Atmospheric Environment (v.41, #9)
Editorial board (i).
Estimating the effects of increased urbanization on surface meteorology and ozone concentrations in the New York City metropolitan region by Kevin Civerolo; Christian Hogrefe; Barry Lynn; Joyce Rosenthal; Jia-Yeong Ku; William Solecki; Jennifer Cox; Christopher Small; Cynthia Rosenzweig; Richard Goldberg; Kim Knowlton; Patrick Kinney (1803-1818).
Land use and pollutant emission changes can have significant impacts on air quality, regional climate, and human health. Here we describe a modeling study aimed at quantifying the potential effects of extensive changes in urban land cover in the New York City (NYC), USA metropolitan region on surface meteorology and ozone (O3) concentrations. The SLEUTH land-use change model was used to extrapolate urban land cover over this region from “present-day” (ca. 1990) conditions to a future year (ca. 2050), and these projections were subsequently integrated into meteorological and air quality simulations. The development of the future-year land-use scenario followed the narrative of the “A2” scenario described by the Intergovernmental Panel on Climate Change (IPCC), but was restricted to the greater NYC area. The modeling system consists of the Penn State/NCAR MM5 mesoscale meteorological model; the Sparse Matrix Operator Kernal Emissions processing system; and the US EPA Community Multiscale Air Quality model, and simulations were performed for two 18-day episodes, one near-past and one future. Our results suggest that extensive urban growth in the NYC metropolitan area has the potential to increase afternoon near-surface temperatures by more than 0.6 °C and planetary boundary layer (PBL) heights by more than 150 m, as well as decrease water vapor mixing ratio by more than 0.6 g kg−1, across the NYC metropolitan area, with the areal extent of all of these changes generally coinciding with the area of increased urbanization. On the other hand, the impacts of these land use changes on ozone concentrations are more complex. Simulation results indicate that future changes in urbanization, with emissions held constant, may lead to increases in episode-average O3 levels by about 1–5 ppb, and episode-maximum 8 h O3 levels by more than 6 ppb across much of the NYC area. However, spatial patterns of ozone changes are heterogeneous and also indicate the presence of areas with decreasing ozone concentrations. When anthropogenic emissions were increased to be consistent with the extensive urbanization in the greater NYC area, the O3 levels increased in outer counties of the metropolitan region but decreased in others, including coastal Connecticut and the Long Island Sound area.
Keywords: Models-3/CMAQ; MM5; Air pollution meteorology; O3; Land use change;
Characteristics of carbonyl compounds in public vehicles of Beijing city: Concentrations, sources, and personal exposures by Xiaobing Pang; Yujing Mu (1819-1824).
The characteristics of carbonyl compounds (carbonyls) including concentrations, major sources, and personal exposure were investigated for 29 vehicles including taxi, bus and subway in Beijing. It was found that the taxis (Xiali, TA) and buses (Huanghe, BA) fueled by gasoline with longer service years had the higher indoor carbonyl levels (178±42.7 and 188±31.6 μg m−3) while subways energized by electricity without exhaust and the jingwa buses (BB) driven in the suburb had the lower levels with total concentrations of 98.5±26.3 and 92.1±20.3 μg m−3, respectively. Outdoor carbonyls of taxi cars and buses were nearly at the same level with their total concentrations varying from 80 to 110 μg m−3. The level of outdoor subways carbonyls was equal with the ambient air levels. Exhaust leakage, indoor material emissions, photochemical formation, and infiltration of outdoor air were considered to be the major sources to in-vehicle carbonyls. Personal exposures and cancer risk to formaldehyde and acetaldehyde were calculated for professional bus and taxi drivers, respectively. Taxi drivers had the highest cancer risk with personal exposure to formaldehyde and acetaldehyde of 212 and 243 μg day−1, respectively. The public concern should pay considerable attention to professional drivers’ health.
Keywords: Carbonyl compounds; Public vehicle; Personal exposure;
Detection and quantification of 2-methyltetrols in ambient aerosol in the southeastern United States by Andrea L. Clements; John H. Seinfeld (1825-1830).
