Atmospheric Environment (v.42, #16)
Editorial board (i).
Chemistry of secondary organic aerosol: Formation and evolution of low-volatility organics in the atmosphere by Jesse H. Kroll; John H. Seinfeld (3593-3624).
Secondary organic aerosol (SOA), particulate matter composed of compounds formed from the atmospheric transformation of organic species, accounts for a substantial fraction of tropospheric aerosol. The formation of low-volatility (semivolatile and possibly nonvolatile) compounds that make up SOA is governed by a complex series of reactions of a large number of organic species, so the experimental characterization and theoretical description of SOA formation presents a substantial challenge. In this review we outline what is known about the chemistry of formation and continuing transformation of low-volatility species in the atmosphere. The primary focus is chemical processes that can change the volatility of organic compounds: (1) oxidation reactions in the gas phase, (2) reactions in the particle phase, and (3) continuing chemistry (in either phase) over several generations. Gas-phase oxidation reactions can reduce volatility by the addition of polar functional groups or increase it by the cleavage of carbon–carbon bonds; key branch points that control volatility are the initial attack of the oxidant, reactions of alkylperoxy (RO2) radicals, and reactions of alkoxy (RO) radicals. Reactions in the particle phase include oxidation reactions as well as accretion reactions, non-oxidative processes leading to the formation of high-molecular-weight species. Organic carbon in the atmosphere is continually subject to reactions in the gas and particle phases throughout its atmospheric lifetime (until lost by physical deposition or oxidized to CO or CO2), implying continual changes in volatility over the timescales of several days. The volatility changes arising from these chemical reactions must be parameterized and included in models in order to gain a quantitative and predictive understanding of SOA formation.
Keywords: Secondary organic aerosol; Semivolatile organic compounds; Biogenic hydrocarbons; Particle-phase reactions;
Aerosol dry deposition on vegetative canopies. Part I: Review of present knowledge by Alexandre Petroff; Alain Mailliat; Muriel Amielh; Fabien Anselmet (3625-3653).
This paper reviews the present knowledge of aerosol dry deposition, with respect to modelling and experimental aspects. In the first part, special attention is given to the existing mechanistic models, either with an analytical or a differential structure. Their predictions are compared against available measurements for grass and forest environments, obtained under controlled aerosol size and aerodynamic conditions. The observed differences are largely related to the parameterisation of the aerosol collection within the canopy. In the second part, existing experimental results are reviewed and a synthesis is provided through different inter-comparisons concerning: (1) the influence of atmospheric stability on fine particle deposition, (2) the evolution of coarse aerosol deposition with aerodynamic conditions and (3) the aerosol size dependence of deposition on grass and forest canopies. A wider compilation of measurements obtained on different canopies is finally proposed.
Keywords: Dry deposition; Aerosol particles; Vegetative canopy; Process-oriented models; Experimental results;
Aerosol dry deposition on vegetative canopies. Part II: A new modelling approach and applications by Alexandre Petroff; Alain Mailliat; Muriel Amielh; Fabien Anselmet (3654-3683).
Keywords: Dry deposition; Aerosol particles; Vegetative canopy; Statistical mechanical model; Experimental validation;
Influence of biomass burning on wintertime fine particulate matter: Source contribution at a valley site in rural British Columbia by Cheol-Heon Jeong; Greg J. Evans; Tom Dann; Mark Graham; Dennis Herod; Ewa Dabek-Zlotorzynska; Dave Mathieu; Luyi Ding; Daniel Wang (3684-3699).
