Atmospheric Environment (v.44, #4)
Editorial board (i).
Development of a GIS-based decision support system for urban air quality management in the city of Istanbul by Tolga Elbir; Nizamettin Mangir; Melik Kara; Sedef Simsir; Tuba Eren; Seda Ozdemir (441-454).
A decision support system has been developed for urban air quality management in the metropolitan area of Istanbul. The system is based on CALMET/CALPUFF dispersion modeling system, digital maps, and related databases to estimate the emissions and spatial distribution of air pollutants with the help of a GIS software. The system estimates ambient air pollution levels at high temporal and spatial resolutions and enables mapping of emissions and air quality levels. Mapping and scenario results can be compared with air quality limits. Impact assessment of air pollution abatement measures can also be carried out.
Keywords: Air quality management; Decision support system; Air quality modeling; Emission inventory; Geographical information system;
Ensemble and bias-correction techniques for air quality model forecasts of surface O3 and PM2.5 during the TEXAQS-II experiment of 2006 by I. Djalalova; J. Wilczak; S. McKeen; G. Grell; S. Peckham; M. Pagowski; L. DelleMonache; J. McQueen; Y. Tang; P. Lee; J. McHenry; W. Gong; V. Bouchet; R. Mathur (455-467).
Several air quality forecasting ensembles were created from seven models, running in real-time during the 2006 Texas Air Quality (TEXAQS-II) experiment. These multi-model ensembles incorporated a diverse set of meteorological models, chemical mechanisms, and emission inventories. Evaluation of individual model and ensemble forecasts of surface ozone and particulate matter (PM) was performed using data from 119 EPA AIRNow ozone sites and 38 PM sites during a 50-day period in August and September of 2006. From the original set of models, two new bias-corrected model data sets were built, either by applying a simple running mean average to the past 7 days of data or by a Kalman-Filter approach. From the original and two bias-corrected data sets, three ensembles were created by a simple averaging of the seven models. For further improvements three additional weighted model ensembles were created, where individual model weights were calculated using the singular value decomposition method. All six of the ensembles are compared to the individual models and to each other in terms of root mean square error, correlation, and contingency and probabilistic statistics. In most cases, each of the ensembles show improved skill compared to the best of the individual models. The over all best ensemble technique was found to be the combination of Kalman-Filtering and weighted averaging. PM2.5 aerosol ensembles demonstrated significant improvement gains, mostly because the original model's skill was very low.
Keywords: Air quality; Ozone; Particulate matter; TEXAQS 2006; Ensemble forecast;
Total OH reactivity and VOC analyses for gasoline vehicular exhaust with a chassis dynamometer by Yoshihiro Nakashima; Narumi Kamei; Shinji Kobayashi; Yoshizumi Kajii (468-475).
Total OH reactivity for the exhaust gas of gasoline vehicles was measured for the first time under nine different driving conditions with a chassis dynamometer at the National Institute for Environmental Studies (NIES). Along with the total OH reactivity measurements, analysis of trace species such as CH4, CO, NO, NO2, and 56 kinds of volatile organic compounds (VOCs), including two aldehydes, was carried out. The ratio of alkanes to alkenes in the exhaust gas turned out to depend on the condition of the driving cycles. There were a considerable number of unidentified peaks obtained during GC analysis. About 15–30% of the total carbon was unidentified species. The chemical compositions of vehicular exhaust were found to depend on the temperature of the engine or catalysts. The contribution of OH reactivity to the species obtained depended on the temperature condition for the engine. The calculated total OH reactivity for VOCs was compared with ozone formation potential (OFP) and it turned out that there are in good correlation, while the correlation for “Cold” start deviates from that for “Hot” start. The measured and calculated OH reactivities were compared with each other. For all driving cycles, the calculated OH reactivity was confirmed to be an underestimation, implying the existence of unknown species in the exhaust gas. The percentage contribution of OH reactivity to the unknown species during “Cold” start was about 17.5%, which was almost the same as that for “Hot” start at 17.0%. However, the absolute value of OH reactivity for “Cold” start was about ten times higher than that for “Hot” start.
