79.7 gCO2 m−2, respectively, and net CH4 emissions were estimated to be 312.3 mgCH4 m−2 and 237.2 mgCH4 m−2, respectively. Our results show that shallow, open, alga-rich lakes might be strong summertime CO2 absorbers and small CH4 emitters during the open water in coastal Antarctica.
Keywords: Carbon dioxide; Methane; Flux; Lake; Antarctica; Littoral zone;

Insights into the nature of secondary organic aerosol in Mexico City during the MILAGRO experiment 2006 by Elizabeth A. Stone; Curtis J. Hedman; Jiabin Zhou; Mark Mieritz; James J. Schauer (312-319).
This study targets understanding the secondary sources of organic aerosol in Mexico City during the Megacities Impact on Regional and Global Environment (MIRAGE) 2006 field campaign. Ambient PM2.5 was collected daily at urban and peripheral locations. Particle-phase secondary organic aerosol (SOA) products of anthropogenic and biogenic precursor gases were measured by gas chromatography mass spectrometry. Ambient concentrations of SOA tracers were used to estimate organic carbon (OC) from secondary origins (SOC). Anthropogenic SOC was estimated as 20–25% of ambient OC at both sites, while biogenic SOC was less abundant, but was relatively twice as important at the peripheral site. The OC that was not attributed secondary sources or to primary sources in a previous study showed temporal consistency with biomass-burning events, suggesting the importance of secondary processing of biomass-burning emissions in the region. The best estimate of biomass-burning-related SOC was in the range of 20–30% of ambient OC during peak biomass burning events. Low-molecular weight (MW) alkanoic and alkenoic dicarboxylic acids (C2–C5) were also measured, of which oxalic acid was the most abundant. The spatial and temporal trends of oxalic acid differed from tracers for primary and secondary sources, suggesting that it had different and/or multiple sources in the atmosphere.
Keywords: Secondary organic aerosol; Source apportionment; Water-soluble organic carbon; Mexico City;

Characterisation and source apportionment of fine particulate sources at Hanoi from 2001 to 2008 by David D. Cohen; Jagoda Crawford; Eduard Stelcer; Vuong Thu Bac (320-328).
PM2.5 particulate matter has been collected on Teflon filters every Sunday and Wednesday at Hanoi, Vietnam for nearly eight years from April 2001 to December 2008. These filters have been analysed for over 21 different chemical species from hydrogen to lead by ion beam analysis techniques. This is the first long term PM2.5 dataset for this region. The average PM2.5 mass for the study period was (54 ± 33) μg m−3, well above the current US EPA health goal of 15 μg m−3. The average PM2.5 composition was found to be (29 ± 8)% ammonium sulfate, (8.9 ± 3.3)% soil, (28 ± 11)% organic matter, (0.6 ± 1.4)% salt and (9.2 ± 2.8)% black carbon. The remaining missing mass (25%) was mainly nitrates and absorbed water. Positive matrix factorisation techniques identified the major source contributions to the fine mass as automobiles and transport (40 ± 10)%, windblown soil (3.4 ± 2)%, secondary sulfates (7.8 ± 10)%, smoke from biomass burning (13 ± 6)%, ferrous and cement industries (19 ± 8)%, and coal combustion (17 ± 7)% during the 8 year study period.
Keywords: Ion beam analysis; PMF; Fine particles; PM2.5; Air pollution sources; Hanoi;

Surface tensions for a wide variety of pure organic and mixed organic/salt solutions were measured at 25 and 5 °C using the Wilhelmy plate method. Langmuir adsorption parameters for the organic compounds were extracted by fitting the surface tension data to the Szyszkowski equation. In a mixed organic/salt solution, the surface tension was primarily controlled by the organic component, even when the mass ratio of salt to organic in solution exceeded threefold. Excellent agreement was found between measured surface tension values at 5 °C and those predicted by the Szyszkowski equation using Langmuir adsorption parameters extracted at 25 °C. This finding may have important implications for cloud formation studies where the onset of activation often occurs at temperatures below 25 °C.
Keywords: Organic aerosol; Cloud activation; Water-soluble organic carbon (WSOC); Humic substances;

