Atmospheric Environment (v.40, #24)
Editorial board (i).
Fast evolution of tropospheric Pb- and Zn-rich particles in the vicinity of a lead smelter by M. Choël; K. Deboudt; P. Flament; G. Lecornet; E. Perdrix; S. Sobanska (4439-4449).
Dusts collected on air filters at a Pb–Zn refinery located in northern France were sampled in 1997, 1999 and 2002. The low temporal variability in major elements (Pb, Zn and S) abundances suggested chemical composition of particulate emissions was stable over time. In July 2001 and March 2002, atmospheric aerosols were sampled in the vicinity of the Pb–Zn refinery upwind and downwind from the smelters. Bulk concentrations of major elements (Al, Fe, Pb and Zn) and hydrosoluble ions (Na+, NH4 +, Mg2+, K+, Ca2+, Cl– NO3 – and SO4 2–) were, respectively, determined by atomic absorption spectrometry and ion chromatography. Elemental and molecular individual particle analyses were, respectively, performed by automated SEM–EDX and Raman microspectrometry. Continental air masses (campaign 2001) were characterized by low Na+ and high SO4 2–, NO3 – and NH4 + contents upwind from the smelters. Individual particle analysis of Pb- and Zn-rich airborne particles collected downwind from the refinery indicated elemental associations and molecular speciation were similar to those obtained at the emission: Pb compounds were mainly identified as oxides, sulfates and oxy-sulfates whereas Zn compounds were identified as sulfides. Marine air masses (campaign 2002) were characterized by high Na+ contents upwind from the smelters. Individual particle analysis of Pb- and Zn-rich particles collected downwind from the refinery pointed out a systematic association with Na, not emitted by the refinery, suggesting internal mixing of marine aerosols with heavy-metals dusts emitted by the refinery. Such fast evolution of airborne particles chemical composition in the vicinity of the refinery was further proven by SEM–EDX and Raman microspectrometry mappings showing physical evolution by aggregation or coagulation of Zn- and Pb-rich particles with aged sea-salts.
Keywords: Atmospheric aerosols; Heavy metals; Individual particle analysis; SEM–EDX; Raman;
Water uptake by aerosol: Water activity in supersaturated potassium solutions and deliquescence as a function of temperature by James T. Kelly; Anthony S. Wexler (4450-4468).
Atmospheric aerosol models often calculate water uptake by particles based on information on salt deliquescence and electrolyte mixing rules. Therefore improvements in deliquescence predictions and in the water-activity relations used in mixing rules can improve estimates of size distributions. The primary goals of this work are to derive equations for the variation in the mutual deliquescence relative humidity (MDRH) with temperature (T) for a particle containing an arbitrary number of hydrated and anhydrous salts and to extend the range of validity of water–activity relations reported for binary solutions of KNO3, KCl, KBr, and K2SO4 to greater supersaturations. Equations for MDRH(T) are derived based on the equilibrium conditions that define deliquescence and the Gibbs-Duhem relation. MDRH is calculated from solubility data and the ZSR mixing rule to generate reference values for the equations and to evaluate their reliability. The ZSR mixing rule is also used to predict concentrations of KNO3, KCl, KBr, and K2SO4 in highly supersaturated binary solutions. Polynomial fits are presented that relate water activity to concentration for these solutions. The deliquescence equations derived here predict MDRH(T) for hydrate systems with sufficient accuracy for temperature excursions of about 25 K. MDRH(T) usually follows the trend of DRH(T) for the most soluble salt in the system, while the temperature dependence of saturation concentration can be neglected for some salt systems. A linear temperature dependence for saturation concentration appears necessary to capture MDRH(T) for systems containing Ca(NO3)2·4H2O and CaCl2·6H2O. Consideration of deliquescence for a representative sea-salt system indicates that minor hydrated components have an important influence on the uptake of water by sea-salt particles and should be considered in equilibrium aerosol models. Results of this study improve estimates of water uptake by atmospheric particles containing hydrates and potassium salts.
Keywords: Deliquescence; Mixing rule; Hydrate; Water activity; Supersaturated;
Study of aerosol optical thickness in Hong Kong, validation, results, and dependence on meteorological parameters by A.Y.S. Cheng; M.H. Chan; X. Yang (4469-4477).