Filters collected from the Southeastern Aerosol Research and Characterization (SEARCH) air monitoring network were analyzed for the presence of 2-methyltetrols, namely 2-methylthreitol and 2-methylerythritol, two compounds that are products of the photooxidation of isoprene and have been detected in aerosol at a variety of sites around the globe. The 2-methytetrols were detected in ambient filter samples collected at the four SEARCH sites, Birmingham, AL, Centreville, AL, Pensacola, FL, and at Jefferson Street in Atlanta, GA, in late June 2004. Average atmospheric concentrations of 11.9 and 4.8 ng m−3 were measured for 2-methylerythritol and 2-methylthreitol, respectively, at the inland sampling sites, whereas average concentrations of 4.9 and 1.6 ng m−3 were measured at the coastal sampling location (Pensacola). On average, the aerosol loading from these two compounds accounts for approximately 0.42% and 0.21% of the organic mass collected on a given sampling day at the inland and coastal sites, respectively. The present data on these compounds, which are particulate-phase fingerprints of isoprene photooxidation, add to the growing body of ambient data on secondary organic aerosol from isoprene.
Keywords: 2-Methyltetrols; 2-Methylthreitol; 2-Methylerythritol; Isoprene; Secondary organic aerosol;
Spatial distribution of source locations for particulate nitrate and sulfate in the upper-midwestern United States by Weixiang Zhao; Philip K. Hopke; Liming Zhou (1831-1847).
Two back-trajectory analysis methods designed to be used with multiple site data, simplified quantitative transport bias analysis (SQTBA) and residence time weighted concentration (RTWC), were applied to nitrate and sulfate concentration data from two rural sites (the Mammoth Cave National Park and the Great Smoky Mountain National Park) and five urban sites (Chicago, Cleveland, Detroit, Indianapolis, and St. Louis) for an intensive investigation on the spatial patterns of origins for these two species in the upper-midwestern area. The study was made by dividing the data into five categories: all sites and all seasons, rural sites in summer, rural sites in winter, urban sites in summer, and urban sites in winter. A general conclusion was that the origins of the nitrate in these seven sites were mainly in the upper-midwestern areas, while the sulfate in these seven sites were mainly from the Ohio and Tennessee River Valley areas. The upper-midwestern areas are regions of high ammonia emissions rather than high NO x emissions. In the winter, metropolitan areas showed the highest nitrate emission potential suggesting the importance of local NO x emissions. In the summer, ammonia emissions from fertilizer application in the lower midwestern area made a significant contribution to nitrate in the rural sites of this study. The impact of the wind direction prevalence on the source spatial patterns was observed by comparing the urban and rural patterns of the summer. The differences between the results of two methods are discussed and suggestions for applying these methods are also provided.
Keywords: SQTBA; RTWC; Back trajectory; Nitrate; Sulfate; Trajectory ensemble methods;
VOC concentration profiles in an ozone non-attainment area: A case study in an urban and industrial complex metroplex in southern Taiwan by Chiang Hung-Lung; Tsai Jiun-Horng; Chen Shih-Yu; Lin Kuo-Hsiung; Ma Sen-Yi (1848-1860).
VOCs are important precursors of the atmospheric ozone formation species. This study investigated the airborne concentrations of 52 VOCs at two air quality monitoring stations, Daliao and Tzouying, during wintertime in southern Taiwan. Airborne VOCs samples were taken in stainless steel canisters four times per day and analyzed via gas chromatography/mass spectrometry. Maximum increment reactivity (MIR) was used to evaluate the ozone formation potential in this ozone non-attainment region. Toluene, propane, isopentane, propene, n-butane, n-pentane and isoprene contributed 78–79% of the 52 VOCs in Daliao. Toluene, 1-butene, isopentane, propene, propane, n-undecane, and n-butane contributed 71–77% of the 52 VOCs in Tzouying. The VOCs concentrations were higher in Daliao due to the high toluene emissions from a paint plant and a solvent plant in the nearby industrial district. The 24-h VOC concentrations averaged 25 ppb higher in Tzouying than in Daliao. The ozone formation potential of airborne VOCs was 1687–2730 and 1717–2261 μg-O3/g-VOCs in Daliao and Tzouying, respectively. Ozone concentrations in Tzouying were 44 ppb higher than in Daliao during the 1200–1600 sampling period.
Keywords: Volatile organic compounds (VOCs); Maximum increment reactivity (MIR); Ozone;
Atmospheric mercury in the Great Smoky Mountains compared to regional and global levels by Ralph J. Valente; Catherine Shea; K. Lynn Humes; Roger L. Tanner (1861-1873).