Influence of Saharan dust outbreaks and atmospheric stability upon vertical profiles of size-segregated aerosols and water vapor by Joaquín Giménez; Carlos Pastor; Ramón Castañer; José Nicolás; Javier Crespo; Adoración Carratalá (338-346).
Vertical profiles of aerosols and meteorological parameters were obtained using a hot air balloon and motorized paraglider. They were studied under anticyclonic conditions in four different contexts. Three flights occurred near sunrise, and one took place in the central hours of the day. The effects of North African dust intrusions were analyzed, whose entrance to the study area took place above the Stable Boundary Layer (SBL) in flight 1 and below it in flight 2. These flights have been compared with a non-intrusion situation (flight 3). A fourth flight characterized the profiles in the central hours of the day with a well-formed Convective Boundary Layer (CBL). With respect to the particle number distribution, the results show that not all sizes increase within the presence of an intrusion; during the first flight the smallest particles were not affected. The particle sizes affected in the second flight fell within the 0.35–2.5 μm interval. Under situations of convective dynamics, the reduction percentage of the particle number concentration reduces with increasing altitude, independently of their size, with respect to stability conditions. The negative vertical gradient for aerosols and water vapor, characteristic of a highly stable SBL (flight 3) becomes a constant profile within a CBL (flight 4). There are two situations that seem to alter the negative vertical gradient of the water vapor mixing ratio within the SBL: the presence of an intrusion and the possible stratification of the SBL based on different degrees of stability.
Keywords: Saharan dust; Aerosol spectrometer; Stable boundary layer; Convective boundary layer; Water vapor;

Deposition processes of ionic constituents to snow cover by K. Osada; Y. Shido; H. Iida; M. Kido (347-353).
Atmospheric deposition is an important removal process of aerosol particles and gases from the atmosphere. To elucidate the relative contributions of wet and dry processes and in-cloud and below-cloud scavenging based on deposition amounts in winter at Mt. Tateyama, central Japan, we obtained daily samples (December, 2006–March, 2007) of size-segregated aerosol particles and precipitation at Senjyugahara (SJ; 475 m a.s.l.) and vertical samples of spring snow cover at Murododaira (MR, 2450 m a.s.l., 13 km distance from SJ) on the western flank of Mt. Tateyama. The NH4 + and nssSO4 2− in aerosols were mostly found in the fine fraction (<2 μm), although Na+, NO3 , and nssCa2+ were mainly detected in the coarse fraction (>2 μm). Average ionic concentrations (μg g−1) in precipitation at SJ were higher about 3.8 for Na+ and nssCa2+, 3.4 for NO3 , 3.7 for NH4 +, 2.5 for nssSO4 2− than those at MR, whereas cumulative precipitation amounts at SJ and MR were, respectively, 84 and 175 cm of water equivalent. Wet and dry deposition amounts during the study period were estimated for sites using size-segregated aerosol data, winter averages of HNO3, NH3, and SO2 concentrations, and dry deposition velocities. Particle-dry deposition comprised about 3% (Na+) to 11% (NH4 +) of the total deposition at MR. The maximum amounts of gas dry deposition were estimated, respectively, as 4, 13, and 3% of the total deposition at MR for NH4 +, NO3 , and nssSO4 2−. The relative contributions of below-cloud scavenging (BCS) between MR and SJ were estimated as considering the wet only deposition amount at MR. Higher contributions of BCS were obtained for Na+ (56%) and nssCa2+ (45%), whereas BCSs for NH4 +, NO3 , and nssSO4 2− were lower than 28%. Ionic constituents existing predominantly in the coarse fraction showed a large contribution of BCS.
Keywords: Acid deposition; Scavenging process; Eastern Asia; Mountain slope; Mount Tateyama;