Particulate matter (PM) speciation data were collected between November 2004 and August 2006 in the rural valley area of British Columbia, Canada. Source apportionment of PM was performed using a receptor model, positive matrix factorization (PMF), to identify possible sources of PM and determine the influence of each identified source on local air quality. High concentrations of PM2.5 (<2.5 μm) were observed in winter months with an average of 18 μg m−3, while the average concentration in summer months was approximately 6 μg m−3. PMF apportioned the PM2.5 mass into seven factors identified as Na-rich, secondary sulfate, wood burning, wood processing, crustal material, traffic, and winter heating. The most important sources affecting ambient air quality in the deep valley rural area were wood burning and winter heating factors. In winter the wood burning and winter heating sources accounted for approximately 31% and 43% of the total PM2.5 mass, respectively, indicating the significant influence of biomass burning in the rural area. The wood burning and winter heating factors were highly associated with high organic carbon and volatile organic compounds. The identity of the sources was further elucidated by exploring their relationship with other measured parameters; a correlation study was conducted to evaluate relationships between the sources, gaseous pollutants, and meteorological variables.
Keywords: PM; PM2.5; Source apportionment; PMF; Wood burning;
Simulations of Mideast transboundary ozone transport: A source apportionment case study by E. Weinroth; M. Luria; C. Emery; A. Ben-Nun; R. Bornstein; J. Kaplan; M. Peleg; Y. Mahrer (3700-3716).
The Regional Atmospheric Modeling System (RAMS), Comprehensive Air Quality Model with Extensions (CAMx), and a new emissions inventory were used to study O3 formation downwind from the Israeli coast during summer 1997. While RAMS reproduced the observed diurnal variation of surface wind speeds and temperatures reasonably well, directions were somewhat less correlated. CAMx generally also reproduced the timing, location, and magnitude of measured surface and 300-m O3 max over Jerusalem, but also showed an even larger concurrent max over western Jordan, an area without observations. Observed near-zero nighttime surface O3 values, however, were over predicted because the CAMx grid was too large to accurately account for local emissions and titration effects. CAMx also generally accurately predicted another observed 300 m local max near the Dead Sea, but could not account for a unique O3 depletion mechanism from bromine monoxide released from its water surface. Factor-separation analysis showed that transportation emissions produced 66% and 29% of the Jerusalem and Jordan 300-m simulated maxima, respectively, while power plant emissions produced about 35% and 62%, respectively.
Keywords: Air quality modeling; Mesoscale meteorology; Atmospheric chemistry; Emissions modeling; Model evaluation;
Aerosol thermodynamics of potassium salts, double salts, and water content near the eutectic by James T. Kelly; Anthony S. Wexler; Chak K. Chan; Man N. Chan (3717-3728).
Water uptake by hygroscopic constituents of atmospheric particles has implications for climate and health. This article focuses on three topics related to calculating particle water uptake. First, an electrodynamic balance (EDB) is used to measure water activity for supersaturated binary KNO3 and KCl solutions. The EDB measurements for KNO3 confirm earlier predictions, while those for KCl confirm earlier measurements. Second, our earlier theory for the variation in mutual deliquescence relative humidity (MDRH) with temperature (T) is extended to double salt systems. The MDRH(T) equation for double salt systems reduces to the earlier equation under some conditions, and predictions for two systems are in reasonable agreement with solubility-based calculations. Finally, an approximate treatment of water uptake in the MDRH region (i.e., near the eutectic) is evaluated, and a new approach is developed that accounts for particle composition. The new approach represents predictions of a benchmark model well and eliminates most of the error associated with the earlier method. Although simple treatments of water uptake near the eutectic may introduce error into equilibrium calculations, their use can sometimes be justified based on inherent limitations of aerosol representations in chemistry-transport models. Results of this study can be used to improve calculations of water content in atmospheric aerosol models.
Keywords: Deliquescence; Potassium; Hydrate; Eutonic; Supersaturated;
Characteristics of particle formation events in the coastal region of Korea in 2005 by Young-Gon Lee; Hwa-Woon Lee; Myoung-Soo Kim; Chee Young Choi; Jiyoung Kim (3729-3739).