Keywords: OH reactivity; Vehicular emission; Pump–probe laser induced fluorescence; Unknown species;
Uncertainty analysis of developed ANN and ANFIS models in prediction of carbon monoxide daily concentration by Roohollah Noori; Gholamali Hoshyaripour; Khosro Ashrafi; Babak Nadjar Araabi (476-482).
This study aims to predict daily carbon monoxide (CO) concentration in the atmosphere of Tehran by means of developed artificial neural network (ANN) and adaptive neuro-fuzzy inference system (ANFIS) models. Forward selection (FS) and Gamma test (GT) methods are used for selecting input variables and developing hybrid models with ANN and ANFIS. From 12 input candidates, 7 and 9 variables are selected using FS and GT, respectively. Evaluation of developed hybrid models and its comparison with ANN and ANFIS models fed with all input variables shows that both FS and GT techniques reduce not only the output error, but also computational cost due to less inputs. FS–ANN and FS–ANFIS models are selected as the best models considering R 2, mean absolute error and also developed discrepancy ratio statistics. It is also shown that these two models are superior in predicting pollution episodes. Finally, uncertainty analysis based on Monte-Carlo simulation is carried out for FS–ANN and FS–ANFIS models which shows that FS–ANN model has less uncertainty; i.e. it is the best model which forecasts satisfactorily the trends in daily CO concentration levels.
Keywords: Forward selection; Gamma test; Monte-Carlo; Episodes;
On-road traffic emissions in a megacity by Ariela D'Angiola; Laura E. Dawidowski; Darío R. Gómez; Mauricio Osses (483-493).
A new annual bottom–up emission inventory of criteria pollutants and greenhouse gases from on-road mobile sources was developed for 2006 for the metropolitan area of Buenos Aires, Argentina, within a four-year regional project aimed at providing tools for chemical weather forecast in South America. Under the scarcity of local emission factors, we collected data from measuring campaigns performed in Argentina, Brazil, Chile and Colombia and compiled a data set of regional emission factors representative of Latin American fleets and driving conditions. The estimated emissions were validated with respect to downscaled national estimates and the EDGAR global emission database. Our results highlight the role of older technologies accounting in average for almost 80% of the emissions of all species. The area exhibits higher specific emissions than developed countries, with figures two times higher for criteria pollutants. We analyzed the effect on emissions of replacing gasoline by compressed natural gas, occurring in Argentina since 1995. We identified (i) a relationship between number of vehicles and a compound socioeconomic indicator, and (ii) time-lags in vehicle technologies between developed and developing countries, which can be respectively applied for spatial disaggregation and the development of projections for other Latin American cities. The results may also be employed to complement global emission inventories and by local policy makers as an environmental management tool.
Keywords: Emission inventory; On-road transport; Latin America; Buenos Aires; Megacities; Regional emission factors;
Analysis of radon origin by backward atmospheric transport modelling by D. Arnold; A. Vargas; A.T. Vermeulen; B. Verheggen; P. Seibert (494-502).
This work shows how ambient radon concentrations measured at Cabauw station in central Netherlands are influenced by transport from different regions under typical transport conditions occurring during April and November, 2007 by means of atmospheric Lagrangian particle dispersion modelling in a receptor-oriented approach. Four specific regions have been isolated to assess their contribution to the modelled radon ambient concentrations at Cabauw, and two different radon flux assumptions. Westerly flows coming from the ocean are poor in radon and do not increase radon air concentrations unless there is some fetch over the British Isles. Continental transport, mainly from eastern and southern Europe, significantly increases radon background concentrations, reaching increments of 3 Bq m−3. A constant 0.66 atoms cm−2 s−1 radon flux over land and zero over water bodies is a good approximation for the source term in order to study regional contributions and modulation of the radon background.
Keywords: Cabauw; FLEXPART; Radon; Receptor-oriented modelling; Fetch analysis;
Aerosol properties, in-canopy gradients, turbulent fluxes and VOC concentrations at a pristine forest site in Amazonia by L.V. Rizzo; P. Artaxo; T. Karl; A.B. Guenther; J. Greenberg (503-511).