Improvements in measurement technology are permitting development of a more detailed scientific understanding of the cycling of mercury in the global atmospheric environment. Critical to advancing the state of knowledge is the acquisition of accurate measurement of speciated mercury (gaseous and particulate) at ground research stations in a variety of settings located around the globe. This paper describes one such research effort conducted at TVA's Look Rock air quality monitoring site in Tennessee—a mountain top site (813 m elevation) just west of the Great Smoky Mountains National Park. The Great Smoky Mountains National Park is the largest National Park in the eastern US and it receives environmental protection under a variety of US statutes. Gaseous and particle mercury species along with some additional trace gases were measured at Look Rock during two field studies totaling 84 days in the spring and summer of 2004. Average results for the entire sampling period are: gaseous elemental mercury Hg(0): 1.65 ng m−3, reactive gaseous mercury RGM: 0.005 ng m−3, particulate mercury Hg(p): 0.007 ng m−3. Literature review indicates that these levels are within the range found for other rural/remote sites in North America and worldwide. Reactive and particulate mercury comprised together less than 1%, on average, of total airborne mercury at Look Rock. When compared to the global background mercury literature, the Look Rock measurements demonstrate that the atmospheric mercury levels in the vicinity of the Great Smoky Mountains National Park are clearly dominated by the global atmospheric pool, not by local or regional sources.
Keywords: Meteorology; Gaseous elemental mercury; Reactive gaseous mercury; Particle mercury; Fine particulate mercury; Global mercury; Tekran; Mercury speciation; Great Smoky Mountains; Atmospheric mercury;
Controlled generation of black carbon particles from a diffusion flame and applications in evaluating black carbon measurement methods by Thomas W. Kirchstetter; T. Novakov (1874-1888).
Measurements of black carbon (BC) concentration have long been uncertain. Neither a BC standard or a technique that provides a reliable measurement of BC exist, which precludes the evaluation and optimization of BC measurement methods. In this manuscript, we describe the generation of BC particles (mass absorption efficiency ∼8.5 m2 g−1 and single scattering albedo ∼0.2 at 530 nm) using an inverted diffusion flame. This flame is remarkably stable and can be used to generate a wide range of nearly constant concentrations of BC particles for many (e.g., 10+) hours. The particles contain essentially no organic carbon (OC), so the quantification of BC mass using any of the thermal or thermal–optical analysis (TOA) methods is straightforward instead of highly uncertain. In this case, the TOA measurement of BC can be used to evaluate the accuracy of other BC measurement methods. In this paper, we demonstrate the application of the diffusion flame in evaluating BC measurements made with filter-based light transmission methods, and in particular the aethalometer. We show that the amount of light attenuated by a BC-laden filter increases in less than constant proportion to the BC mass loading, and thus the effective BC attenuation coefficient decreases with increased BC mass loading. When sampling BC at constant concentration, the aethalometer erroneously reports decreasing concentrations of BC as its filter becomes increasingly loaded because it treats the attenuation coefficient as a constant. A simple method to correct erroneous aethalometer data when sampling aerosols with low single scattering albedo is presented. Another application of the diffusion flame considered in this paper is the development of BC standards for TOA. We envision the preparation of filter samples with known amounts of BC mixed with other aerosol constituents, which may help in understanding the uncertainty in and optimizing TOA measurements, and may be of use in future TOA method comparison studies. Toward this end, we demonstrate that the diffusion flame can be used to replicate filter samples with known amounts of BC. Additionally, we show that the combustion temperature of BC during TOA depends on sample composition, which suggests that the temperature-defined carbon fractions of some thermal and TOA methods may be of limited value.
Keywords: Carbonaceous aerosol; Black carbon; Elemental and organic carbon; Thermal–optical analysis; Aethalometer; Particle soot absorption photometer;
Contribution to ambient benzene concentrations in the vicinity of petrol stations: Estimation of the associated health risk by Spyros P. Karakitsios; Vasileios K. Delis; Pavlos A. Kassomenos; Georgios A. Pilidis (1889-1902).