Measurements of particle number size distribution with diameters ranging from 10 to 487 nm, meteorological parameters and two pollutant gases (ozone (O3) and sulfur dioxide (SO2)) were made to investigate characteristics of new particle formation and growth events at the western coastal region of South Korea in 2005. Among 291 days of Scanning Mobility Particle Sizer (SMPS) measurements, 56 days (about 19.2%) were identified as particle formation events. In particular, 48 days were classified into significant nucleation events. During the cold season, the events are most frequently occurred. Particle growth rates during the cold season were in the range of 1.0–15.7 nm h−1 with the mean of 5.9 nm h−1.Most of the nucleation events were observed at the conditions of high UV-B irradiance (>50 mW m−2) and low relative humidity (<60%). The SO2 concentration on nucleation event days was higher than that of non-event days, whereas the O3 concentration between event and non-event days did not show any significant difference. The nucleation events were also found to be associated with a sea breeze blown from northwest or southwest direction, indicating that the air masses may be originated from the Asian continent and accompanied with cold air outbreak behind cold fronts.
Keywords: Particle formation; Nucleation event; Particle growth; Growth rate; Aerosol;
Long-term trend of chemical composition of wet atmospheric precipitation during 1986–2006 at Shenzhen City, China by Yilong Huang; Yanglin Wang; Liping Zhang (3740-3750).
In order to understand the long-term trend of chemical composition of wet atmospheric precipitation, the precipitation samples were collected for the time period from 1986 to 2006 at Shenzhen City, China. All the rainwater samples were analyzed for pH, conductivity, Cl−, F−, SO4 2−, NO3 −, NH4 +, Na+, K+, Ca2+ and Mg2+ concentration. Average pH during 1986–2006 was 5.02, which is considerably higher compared to those reported in many other cities of the typical acid precipitation regions around the world. A significantly increasing trend (r=0.44 at 2% level) was observed for NO3 − and a decreasing trend for SO4 2− (r=−0.12 at 31% level), NH4 + (r=−0.34 at 7% level) and Ca2+ (r=−0.33 at 7% level), and they together result in the overall decreasing trend (at <0.1% significance level) of pH. The concentrations of SO4 2−, NO3 − and Ca2+ were high compared to some developed countries and areas, but low compared to some other Chinese cities and some developing countries. NH4 + was much lower in precipitation in Shenzhen than it was in some developed countries. We find significant correlations between dust-derived cations and acidic anions, such as Ca2+ and SO4 2−, Ca2+ and Cl−, Mg2+ and SO4 2−, Mg2+ and Cl−, Mg2+ and NO3 −, K+ and Cl−, K+ and F−, indicating that acid pollutants might be absorbed on particulate substances and react with alkaline cations. Evidence is found that anthropogenic and crustal sources have made significant contributions to both acidification and neutralization of precipitation in Shenzhen.
Keywords: Chemical composition; Atmospheric precipitation; Non-sea-salt fraction; Enrichment factor;
Modeling the effects of ship emissions on coastal air quality: A case study of southern California by Satish Vutukuru; Donald Dabdub (3751-3764).
Impact of emissions from ocean-going ships on ozone and particulate matter concentrations is quantified using UCI-CIT model for the South Coast Air Basin of California (SoCAB). The modeling domain encompasses Los Angeles and Long Beach ports and part of the Pacific Ocean that is traversed by ships to visit these ports. Impacts are assessed for a base year (2002) and a future year (2020) by analyzing results from simulations of a three-day summer episode. Contribution of ship emissions to peak 1-h and 8-h ozone concentrations is predicted to be up to 29 and 24 ppb, respectively, for the year 2002. Similarly, particulate nitrate and sulfate concentrations increase up to 12.8 and 1.7 μg m−3, respectively, in the basin when ship emissions are included. Maximum impacts are predicted to occur along the coasts of Ventura and Los Angeles and also at inland locations near Simi Valley. Future year simulations show substantial increase in impacts from ships due to expected growth in ship emissions. Ozone increases are as high as 59 ppb for land-based locations when estimates of ship emissions for 2020 are included. Similarly, particulate nitrate and sulfate increase up to 14 and 2.5 μg m−3. The results of this study show that control of ship emissions is important to mitigate air pollution.