Aerosol physical and chemical properties were measured in a forest site in central Amazonia (Cuieiras reservation, 2.61S; 60.21W) during the dry season of 2004 (Aug–Oct). Aerosol light scattering and absorption, mass concentration, elemental composition and size distributions were measured at three tower levels (Ground: 2 m; Canopy: 28 m, and Top: 40 m). For the first time, simultaneous eddy covariance fluxes of fine mode particles and volatile organic compounds (VOC) were measured above the Amazonian forest canopy. Aerosol fluxes were measured by eddy covariance using a Condensation Particle Counter (CPC) and a sonic anemometer. VOC fluxes were measured by disjunct eddy covariance using a Proton Transfer Reaction Mass Spectrometer (PTR-MS). At nighttime, a strong vertical gradient of phosphorus and potassium in the aerosol coarse mode was observed, with higher concentrations at Ground level. This suggests a source of primary biogenic particles below the canopy. Equivalent black carbon measurements indicate the presence of light-absorbing aerosols from biogenic origin. Aerosol number size distributions typically consisted of superimposed Aitken (76 nm) and accumulation modes (144 nm), without clear events of new particle formation. Isoprene and monoterpene fluxes reached respectively 7.4 and 0.82 mg m−2 s−1 around noon. An average fine particle flux of 0.05 ± 0.10 106 m−2 s−1 was calculated, denoting an equilibrium between emission and deposition fluxes of fine mode particles at daytime. No significant correlations were found between VOC and fine mode aerosol concentrations or fluxes.
Keywords: Biogenic aerosols; VOC; Turbulent fluxes; Amazon;
Comparison of a two-dimensional numerical dust transport model with experimental dust emissions from soil surfaces in a wind tunnel by Jason A. Roney; Bruce R. White (512-522).
Near-surface wind-tunnel fugitive dust concentration profiles arising from soil surfaces beds were compared to a finite difference numerical dust transport model. Comparisons of the type shown in this study were previously non-existent in the literature due to the lack of experimental wind-tunnel data for near-surface concentrations over a soil bed. However, in a previous study by the authors, near-surface steady-state concentration profiles were measured in order to obtain fugitive dust emission rates, thus allowing the comparison to models shown in this paper. The novel aspects of the current study include: comparison of concentration profiles of dust obtained experimentally in the wind tunnel with those calculated numerically; comparison of the calculated numerical fetch effect on dust emissions with that obtained in the wind tunnel; and comparison of the emission rates calculated numerically with those obtained experimentally in the wind tunnel. Initial comparisons with the model indicate good agreement implying that the physical mechanism of advection–diffusion is reasonably modeled with the choice of equations for the simple “steady-state” process near the surface. Furthermore, the numerical solutions presented in this paper provide a means to systematically explore the relative impact of varied surface boundary conditions upon the emission process and provide a potential link between wind-tunnel simulations and field scale models.
Keywords: Particulate matter; Fugitive dust; Aerosols; Advection; Diffusion; Numerical model;
Improving ozone modeling in complex terrain at a fine grid resolution: Part I – examination of analysis nudging and all PBL schemes associated with LSMs in meteorological model by Yunhee Kim; Joshua S. Fu; Terry L. Miller (523-532).