This work examines the contribution of petrol stations to the ambient benzene concentrations and attempts to estimate the possible health risks for the people living in the vicinity of such installations.Three monitoring sites (urban, suburban and rural) were used as reference points and the benzene concentrations were recorded at several distances along their perimeter.In order to evaluate the net contribution of the petrol station to the ambient benzene concentrations, the urban background concentration, measured by passive samplers and the contribution of the roads, estimated with both the COPERT and the linear source model CALINE 4, were deduced. Validation and optimization of the modeling system COPERT and CALINE4 was done in advance to ensure the reliability of the results. It seems that petrol stations have a significant contribution to ambient benzene concentrations in their vicinity.Finally, a risk assessment evaluation was attempted in terms of increased cancer risk due to the presence of the petrol stations in an area. The results show remarkable increase of the population risks in the vicinity, ranging from 3% to 21% in comparison to the population in the rest of the town.
Keywords: Benzene; Petrol stations; Benzene modeling; Benzene risk evaluation;
Evaluation of formation rates of NO2 to gaseous and particulate nitrate in the urban atmosphere by Y-C. Lin; M-T. Cheng (1903-1910).
This work investigates the formation rates of gaseous and particulate nitrate in an urban atmosphere. This investigation is based on theoretical evaluations regarding potential NO2 oxidant reactions, leading to calculated values compared with field observations in Taichung City, Taiwan in 2002. The results show that the correlation coefficient (r) between the calculated value and field observation for HNO3 was 0.83 and that for NO 3 - was 0.66, suggesting that the theoretical calculations are suitable for assessing the formation rate of nitrate species. The 12-h average conversion rate of NO2 to HNO3 was approximately 3.4±3.1% h−1, while the formation rate of particulate NO 3 - was 2.4±1.8% h−1. Seasonal variations in gaseous and particulate production rates were obtained. The formation rate of HNO3 was found to be higher in summer, whereas the NO 3 - rate was lowest. The factors affecting the formation rate were also investigated using the model sensitivity test. The results showed that both HNO3 and NO 3 - were significantly dependent upon the ambient temperature and relative humidity in a moist atmosphere.
Keywords: Formation rate; Gaseous nitrate; Particulate nitrate; NO2 oxidant reactions; Temperature; Relative humidity;
Temporal variability of mercury speciation in urban air by Bian Liu; Gerald J. Keeler; J. Timothy Dvonch; James A. Barres; Mary M. Lynam; Frank J. Marsik; Joy Taylor Morgan (1911-1923).
Semi-continuous measurements of ambient mercury (Hg) species were performed in Detroit, MI, USA for the calendar year 2003. The mean (±standard deviation) concentrations for gaseous elemental mercury (GEM), particulate mercury (HgP), and reactive gaseous mercury (RGM) were 2.2±1.3 ng m−3, 20.8±30.0, and 17.7±28.9 pg m−3, respectively. A clear seasonality in Hg speciation was observed with GEM and RGM concentrations significantly (p<0.001) greater in warm seasons, while HgP concentrations were greater in cold seasons. The three measured Hg species also exhibited clear diurnal trends which were particularly evident during the summer months. Higher RGM concentrations were observed during the day than at night. Hourly HgP and GEM concentrations exhibited a similar diurnal pattern with both being inversely correlated with RGM. Multivariate analysis coupled with conditional probability function analysis revealed the conditions associated with high Hg concentration episodes, and identified the inter-correlations between speciated Hg concentrations, three common urban air pollutants (sulfur dioxide, ozone, and nitric oxides), and meteorological parameters. This analysis suggests that both local and regional sources were major factors contributing to the observed temporal variations in Hg speciation. Boundary layer dynamics and the seasonal meteorological conditions, including temperature and moisture content, were also important factors affecting Hg variability.
Keywords: Gaseous elemental mercury; Reactive gaseous mercury; Particulate mercury; Mercury sources;
Properties of organic matter in PM2.5 at Changdao Island, China—A rural site in the transport path of the Asian continental outflow by Jialiang Feng; Zhigang Guo; Chak K. Chan; Ming Fang (1924-1935).