Keywords: Urban air quality; Ship emissions; Ozone; Atmospheric aerosols; Regional modeling;
Modeling weekday to weekend changes in emissions and ozone in the Los Angeles basin for 1997 and 2010 by Greg Yarwood; John Grant; Bonyoung Koo; Alan M. Dunker (3765-3779).
In this study, we used numerical models to investigate weekday to weekend ozone differences in the Los Angeles (LA) basin in 1997 and 2010. We developed relatively complete descriptions of weekday to weekend emission changes for nitrogen oxides (NO x ) with 80% of the weekday NO x emissions receiving a weekend adjustment in 1997 and 67% in 2010. Weekend NO x decreases of 34% on Saturday and 45% on Sunday relative to weekdays for 1997 are predicted to become slightly greater by 2010 and are dominated by NO x decreases for on-road vehicles (especially heavy-duty diesel vehicles) and off-road construction equipment. Weekend anthropogenic reactive organic gas (ROG) decreases for 1997 (12% on Saturday and 16% on Sunday) are smaller than for NO x and become even smaller in 2010. However, there is less certainty in the weekend ROG emission changes because only 47% of the weekday ROG emissions received a weekend adjustment in 1997 and only 21% in 2010. The ozone modeling used multiple representations of the meteorology and chemistry in order to identify results that are consistent across these inputs. Weekend ozone increased in central portions of the basin in response to weekend NO x and ROG decreases for both 1997 and 2010, with both the SAPRC99 and CB4 chemical mechanisms, and with all meteorological data sets. Weekend ozone decreased in other portions of the basin in all models. Comparing 2010 to 1997, weekend ozone increases are smaller and confined to smaller portions of the LA basin near the Pacific coast, whereas weekend ozone decreases are larger and more widespread in 2010. For 2010, all models show lower 8-h ozone on Sunday than weekdays in the Riverside/San Bernardino area. First-order sensitivity analysis (via the decoupled direct method) shows that the weekday/weekend ozone changes are mainly due to the NO x emission changes. Also, the weekday/weekend ozone changes for 2010 are sensitive to the choice of initial and boundary concentrations.
Keywords: Weekend ozone; Los Angeles ozone; Photochemical modeling; CAMx; NO x emissions; ROG emissions; Weekend emissions;
Implications of changing urban and rural emissions on non-methane hydrocarbons in the Pearl River Delta region of China by J.H. Tang; L.Y. Chan; C.Y. Chan; Y.S. Li; C.C. Chang; X.M. Wang; S.C. Zou; Barbara Barletta; D.R. Blake; Dui Wu (3780-3794).
Guangzhou (GZ) is one of the highly industrialized and economically vibrant cities in China, yet it remains relatively understudied in terms of its air quality, which has become severely degraded. In this study, extensive air sampling campaigns had been conducted at GZ urban sites and in Dinghu Mountain (DM), a rural site, in the Pearl River Delta (PRD) during the spring of 2001 and 2005. Additionally, roadside and tunnel samples were collected in GZ in 2000 and 2005. Later, exhaust samples from liquefied petroleum gas (LPG)- and gasoline-fueled taxis were collected in 2006. All samples were analyzed for C2–C10 non-methane hydrocarbons (NMHCs). NMHC profiles showed significant differences in the exhaust samples between gasoline- and LPG-fueled taxis. Propane (47%) was the dominant hydrocarbon in the exhaust of the LPG-fueled taxis, while ethene (35%) was the dominant one in that of gasoline-fueled taxis. The use of LPG-fueled buses and taxis since 2003 and the leakage from these LPG-fueled vehicles were the major factors for the much higher level of propane in GZ urban area in 2005 compared to 2001. The mixing ratios of toluene, ethylbenzene, m/p-xylene and o-xylene decreased at the GZ and DM sites between 2001 and 2005, especially for toluene in GZ, despite the sharp increase in the number of registered motor vehicles in GZ. This phenomenon was driven in part by the closure of polluting industries as well as the upgrading of the road network in urban GZ and in part by the implementation of more stringent emission standards for polluting industries and motor vehicles in the PRD region.