Meteorological variables such as temperature, wind speed, wind directions, and Planetary Boundary Layer (PBL) heights have critical implications for air quality simulations. Sensitivity simulations with five different PBL schemes associated with three different Land Surface Models (LSMs) were conducted to examine the impact of meteorological variables on the predicted ozone concentrations using the Community Multiscale Air Quality (CMAQ) version 4.5 with local perspective. Additionally, the nudging analysis for winds was adopted with three different coefficients to improve the wind fields in the complex terrain at 4-km grid resolution. The simulations focus on complex terrain having valley and mountain areas at 4-km grid resolution. The ETA M–Y (Mellor–Yamada) and G–S (Gayno–Seaman) PBL schemes are identified as favorite options and promote O3 formation causing the higher temperature, slower winds, and lower mixing height among sensitivity simulations in the area of study. It is found that PX (Pleim–Xiu) simulation does not always give optimal meteorological model performance. We also note that the PBL scheme plays a more important role in predicting daily maximum 8-h O3 than land surface models. The results of nudging analysis for winds with three different increased coefficients' values (2.5, 4.5, and 6.0 × 10−4 s−1) over seven sensitivity simulations show that the meteorological model performance was enhanced due to improved wind fields, indicating the FDDA nudging analysis can improve model performance considerably at 4-km grid resolution. Specifically, the sensitivity simulations with the coefficient value (6.0 × 10−4) yielded more substantial improvements than with the other values (2.5 and 4.5 × 10−4). Hence, choosing the nudging coefficient of 6.0 × 10−4 s−1 for winds in MM5 may be the best choice to improve wind fields as an input, as well as, better model performance of CMAQ in the complex terrain area. As a result, a finer grid resolution is necessary to evaluate and access of CMAQ results for giving a detailed representation of meteorological and chemical processes in the regulatory modeling. A recommendation of optimal scheme options for simulating meteorological variables in the complex terrain area is made.
Keywords: Model performance; CMAQ; Planetary boundary layer; Land surface model; Nudging analysis;
Ultrafine particles at three different sampling locations in Taiwan by Sheng-Chieh Chen; Chuen-Jinn Tsai; Charles C.-K. Chou; Gwo-Dong Roam; Sen-Sung Cheng; Ya-Nan Wang (533-540).
Atmospheric ultrafine particles (UPs or PM0.1) were investigated at the roadside of Syuefu road in Hsinchu city, in the Syueshan highway tunnel in Taipei and in the NTU Experimental Forest in Nantou, Taiwan. A SMPS (TSI 3936) and three MOUDIs (MSP 110) were collocated to determine the number and mass concentrations of the PM0.1 simultaneously. The filter samples were further analyzed for organic carbon (OC), element carbon (EC), water-soluble ions and trace elements. Taking into account the OC artifact of PM0.1, good chemical mass closure (ratio of the reconstructed chemical mass to the gravimetrical mass of PMs) was obtained with an unknown percentage of 10.6, 26.2 and 37.2% at the roadside, tunnel and forest, respectively. The unexplained mass was attributed to aerosol water in this study. The artifact at the roadside, tunnel and the forest PM0.1 mass was found to be as high as 51.6 ± 10.7%, 20.0 ± 5.4% and 85.6 ± 18.4%, respectively. Finally, the effective density of the roadside, tunnel and forest PM0.1 was calculated based on the results of chemical speciation and found to be 1.45, 1.29 and 1.22 g cm−3, respectively, which was in good agreement with that obtained by using the method of . Based on these results, it is foreseeable that the number concentration of the SMPS can be converted using the effective density determined by for the real time measurement of the PM0.1 concentration.
Keywords: Atmospheric aerosol; Ultrafine particle; Artifact of organic carbon; Chemical mass closure; Particle effective density;
Characterization of colored products formed during irradiation of aqueous solutions containing H2O2 and phenolic compounds by Jonathan L. Chang; Jonathan E. Thompson (541-551).
Irradiation of aqueous (pH = 5) mixtures containing hydrogen peroxide (1 mM) and phenolic compounds (10 mM) were found to produce visible light absorbing solutions over the course of several hours. The kinetics and products of these reactions were studied by UV–VIS absorbance, electrospray mass spectrometry, FTIR, fluorescence, and NMR and compared to humic-like substances commonly found in atmospheric particulate matter. It was determined the reactions leading to formation of color are quite general to this compound class, and the reactions proceeded more rapidly with hydroxyl or methoxy substitution ortho to the phenolic OH. However, para substitution generally slowed formation of colored compounds compared to the unsubstituted form. Mass spectrometry confirms compounds of several hundred Da formed in the reaction mixtures. The IR spectra of the reaction products bear similarity to that observed for authentic aerosol humic-like substances. The results indicate radical coupling of phenols and methoxylated phenols in tropospheric waters may contribute to humic-like particulate matter.