Fifty-five seasonal PM2.5 samples were collected March 2003–January 2004 at Changdao, a resort island located at the demarcation line between Bohai Sea and Yellow Sea in Northern China. Changdao is in the transport path of the continental aerosols heading toward the Pacific Ocean in winter and spring due to the East Asia Monsoon. Solvent-extractable organic compounds (SEOC), organic carbon (OC), elemental carbon (EC) and water-soluble organic carbon (WSOC) were analyzed for source identification based on molecular markers. This data set provides useful information for the downstream site researchers of the Asian continental outflow. Total carbon (TC, OC+EC) was ∼18 μg m−3 in winter, ∼9 μg m−3 in spring and autumn and a large part of the TC was WSOC (33% in winter, >45% in the other seasons). Winter and spring were the high SEOC seasons with n-fatty acids the highest at ∼290 and ∼170 ng m−3, respectively, followed by n-alkanes at ∼210 and ∼90 ng m−3, and polycyclic aromatic hydrocarbons (PAHs) were also at high at ∼120 and ∼30 ng m−3. High WSOC/TC, low C18:1/C18 of fatty acids, and low concentrations of labile PAHs such as benzo(a)pyrene, together with back trajectory analysis suggested that the aerosols were aged and transported. PAHs, triterpane and sterane distributions provided evidence that coal burning was the main source of the continental outflow. The detection of levoglucosan and β-sitosterol in nearly all the samples showed the impact of biomass burning.
Keywords: PM2.5; SEOC; OC/EC; WSOC; GC-MS; Transport; Changdao; China;
The continuous field measurements of soluble aerosol compositions at the Taipei Aerosol Supersite, Taiwan by Shih-Yu Chang; Chung-Te Lee; Charles C.-K. Chou; Shaw-Chen Liu; Tian-Xue Wen (1936-1949).
The characteristics of ambient aerosols, affected by solar radiation, relative humidity, wind speed, wind direction, and gas–aerosol interaction, changed rapidly at different spatial and temporal scales. In Taipei Basin, dense traffic emissions and sufficient solar radiation for typical summer days favored the formation of secondary aerosols. In winter, the air quality in Taipei Basin was usually affected by the Asian continental outflows due to the long-range transport of pollutants carried by the winter monsoon. The conventional filter-based method needs a long time for collecting aerosols and analyzing compositions, which cannot provide high time-resolution data to investigate aerosol sources, atmospheric transformation processes, and health effects. In this work, the in situ ion chromatograph (IC) system was developed to provide 15-min time-resolution data of nine soluble inorganic species (Cl−, NO2 −, NO3 −, SO4 2−, Na+, NH4 +, K+, Mg2+ and Ca2+). Over 89% of all particles larger than approximately 0.056 μm were collected by the in situ IC system. The in situ IC system is estimated to have a limit of detection lower than 0.3 μg m−3 for the various ambient ionic components. Depending on the hourly measurements, the pollutant events with high aerosol concentrations in Taipei Basin were associated with the local traffic emission in rush hour, the accumulation of pollutants in the stagnant atmosphere, the emission of industrial pollutants from the nearby factories, the photochemical secondary aerosol formation, and the long-range transport of pollutants from Asian outflows.
Keywords: In situ IC; Chemical analysis; Soluble ions; Continuous analysis; Local pollutant; Long-range transport;
Separate chemical characterizations of fog water, aerosol, and gas before, during, and after fog events near an industrialized area in Japan by Masahide Aikawa; Takatoshi Hiraki; Motoharu Suzuki; Motonori Tamaki; Mikio Kasahara (1950-1959).
Fog water, aerosol, and gas were separately collected at Mt. Rokko (altitude 931 m) in Kobe, Japan, using a new sampling method at a mountainous site near a highly industrialized area. The fog water was collected by an active string-fog collector and the aerosol and gas by using the filter pack method. Using plural filter packs and controlling or switching the airflow before, during, and after a fog event made it possible to collect the fog water, aerosol, and gas separately. Nitrate species such as NO3 −(p) and HNO3(g) were effectively scavenged by fog water, while sulfur species such as SO4 2−(p) and SO2(g) could not be easily and effectively scavenged because of the poor solubility of SO2(g). This difficulty was experimentally examined through an in situ investigation. Ion species (especially Na+(p) and Ca2+(p)) which form coarse particles were easily and effectively scavenged by fog water. On the other hand, the difficulty of scavenging Mg2+(p) could not be explained by particle size.
Keywords: Fog water; Aerosol; Gas; Separate collection;
What are the sources and conditions responsible for exceedences of the 24 h PM10 limit value (50 μg m−3) at a heavily trafficked London site? by Aurélie Charron; Roy M. Harrison; Paul Quincey (1960-1975).