Keywords: NMHCs; LPG; PRD; Industrial emissions; Guangzhou;
Conservation tillage reduces PM10 emissions in dairy forage rotations by N.M. Madden; R.J. Southard; J.P. Mitchell (3795-3808).
The San Joaquin Valley (SJV) is a United States Environmental Protection Agency (USEPA) serious non-attainment area for PM10, particulate matter with an aerodynamic diameter <10 μm. At certain times of the year, PM10 is composed mostly of soil-derived material. The correspondence of air quality violations with intense tillage activities and PM10 composition has focused attention on row crop agriculture as a potential major contributor to PM10. This two-year study compared conservation (CT) and standard tillage (ST) systems in dairy forage production to determine if, and to what extent, CT can reduce agricultural PM10. Vertical profiling methods were used to calculate PM10 emission factors for both systems at two farm locations.Test results showed CT reduced PM10 emissions by about 85% on both farms in spring 2004 and by 52% on one farm to 93% on another farm in spring 2005. PM10 reductions were mainly due to the fewer number of tillage operations in CT systems (zero or one operation compared to three to six in ST) and the higher soil water contents at which CT operations can be performed.Aside from soil moisture, degree of soil pulverization, characterized in the second year of this study by weighted mean ped diameter (WMPD) also proved to be an important determinant of PM10 emissions. The ST second disking always had a higher PM10 emission factor than the first disking despite any change in soil water content. The WMPD decreased 39% between the two diskings.Large discrepancies between PM10 emission factors measured in this study and those used for regulatory purposes in California emphasize the continued need to refine monitoring strategies under varying field conditions to improve accuracy of emission factors and to understand how soil and cropping management affect dust production.
Keywords: PM10; Emission factors; Conservation tillage; Soil water content; Weighted mean ped diameter;
Simultaneous determination of aliphatic and aromatic amines in ambient air and airborne particulate matters by gas chromatography-mass spectrometry by Mehmet Akyüz (3809-3819).
A gas chromatography-mass spectrometry (GC-MS) method has been proposed for the simultaneous determination of aliphatic and aromatic amines in ambient air and airborne particulate matters (PMs). The method includes collection of the particulate matters (PM2.5 and PM10) using dichotomous Partisol 2025 sampler followed by extraction of the compounds into acidic solution, and pre-concentration of the compounds by percolating the air samples through the acidic solution, then ion-pair extraction of amines with bis-2-ethylhexylphosphate and derivatisation with isobutyl chloroformate prior to their GC-MS analysis in both electron impact and positive and negative ion chemical ionisation mode as their isobutyloxycarbonyl (isoBOC) derivatives. In the present study, ambient air and airborne particulate samples collected in Zonguldak province during summer and winter times of 2006–2007 were analysed for aliphatic and aromatic amines by the proposed method and the method was shown to be suitable for the simultaneous determination of these compounds at the levels of pg m−3 in air and airborne particulate samples. The seasonal distributions of bioactive amines in concentrations in ambient air and airborne PMs were evaluated as they are significant for the estimation of their effects on the environment and human health. The concentration levels of water soluble amines fluctuate significantly within a year with higher means and peak concentrations, probably due to the increased emissions from coal-fired domestic and central heating, in the winter times compared to the summer times. The results indicated that the relative amine content in particulates modulates with molecular mass and time of the year and the relative amine content especially in fine fractions of inhalable airborne particulates increases with the molecular mass of species but decreases with temperature.
Keywords: GC-MS; Aliphatic and aromatic amines; Ambient air; Airborne particulates;
Inter-comparison of receptor models for PM source apportionment: Case study in an industrial area by M. Viana; M. Pandolfi; M.C. Minguillón; X. Querol; A. Alastuey; E. Monfort; I. Celades (3820-3832).