Odour impact assessment by means of dynamic olfactometry, dispersion modelling and social participation by Selena Sironi; Laura Capelli; Paolo Céntola; Renato Del Rosso; Sauro Pierucci (354-360).
This work discusses how it is possible to assess odour impact in presence of multiple similar sources by illustrating a case study. The study was conducted on an area of northern Italy comprising three small municipalities where four rendering plants are located near to each other. Based on the emission data resulting from olfactometric surveys conducted in different periods of the year the overall odour emission rate emitted by each plant were evaluated, showing that the major contributor to the odour impact on the territory was plant 2. These data were linked with meteorological and orographical data in order to evaluate odour dispersion with a model (Calpuff). The results of the odour dispersion modelling confirmed the outcomes of the olfactometric survey and they were further validated through a “questioning” survey, conducted with the aim of involving the population by means of questionnaires for reporting the perceived odour episodes, which showed a good correspondence (86.5%) between odour perceptions and simulated odour immissions.
Keywords: Odour episodes; Source identification; Odour sampling; Odour measurement; Rendering; Calpuff;

Aerosol speciation and mass prediction from toluene oxidation under high NOx conditions by Janya L. Kelly; Diane V. Michelangeli; Paul A. Makar; Donald R. Hastie; Michael Mozurkewich; Janeen Auld (361-369).
A kinetically based gas-particle partitioning box model is used to highlight the importance of parameter representation in the prediction of secondary organic aerosol (SOA) formation following the photo-oxidation of toluene. The model is initialized using experimental data from York University's indoor smog chamber and provides a prediction of the total aerosol yield and speciation. A series of model sensitivity experiments were performed to study the aerosol speciation and mass prediction under high NOx conditions (VOC/NOx = 0.2). Sensitivity experiments indicate vapour pressure estimation to be a large area of weakness in predicting aerosol mass, creating an average total error range of 70 μg m−3 (range of 5–145 μg m−3), using two different estimation methods. Aerosol speciation proved relatively insensitive to changes in vapour pressure. One species, 3-methyl-6-nitro-catechol, dominated the aerosol phase regardless of the vapour pressure parameterization used and comprised 73–88% of the aerosol by mass. The dominance is associated with the large concentration of 3-methyl-6-nitro-catechol in the gas-phase. The high NOx initial conditions of this study suggests that the predominance of 3-methyl-6-nitro-catechol likely results from the cresol-forming branch in the Master Chemical Mechanism taking a significant role in secondary organic aerosol formation under high NOx conditions. Further research into the yields and speciation leading to this reaction product is recommended.
Keywords: Toluene oxidation; Secondary organic aerosol; Aerosol modelling; Vapour pressure estimation;

Modelling the photochemical pollution over the metropolitan area of Porto Alegre, Brazil by C. Borrego; A. Monteiro; J. Ferreira; M.R. Moraes; A. Carvalho; I. Ribeiro; A.I. Miranda; D.M. Moreira (370-380).
The main purpose of this study is to evaluate the photochemical pollution over the Metropolitan Area of Porto Alegre (MAPA), Brazil, where high concentrations of ozone have been registered during the past years. Due to the restricted spatial coverage of the monitoring air quality network, a numerical modelling technique was selected and applied to this assessment exercise. Two different chemistry-transport models – CAMx and CALGRID – were applied for a summer period, driven by the MM5 meteorological model. The meteorological model performance was evaluated comparing its results to available monitoring data measured at the Porto Alegre airport. Validation results point out a good model performance. It was not possible to evaluate the chemistry models performance due to the lack of adequate monitoring data. Nevertheless, the model intercomparison between CAMx and CALGRID shows a similar behaviour in what concerns the simulation of nitrogen dioxide, but some discrepancies concerning ozone. Regarding the fulfilment of the Brazilian air quality targets, the simulated ozone concentrations surpass the legislated value in specific periods, mainly outside the urban area of Porto Alegre. The ozone formation is influenced by the emission of pollutants that act as precursors (like the nitrogen oxides emitted at Porto Alegre urban area and coming from a large refinery complex) and by the meteorological conditions.
Keywords: Air quality modelling; Ozone; CAMx; CALGRID; Porto Alegre – Brazil;