The European Union has set limit values for PM10 to be met in 2005. At Marylebone Road, London, where the traffic is heavy, the daily limit value of 50 μg m−3 is exceeded more than 35 times a year. A total of 185 days with daily PM10 concentrations exceeding the limit value of 50 μg m−3 measured between January 2002 and December 2004 (data capture of 89.5%) are discussed in this paper. These exceedences were more frequent in early spring and in autumn. Concentrations have been disaggregated into regional, urban (background) and local (street) contributions. Most of the episodes of gravimetric PM10 above the limit value were associated with a high regional background and very often the regional contribution dominated the PM10 mass. The secondary aerosol (especially the particulate nitrate) made a major contribution to the PM10 load. These situations were frequently observed when air masses came from the European mainland (showing that both emissions from the UK and other EU countries contributed to the exceedences), and less frequently with maritime air masses that have stagnated over the UK (showing that emissions from the UK alone less frequently contributed to the high regional background). However, the higher frequency of episodes breaching the limit value at the roadside site than at the rural site and the higher frequency of PM10 concentrations above the limit value on weekdays show that the high regional contributions are additional to local and urban emissions. Local emissions mainly due to traffic were the second important contributor to the exceedences, while the contribution of the urban background of London was less important than the local emissions and the regional background. Applying the pragmatic mass closure model of Harrison et al. [2003. A pragmatic mass closure model for airborne particulate matter at urban background and roadside sites. Atmospheric Environment 37, 4927–4933], revealed that the regional aerosol is comprised very largely of ammonium nitrate and sulphate and secondary organic aerosol. Findings suggest that international abatement of secondary aerosol precursors may be the most effective measure to fulfil the requirements of the European Directive 1999/30/CE by lowering the regional background.
Keywords: PM10; Vehicle emissions; Long-range transport; Meteorology; Secondary aerosol; Nitrate; Sulphate;
Coupling of the Weather Research and Forecasting Model with AERMOD for pollutant dispersion modeling. A case study for PM10 dispersion over Pune, India by Amit P. Kesarkar; Mohit Dalvi; Akshara Kaginalkar; Ajay Ojha (1976-1988).
The prediction of spatial variation of the concentration of a pollutant governed by various sources and sinks is a complex problem. Gaussian air pollutant dispersion models such as AERMOD of the United States Environmental Protection Agency (USEPA) can be used for this purpose. AERMOD requires steady and horizontally homogeneous hourly surface and upper air meteorological observations. However, observations with such frequency are not easily available for most locations in India. To overcome this limitation, the planetary boundary layer and surface layer parameters required by AERMOD were computed using the Weather Research and Forecasting (WRF) Model (version 2.1.1) developed by the National Center for Atmospheric Research (NCAR). We have developed a preprocessor for offline coupling of WRF with AERMOD. Using this system, the dispersion of respirable particulate matter (RSPM/PM10) over Pune, India has been simulated. Data from the emissions inventory development and field-monitoring campaign (13–17 April 2005) conducted under the Pune Air Quality Management Program of the Ministry of Environment and Forests (MoEF), India and USEPA, have been used to drive and validate AERMOD. Comparison between the simulated and observed temperature and wind fields shows that WRF is capable of generating reliable meteorological inputs for AERMOD. The comparison of observed and simulated concentrations of PM10 shows that the model generally underestimates the concentrations over the city. However, data from this single case study would not be sufficient to conclude on suitability of regionally averaged meteorological parameters for driving Gaussian models like AERMOD and additional simulations with different WRF parameterizations along with an improved pollutant source data will be required for enhancing the reliability of the WRF–AERMOD modeling system.
Keywords: Pollutant dispersion; Regional weather models; Coupling to air quality model; PM10; Urban air quality;
Characterizations of chemical oxidants in Mexico City: A regional chemical dynamical model (WRF-Chem) study by Xuexi Tie; Sasha Madronich; GuoHui Li; Zhuming Ying; Renyi Zhang; Agustin R. Garcia; Julia Lee-Taylor; Yubao Liu (1989-2008).