Receptor modelling techniques are used to identify and quantify the contributions from emission sources to the levels and major and trace components of ambient particulate matter (PM). A wide variety of receptor models are currently available, and consequently the comparability between models should be evaluated if source apportionment data are to be used as input in health effects studies or mitigation plans. Three of the most widespread receptor models (principal component analysis, PCA; positive matrix factorization, PMF; chemical mass balance, CMB) were applied to a single PM10 data set (n=328 samples, 2002–2005) obtained from an industrial area in NE Spain, dedicated to ceramic production. Sensitivity and temporal trend analyses (using the Mann–Kendall test) were applied. Results evidenced the good overall performance of the three models (r 2>0.83 and α>0.91×between modelled and measured PM10 mass), with a good agreement regarding source identification and high correlations between input (CMB) and output (PCA, PMF) source profiles. Larger differences were obtained regarding the quantification of source contributions (up to a factor of 4 in some cases). The combined application of different types of receptor models would solve the limitations of each of the models, by constructing a more robust solution based on their strengths. The authors suggest the combined use of factor analysis techniques (PCA, PMF) to identify and interpret emission sources, and to obtain a first quantification of their contributions to the PM mass, and the subsequent application of CMB. Further research is needed to ensure that source apportionment methods are robust enough for application to PM health effects assessments.
Keywords: PMF; PCA-MLRA; CMB; Emission profile; Sensitivity analysis; Temporal trend analysis; Ceramic industry;
Using measurements in urban areas to estimate turbulent velocities for modeling dispersion by Akula Venkatram; Marko Princevac (3833-3841).
Keywords: Friction velocity; Monin–Obukhov similarity; Standard deviation of turbulent velocities; Stable boundary layer; Unstable boundary layer; Wilmington; VTMX;
Examining the sensitivity of MM5–CMAQ predictions to explicit microphysics schemes and horizontal grid resolutions, Part I—Database, evaluation protocol, and precipitation predictions by Ashley Queen; Yang Zhang; Robert Gilliam; Jonathan Pleim (3842-3855).
Wet deposition of chemical species is one of the most difficult processes to simulate in three-dimensional (3-D) air quality models, due to the complex interplay among meteorology, cloud, and atmospheric chemistry. Different cloud microphysical treatments and horizontal grid resolutions in 3-D models can directly affect simulated clouds, precipitation, and wet deposition. In this study, the performance and sensitivity of the simulated precipitation, concentrations, and wet deposition to different explicit microphysics schemes and horizontal grid resolutions are evaluated for August and December 2002 for a domain centered over North Carolina (NC). Four explicit microphysics schemes in MM5 are examined: Reisner 1 (R1), Reisner 2 (R2), Dudhia (SI), and Hsie (WR).The precipitation evaluation indicates that monthly-average precipitation amounts are underpredicted by all schemes in both August and December at all sites except for the R1 August simulation that shows overpredictions at National Acid Deposition Program (NADP) sites. An increased sensitivity to microphysics schemes is found at locations in both the coastal plain and mountain regions in August and the mountain region in December. The differences in simulation results in August and December are mainly attributed to seasonal differences in dominant meteorological forcing (mesoscale vs. synoptic, respectively). Among the schemes tested, R2 and SI give the best overall performance in predicting precipitation for both months. These findings are applicable for NC and neighboring states with similar meteorological and emission characteristics.
Keywords: MM5; CMAQ; Explicit microphysics scheme; Wet deposition; Precipitation;
Examining the sensitivity of MM5–CMAQ predictions to explicit microphysics schemes and horizontal grid resolutions, Part II—PM concentrations and wet deposition predictions by Ashley Queen; Yang Zhang (3856-3868).