Significant geographic gradients in particulate sulfate over Japan determined from multiple-site measurements and a chemical transport model: Impacts of transboundary pollution from the Asian continent by Masahide Aikawa; Toshimasa Ohara; Takatoshi Hiraki; Okihiro Oishi; Akihiro Tsuji; Makiko Yamagami; Kentaro Murano; Hitoshi Mukai (381-391).
We found a significant geographic gradient (longitudinal and latitudinal) in the sulfate (SO4 2−) concentrations measured at multiple sites over the East Asian Pacific Rim region. Furthermore, the observed gradient was well reproduced by a regional chemical transport model. The observed and modeled SO4 2− concentrations were higher at the sites closer to the Asian continent. The concentrations of SO4 2− from China as calculated by the model also showed the fundamental features of the longitudinal/latitudinal gradient. The proportional contribution of Chinese SO4 2− to the total in Japan throughout the year was above 50–70% in the control case, using data for Chinese sulfur dioxide (SO2) emission from the Regional Emission Inventory in Asia (40–60% in the low Chinese emissions case, using Chinese SO2 emissions data from the State Environmental Protection Administration of China), with a winter maximum of approximately 65–80%, although the actual concentrations of SO4 2− from China were highest in summer. The multiple-site measurements and the model analysis strongly suggest that the SO4 2− concentrations in Japan were influenced by the outflow from the Asian continent, and this influence was greatest in the areas closer to the Asian continent. In contrast, we found no longitudinal/latitudinal gradient in SO2 concentrations; instead SO2 concentrations were significantly correlated with local SO2 emissions. Our results show that large amounts of particulate sulfate are transported over long distances from the East Asian Pacific Rim region, and consequently the SO4 2− concentrations in Japan are controlled by the transboundary outflow from the Asian continent.
Keywords: Filter-pack method; Sulfate; Sulfur dioxide; Transboundary pollution; East Asia;

A mathematical model to study the temporal dynamics of stable isotope 13C incorporation into monoterpene molecules, emitted from Mediterranean evergreen sclerophyll oak Quercus ilex L. leaves, was developed. The box model uses leaf level gas exchange and monoterpene emission data to assess biochemical and diffusional processes of the light-dependent monoterpene biosynthesis and emission within the leaf tissues. We estimated total leaf monoterpene pool exchange half-lifes against these processes. The slowest response took up to 38 h, while the fastest response occurred within 1 h, taking the sum of the lumped processes time constants into account. Separately, the turnover half-lives of the biochemical processes ranged between 26 min up to more than 4 h. The diffusional processes turnover times, driven by the physico-chemical properties of the monoterpene molecule, have been found to range between 32 min and 3 h, depending on the number of 13C-labeled carbon atoms. As a consequence, the steady-state assumption that is used in many larger scale emission models, may not hold in all cases and the application of process-based algorithms is beneficial to overcome such long transient pool dynamics of light-dependent monoterpene emission.
Keywords: Stable isotope; 13C; Mathematical model; Monoterpene emission; Temporal emission dynamics;

Air pollution from shipping is currently dominating the international and European agenda on environmental protection. Although port emissions are not significantly contributing to the overall picture of ship-generated emissions, it is important to note that the impact of ship exhaust pollutants has a direct effect on the human population and built environment of many urbanized ports. The passenger (main) port of Piraeus qualifies for a ship emission and externality study by virtue of its dominant presence in the Mediterranean expressed in terms of the most frequent port calls by coastal passenger ships and cruise ships operating in the region, as well as in terms of being a most crowded port city through hosting a sizeable resident and visiting (employers and otherwise) population over a relatively small area.An in-port ship activity-based methodology was applied for manoeuvring and berthing of coastal passenger ships and cruise ships calling at the passenger port of Piraeus, in order to estimate the emission of the main ship exhaust pollutants (NOX, SO2 and PM2.5) over a twelve-month period in 2008–2009. The estimated emissions were analyzed in terms of gas species, seasonality, activity and shipping sector. The application of external cost factors led to the estimation of the emission externalities, in an attempt to evaluate the economic impact of the damage emissions produce mainly upon the human population and the built environment.The results indicate that ship emissions in the passenger port of Piraeus reach 2600 tons annually and their estimated externalities over this period are around 51 million euro. Summer emissions and associated impacts are more profound and coastal passenger shipping, as opposed to cruise shipping, is the dominant contributor of emissions and associated externalities. Overall, in a port city such as Piraeus, the need to introduce stringent control on the emissions produced by passenger ships, beyond that dictated by the current 2005/33/EU Directive is very urgent.
Keywords: Port of Piraeus; Ship emissions; Emission externalities; Greek shipping;