The formation of chemical oxidants, particularly ozone, in Mexico City were studied using a newly developed regional chemical/dynamical model (WRF-Chem). The magnitude and timing of simulated diurnal cycles of ozone (O3), carbon monoxide (CO) and nitrogen oxides (NO x ), and the maximum and minimum O3 concentrations are generally consistent with surface measurements. Our analysis shows that the strong diurnal cycle in O3 is mainly attributable to photochemical variations, while diurnal cycles of CO and NO x mainly result from variations of emissions and boundary layer height. In a sensitivity study, oxidation reactions of aromatic hydrocarbons (HCs) and alkenes yield highest peak O3 production rates (20 and 18 ppbv h−1, respectively). Alkene oxidations, which are generally faster, dominate in early morning. By late morning, alkene concentrations drop, and oxidations of aromatics dominate, with lesser contributions from alkanes and CO. The sensitivity of O3 concentrations to NO x and HC emissions was assessed. Our results show that daytime O3 production is HC-limited in the Mexico City metropolitan area, so that increases in HC emissions increase O3 chemical production, while increases in NO x emissions decrease O3 concentrations. However, increases in both NO x and HC emissions yield even greater O3 increases than increases in HCs alone. Uncertainties in HC emissions estimates give large uncertainties in calculated daytime O3, while NO x emissions uncertainties are less influential. However, NO x emissions are important in controlling O3 at night.
Keywords: Tie et al.; WRF-Chem; Air quality; Mexico city;
Benzene and toluene influence with or without nitrogen dioxide on inorganic pigments of works of art—Part II by T. Agelakopoulou; I. Bassiotis; E. Metaxa; F. Roubani-Kalantzopoulou (2009-2018).
Air pollution has a great impact on the social and economic aspects all over the world. In order to account the human interaction with the atmospheric environment, a suitable scientific basis is needed.That is why six physicochemical quantities have been determined in a previous work for each one heterogeneous system between organic volatile pollutants and oxide-pigments of works of art. This investigation is extended in order to determine experimentally five new ones. Thus, a more precise contribution to the elucidation of the mechanism of the deterioration of various works of art in museums is achieved. These physicochemical quantities are: (1) local adsorption energies, (2) local monolayer capacities, (3) local adsorption isotherms, (4) density probability function, and (5) pollutant concentration on the oxide-pigment at equilibrium. All these adsorption parameters mentioned above have been calculated as a function of experimental time for the systems: C6H6/TiO2, C6H6/NO2/TiO2, C6H6/Cr2O3, C6H6/NO2/Cr2O3, C6H5CH3/TiO2, C6H5CH3/NO2/TiO2, C6H5CH3/Cr2O3, C6H5CH3/NO2/Cr2O3, C6H6/PbO, C6H6/NO2/PbO, C6H5CH3/PbO, and C6H5CH3/NO2/PbO for the first time. Thus, in this work we shall stress the recent new aspect of Reversed Flow-(Inverse) Gas Chromatography (RF-GC or RF-IGC), i.e. the time-resolved chromatography related to the evaluation of some important adsorption parameters. Gas Chromatography is a promising meeting place of surface science and atmospheric chemistry.
Keywords: Reversed Flow-Gas Chromatography; Inverse Gas Chromatography; Benzene; Toluene; Adsorption; Local parameters;
Efflorescence relative humidity of airborne sodium chloride particles: A theoretical investigation by Yonggang Gao; Shing Bor Chen; Liya E. Yu (2019-2023).
The previously developed theoretical model [Gao, Y., Chen, S.B., Yu, L.E., 2006. Efflorescence relative humidity for ammonium sulfate particles. Journal of Physical Chemistry A, 110, 7602–7608], which has successfully predicted the efflorescence relative humidity (ERH) of ammonium sulfate ((NH4)2SO4) particles at room temperature, is employed to estimate the ERH of sodium chloride (NaCl) particles in sizes ranging from 6 nm to 20 μm. The theoretical predictions well agree with the reported experimental data in literatures. When the NaCl particles are larger than 70 nm, the ERH decreases with decreasing dry particle sizes, and reach a minimum around 44% RH, otherwise the ERH increases with decreasing dry particle sizes (<70 nm) because of the Kelvin effect. Compared with (NH4)2SO4 particles, the Kelvin effect on ERH is stronger for NaCl particles smaller than 30 nm, while the dry particle size exerts weaker influence on NaCl particles larger than 70 nm.
Keywords: Homogeneous nucleation; Efflorescence relative humidity; Kelvin effect; Hygroscopicity;