This part II paper first evaluates the simulated concentrations and wet deposition amounts of NH4 +, NO3 −, and SO4 2− using observations from several networks, then examines their sensitivities to four explicit microphysics schemes: Reisner 1 (R1), Reisner 2 (R2), Dudhia simple ice (SI), and Hsie warm rain (WR). For baseline simulation with R1, the concentrations of NH4 +, NO3 −, and SO4 2− are underpredicted in August. Concentrations of SO4 2− are underpredicted and those of NH4 + and NO3 − are overpredicted in December. The wet deposition amounts of NH4 + and SO4 2− are overpredicted but those of NO3 − are underpredicted in August. The wet deposition amounts of NO3 − and NH4 + are overpredicted but those of SO4 2− are underpredicted in December. The simulated wet deposition amounts are sensitive to various schemes, which are most evident in December, with the best results for NH4 + and NO3 − by WR and the best for SO4 2− by SI. A correlation exists between wet deposition amounts and precipitation in both months, with stronger magnitudes in August. Conversely, in December, as the correlation with precipitation decreases, that with aqueous-phase concentrations increases. These results are consistent with meteorological conditions since the summer convective precipitation events having larger intensities and therefore the meteorological forcing is expected to dominate August correlations. As these intensities decrease in December, the chemical forcing becomes more influential.
Keywords: Model evaluation; MM5; CMAQ; Explicit microphysics scheme; Wet deposition;
Examining the sensitivity of MM5–CMAQ predictions to explicit microphysics schemes and horizontal grid resolutions, Part III—The impact of horizontal grid resolution by Ashley Queen; Yang Zhang (3869-3881).
Examination of model sensitivity to horizontal grid resolutions can help identify optimal compromise in accuracy and computational efficiency for regulatory and research-grade applications of 3-D atmospheric models. In this Part III paper, the performance and sensitivity of simulated precipitation and wet deposition amounts by the MM5/CMAQ model to three horizontal grid resolutions (4-, 12-, and 36-km) are evaluated over North Carolina (NC).In contrast with simulated O3, PM2.5, and some PM2.5 species such as NH4 +, simulated precipitation and wet deposition amounts are quite sensitive to grid resolutions. Compared with results at coarser resolutions, simulated precipitation amounts are lower in both August and December at 4-km, with the largest sensitivities to grid resolutions occurring in mountain and coastal regions of NC. For wet deposition predictions, the model performs the best for NO3 − at 4-km and for NH4 + and SO4 2− at 12-km in August, but the best for NH4 + and NO3 − at 36-km and for SO4 2− at 4-km in December. Such sensitivities and lack of clear trends in model performance at various resolutions can be attributed to seasonalities in meteorology and differences in characteristics of land use, emissions and concentrations of PM precursors, as well as nonlinear responses of chemistry and meteorology to grid resolutions. The overall performance trends demonstrate a high sensitivity in precipitation and wet deposition predictions over complex terrain and the fact that higher grid resolution does not always lead to improved model performance.
Keywords: MM5; CMAQ; Sensitivity; Horizontal grid resolutions; Precipitation; Wet deposition;
Effects of rare-earth fertilizers on the emission of nitrous oxide from agricultural soils in China by Zhangwei Wang; Xiaoshan Zhang; Yujing Mu (3882-3887).
Rare-earth fertilizers have long been used in agriculture in China. The consequences of these applications are of more recent concern. In our study, an experiment was carried out to identify the effects of applying rare-earth fertilizers on emission of nitrous oxide from paddy and dryland soils in northern China. Normal dosage of rare-earth fertilizers only, normal dosage of urea only, normal dosage of urea plus rare-earth fertilizers, and a normal urea application plus a 10-fold increase in the dosage of rare-earth fertilizers were applied to the soils in pots, prepared for our experiment. A static closed-chamber technique was used to measure nitrous oxide emission flux from the soil in the pots before and after fertilization during the experiment. The results show that the application of only rare-earth fertilizers did not have any visible effect on the emission of nitrous oxide from both paddy and dryland soils. Applying a normal dosage rare-earth fertilizers plus urea led to greater emission of nitrous oxide from the soils than only applying the normal dosage of urea. When a 10-fold increase of rare-earth fertilizers dosage was added to a normal dosage of urea, the emission of nitrous oxide from the soils increased even further. We speculate that the application of rare-earth fertilizers leads to an increase of available NH4 +-N from urea hydrolysis and activate bacteria and enzymes in nitrification and de-nitrification.