Keywords: OH radical; Light absorbing carbon; Brown carbon; Humic-like substances (HULIS); Airborne particulate matter;
Influence of regional development policies and clean technology adoption on future air pollution exposure by Mark Hixson; Abdullah Mahmud; Jianlin Hu; Song Bai; Debbie A. Niemeier; Susan L. Handy; Shengyi Gao; Jay R. Lund; Dana Coe Sullivan; Michael J. Kleeman (552-562).
Future air pollution emissions in the year 2030 were estimated for the San Joaquin Valley (SJV) in central California using a combined system of land use, mobile, off-road, stationary, area, and biogenic emissions models. Four scenarios were developed that use different assumptions about the density of development and level of investment in transportation infrastructure to accommodate the expected doubling of the SJV population in the next 20 years. Scenario 1 reflects current land-use patterns and infrastructure while scenario 2 encouraged compact urban footprints including redevelopment of existing urban centers and investments in transit. Scenario 3 allowed sprawling development in the SJV with reduced population density in existing urban centers and construction of all planned freeways. Scenario 4 followed currently adopted land use and transportation plans for the SJV. The air quality resulting from these urban development scenarios was evaluated using meteorology from a winter stagnation event that occurred on December 15th, 2000 to January 7th 2001. Predicted base-case PM2.5 mass concentrations within the region exceeded 35 μg m−3 over the 22-day episode. Compact growth reduced the PM2.5 concentrations by ∼1 μg m−3 relative to the base-case over most of the SJV with the exception of increases (∼1 μg m−3) in urban centers driven by increased concentrations of elemental carbon (EC) and organic carbon (OC). Low-density development increased the PM2.5 concentrations by 1–4 μg m−3 over most of the region, with decreases (0.5–2 μg m−3) around urban areas. Population-weighted average PM2.5 concentrations were very similar for all development scenarios ranging between 16 and 17.4 μg m−3. Exposure to primary PM components such as EC and OC increased 10–15% for high density development scenarios and decreased by 11–19% for low-density scenarios. Patterns for secondary PM components such as nitrate and ammonium ion were almost exactly reversed, with a 10% increase under low-density development and a 5% decrease under high density development. The increased human exposure to primary pollutants such as EC and OC could be predicted using a simplified analysis of population-weighted primary emissions. Regional planning agencies should develop thresholds of population-weighted primary emissions exposure to guide the development of growth plans. This metric will allow them to actively reduce the potential negative impacts of compact growth while preserving the benefits.
Keywords: San Joaquin Valley; Smart growth; UCD source-oriented air quality model;
A cluster analysis of long range air transport pathways and associated pollutant concentrations within the UK by Jacob Baker (563-571).
A cluster analysis of four-day back trajectories for January 1998 to December 2001 arriving mid-afternoon in Birmingham, UK at three different within boundary layer arrival heights has been performed in order for a better understanding of the pollution meteorology influencing this region. The time period was purposely chosen to encompass the Pollution in the Urban Midlands Atmosphere field campaign. Six natural synoptic scale transport patterns were identified with three, strong-westerly, westerly and slow-easterly, showing seasonal variation in frequency. Significant differences in air pollutant concentrations and behaviour were found between air mass cluster types when they were analysed with measurements taken from an urban background site in Birmingham and a rural site in Harwell. Highest concentrations of primary pollutants were associated with a slow-easterly air mass from mainland Europe, while lowest concentrations were associated with south-westerly and strong-westerly air masses passing over the Atlantic Ocean. The polluted slow-easterly air mass was associated with highest ozone concentration for the warm season and lowest ozone concentration for the cool season. This could be explained by photochemical ozone production during the warm season and NOx titration of background ozone during the cool season, when photochemically “inactive” conditions prevailed. A wealth of information was determinable, including influences of short and long-range transport and photochemical productivity.
Keywords: Cluster analysis; Air pollution; Trajectory sets; Ozone; Midlands;
South Pole Antarctica observations and modeling results: New insights on HOx radical and sulfur chemistry by Roy Mauldin; Edward Kosciuch; Fred Eisele; Greg Huey; David Tanner; Steve Sjostedt; Don Blake; Gao Chen; Jim Crawford; Douglas Davis (572-581).