We propose a method to evaluate the detection abilities of networks used for protection purposes. Such networks are designed for the detection of nuclear, biological or gaseous emissions, without constraint on the source location. Their assigned goal is to have the best chance to detect a threatening emission located anywhere in the vicinity of a domain to protect. Two sensors siting applications are addressed: sensors placed in the surroundings of a facility to protect, or sensors carried by people scattered within a small area. A network protection ability is related both to its detection scope, and to its response time. To assess the performance of such networks, two statistical indicators are therefore designed: the detection probability, computed on a large number of possible source locations, and the saturation time, which is the time when the maximum detection probability has been reached.Simulations are then carried out with the Polyphemus air quality modeling system for many emission scenarios, including 961 possible source locations, various emitted species, and a few representative meteorological situations. This allows to assess the performance of single sensors as well as full networks, and their sensitivity to parameters like meteorological conditions and source characteristics. The emitted quantity and meteorological dispersion are found to be important parameters, whereas the species type does not significantly influence the results. Two network design methods are considered: (1) networks composed of a given number of the “best” sensors according to an indicator, and (2) sensors placed in circles around the protected domain. The networks built with respect to the detection probability show good results with a limited number of sensors, while the saturation time is not reliable enough to build networks. The networks based on circles also show a good performance in the studied cases, provided there is a sufficient number of sensors.
Keywords: Detection network; Passive tracer; Polyphemus; Local scale; Regional scale;

Tropospheric ozone adversely affects human health and vegetation, and biogenic volatile organic compound (BVOC) emission has potential to influence ozone concentration in summer season. In this research, the standard emissions of isoprene and monoterpene from the vegetation of the Kinki region of Japan, estimated from growth chamber experiments, were converted into hourly emissions for July 2002 using the temperature and light intensity data obtained from results of MM5 meteorological model. To investigate the effect of BVOC emissions on ozone production, two ozone simulations for one-month period of July 2002 were carried out. In one simulation, hourly BVOC emissions were included (BIO), while in the other one, BVOC emissions were not considered (NOBIO). The quantitative analyses of the ozone results clearly indicate that the use of spatio-temporally varying BVOC emission improves the prediction of ozone concentration. The hourly differences of monthly-averaged ozone concentrations between BIO and NOBIO had the maximum value of 6 ppb at 1400 JST. The explicit difference appeared in urban area, though the place where the maximum difference occurred changed with time. Overall, BVOC emissions from the forest vegetation strongly affected the ozone generation in the urban area.
Keywords: Biogenic volatile organic compound; Ozone; MM5; CMAQ; Growth chamber;

This paper presents an objective methodology for determining the optimum number of ambient air quality stations in a monitoring network. The methodology integrates the multiple-criteria method with the spatial correlation technique. The pollutant concentration and population exposure data are used in this methodology in different ways. In the first stage, the Fuzzy Analytic Hierarchy Process (FAHP) with triangular fuzzy numbers (TFNs) is used to identify the most desirable monitoring locations. The network configuration is then determined on the basis of the concept of sphere of influences (SOIs). The SOIs are dictated by a predetermined cutoff value (r c) in the spatial correlation coefficients (r) between the pollutant concentrations at the monitoring stations identified from first step and the corresponding concentrations at neighboring locations in the region. Finally, the optimal station locations are ranked by using combined utility scores gained from the first and second steps. The expansion of air quality monitoring network of Riyadh city in Saudi Arabia is used as a case study to demonstrate the proposed methodology.
Keywords: Air quality monitoring network; Multiple-criteria Fuzzy Analytic Hierarchy Process; Triangular fuzzy numbers; Spatial correlation coefficients;