Keywords: Rare-earth fertilizer; Nitrous oxide emission; Agricultural soils;
On the applicability of XPS for quantitative total organic and elemental carbon analysis of airborne particulate matter by Richard J.J. Gilham; Steve J. Spencer; David Butterfield; Martin P. Seah; Paul G. Quincey (3888-3891).
X-ray photoelectron spectroscopy (XPS) is a widely used surface analysis technique that in recent years has been used by a number of groups to analyse particulate matter collected onto filters. In this communication, XPS is compared to the standard method for determining the ratio of the elemental carbon to total carbon in all forms in the particulates using a PM10 quartz filter sample. The results obtained from the two methods are significantly different, suggesting that XPS gives a better indication of the chemistry of the surface of the particle, whereas the standard method is more relevant to the composition of the particles as a whole. Therefore, each technique has valid applications—XPS may be better for use in those toxicology studies where surface chemistry is important, whereas the standard method may be best for tracing the origin of particles through knowledge of the average particle composition.
Keywords: X-ray photoelectron spectroscopy; Carbon analysis; Elemental carbon; Organic carbon; Particulate matter;
Evaluation of traffic noise pollution and attitudes of exposed individuals in working place by Vinita Pathak; B.D. Tripathi; Virendra kumar Mishra (3892-3898).
The main objective of this paper is to evaluate the noise pollution problem in the Varanasi city and its effect on the exposed people. The study revealed the fact that noise levels have reached an alarming level. The result of the study indicated the fact that 85% of the people were disturbed by traffic noise, about 90% of the people reported that traffic noise is the main cause of headache, high BP problem, dizziness and fatigue. People having higher education and income level are much aware of the health impact due to traffic noise. Marital status was found to be significantly affecting the annoyance level caused by traffic noise. Traffic noise was found to be interfering daily activities such as at resting, reading, communication etc.
Keywords: Noise; Pollution; Traffic; Noise pollution level;
Particulate matter emission by a vehicle running on unpaved road by David Scott Williams; Manoj K. Shukla; Jim Ross (3899-3905).
The particulate matter (PM) emission from unpaved roads starts with the pulverization of surface material by the force of the vehicle, uplifting and subsequent exposure of road to strong air currents behind the wheels. The objectives of the project were to: demonstrate the utility of a simple technique for collecting suspended airborne PM emitted by vehicle running on an unpaved road, determine the mass balance of airborne PM at different heights, and determine the particle size and elemental composition of PM. We collected dust samples on sticky tapes using a rotorod sampler mounted on a tower across an unpaved road located at the Leyendecker Plant Sciences Research Center, Las Cruces, NM, USA. Dust samples were collected at 1.5, 4.5 and 6 m height above the ground surface on the east and west side of the road. One rotorod sampler was also installed at the centre of the road at 6 m height. Dust samples from unpaved road were mostly (70%) silt and clay-sized particles and were collected at all heights. The height and width of the PM plume and the amount of clay-sized particles captured on both sides of the road increased with speed and particle captured ranged from 0.05 to 159 μm. Dust particles between PM10 and PM2.5 did not correlate with vehicle speed but particles ⩽PM2.5 did. Emission factors estimated for the total suspended PM were 10147 g km−1 at 48 km h−1 and 11062 g km−1 at 64 km h−1 speed, respectively. The predominant elements detected in PM were carbon, aluminum and silica at all heights. Overall, sticky tape method coupled with electron microscopy was a useful technique for a rapid particle size and elemental characterization of airborne PM.
Keywords: Particulate matter; Unpaved road; Rotorod; Sticky tape; Emission; Moisture content; Silt and clay;
New Directions: The future modelling requirements to inform policy and legislation of urban air abatement by Akula Venkatram (3906-3907).