Measurements of OH, H2SO4, and MSA at South Pole (SP) Antarctica were recorded as a part of the 2003 Antarctic Chemistry Investigation (ANTCI 2003). The time period 22 November, 2003–2 January, 2004 provided a unique opportunity to observe atmospheric chemistry at SP under both natural conditions as well as those uniquely defined by a solar eclipse event. Results under natural solar conditions generally confirmed those reported previously in the year 2000. In both years the major chemical driver leading to large scale fluctuations in OH was shifts in the concentration levels of NO. Like in 2000, however, the 2003 observational data were systematically lower than model predictions. This can be interpreted as indicating that the model mechanism is still missing a significant HOx sink reaction(s); or, alternatively, that the OH calibration source may have problems. Still a final possibility could involve the integrity of the OH sampling scheme which involved a fixed building site. As expected, during the peak in the solar eclipse both NO and OH showed large decreases in their respective concentrations. Interestingly, the observational OH profile could only be approximated by the model mechanism upon adding an additional HOx radical source in the form of snow emissions of CH2O and/or H2O2. This would lead one to think that either CH2O and/or H2O2 snow emissions represent a significant HOx radical source under summertime conditions at SP. Observations of H2SO4 and MSA revealed both species to be present at very low concentrations (e.g., 5 × 105 and 1 × 105 molec cm−3, respectively), but similar to those reported in 2000. The first measurements of SO2 at SP demonstrated a close coupling with the oxidation product H2SO4. The observed low concentrations of MSA appear to be counter to the most recent thinking by glacio-chemists who have suggested that the plateau's lower atmosphere should have elevated levels of MSA. We speculate here that the absence of MSA may reflect efficient atmospheric removal mechanisms for this species involving either dynamical and/or chemical processes.
Keywords: OH; H2SO4; MSA; Hydroxyl; Sulfuric; ANTCI; Pole; Antarctic; Oxidation; SO2;
Atmospherically deposited major and trace elements in the winter snowpack along a gradient of altitude in the Central Pyrenees: The seasonal record of long-range fluxes over SW Europe by Montserrat Bacardit; Lluís Camarero (582-595).
The chemistry of high mountain snowpacks is a result of the long-range atmospheric transport and deposition of elements. Pyrenean snowpacks contain information about the fluxes of elements over SW Europe in winter. Here we analysed Al, Ti, Mn, Fe, Ni, Cu, Zn, As, Se, Cd and Pb in the 2004–05 winter snowpack in the Central Pyrenees, at an altitude range of 1820–3200 m a.s.l. Ni, As, Se and Cd were not detected in most cases. The concentrations of the remaining elements were comparable to those found in other high mountain areas in Europe and North America considered representative of regional background of atmospheric deposition in populated areas. In contrast, our measurements were higher than those of polar areas, which represent the global background. Single measurements of concentrations and snow accumulation were subject to considerable spatial variability, which may be attributable to strong wind drift and other post-depositional processes. The major ions chemistry of the snow indicated three possible origins for the solutes: terrigenous dust, sea salt spray and polluting S and N aerosols. We found no association between Cu, Zn and Pb and any of these possible sources. This observation therefore indicates that these elements were not preferentially bound to any particular kind of aerosol. Snow collected at altitudes of up to 2050 m a.s.l. presented higher concentrations of several elements than snow above this altitude, thereby indicating a local influence. Snow collected above 2300 m a.s.l. was therefore more representative of broad regional inputs. At these higher altitudes, snow was not enriched in Al, Ti, Mn, Fe or As compared with the composition of the upper continental crust and the local lithology, and these elements (except Mn) appeared almost exclusively in the particulate fraction. This observation indicates that Al, Ti, Mn, Fe and As were present mainly as part of dust particles of terrigenous origin. In contrast, Cu, Zn, and Pb presented medium to high enrichment factors and showed a higher proportion of soluble forms, thereby indicating their polluting character.
Keywords: Major and trace elements; Long-range pollution; Snowpack; High mountain; Pyrenees;