Three years of aerosol optical thickness (AOT) measured from 2002 to 2004 in Hong Kong using a ground-based sky radiometer is reported. Comparison of the ground-based optical thickness measurement with the MODIS satellite AOT using a linear regression analysis confirmed the integrity of the ground-based data quality. The MODIS optical thickness obtained from AQUA and TERRA correlates with the sky radiometer data with linear correlation coefficient, R 2, values of 0.804 and 0.625, respectively. Annual mean ground-based AOT at visible channels have increased by 33% and 22% for observations at 400 and 500 nm, respectively. Monthly mean turbidity coefficient varies from 0.20 to 0.56 over the period, while the monthly mean of the Angstrom exponent ranges from 0.12 to 1.34. The variation is due to seasonal nature of the aerosols. Fitting the annual mean AOT values to the Angstrom's equation has revealed a significant 53% increase in the Angstrom exponent (from 0.7 to 1.07) over the three-year period, while the turbidity remains comparable.
Keywords: Aerosol optical thickness; MODIS; Angstrom turbidity; Angstrom exponent;
The emission characteristics and the related malodor intensities of gaseous reduced sulfur compounds (RSC) in a large industrial complex by Ki-Hyun Kim; Eui-Chan Jeon; Ye-Jin Choi; Youn-Seo Koo (4478-4490).
In this study, the concentrations of major reduced sulfur compounds (RSC: H2S, CH3SH, DMS, CS2 and DMDS) were determined from various emission sources located within the Ban-Wall (BW)/ Si-Hwa (SH) industrial complex in Ansan city, Korea. The measurement data were obtained from a total of 202 individual points at 77 individual companies during 2004–2005. The highest RSC concentration levels came most dominantly from H2S (300 (mean) and 0.86 ppb (median)) followed by CS2, while the results of CH3, DMS, and DMDS are notably lower at the mean concentration levels of a few ppb. These data were evaluated further after being grouped into two different classification schemes: 9 industry sectors and 9 processing unit types. The strongest emissions of RSC, when evaluated among different industry sectors, are generally found from such industry types as leather, food, paper/pulp, as well as waste/sewage related ones. In contrast, when these RSC data are compared across different processing units, the highest values were seen most frequently from such units as junction boxes, aeration tanks, and settling tanks. The assessment of data in terms of relative contribution to malodor intensity showed that H2S and CH3SH are more important than others. The overall results of the present study suggest that information combining RSC speciation and types of anthropogenic activities may be used to distinguish the patterns of odorous pollution in areas affected by strong source processes.
Keywords: Reduced sulfur compounds (RSC); H2S; Malodor; Industrial complex; Korea;
New definition and new calculation method of effective average cloud amount by Zuoyong Li; Lihong Peng; Jiayang Wang; Jianqiu Xiong (4491-4500).
Different types of cloud amounts have different influences on the calculation of the radiation energy of the soil–air system. Based on the occurrence of the overlaying of high, medium and low types of clouds and the interaction and interrelationship of information provided by them, this paper puts forwards new concepts of “effective” frequency of occurrences of cloud and “effective” time-average cloud amount and their calculation formulas, while the commonly used calculation formula for time-average cloud amount is treated as a special case of the calculation formula for “effective” time-average cloud amount. Through a principal component analysis of the correlation coefficient matrix formed by conditional probabilities exhibited by any other type of cloud when a certain type of cloud occurs, the normalized weight of the conditional probability exhibited by any other type of cloud when this particular type of cloud occurs is ascertained. When this particular type of cloud is obscured by another type of cloud, the weight can be seen as the probability of this particular type of cloud being obscured by another type of cloud. With the formula for the “effective” frequency of occurrences of cloud and the formula for “effective” average cloud, this probability can be used to calculate the “effective” time-average cloud amount of this particular type of cloud. By applying this method to the analysis and calculation of the “effective” average cloud amount in the four different seasons as observed by 15 observation stations worldwide, this paper finds that the sum of the “effective” time-average cloud amounts of each type of clouds is far closer to the observed value of the total cloud amount than the sum of the time-average cloud amounts derived by using only the calculation formula for time-average cloud amount, with more than 87% of the relative errors of the total cloud amount corrections made by the former being smaller than 15% and all relative errors of the total average cloud corrections made by the latter exceeding 15%.
Keywords: Effective frequency; Effective cloud amount; Conditional probability; Principal component method;
Inter-annual variation in atmospheric Δ14C over the Northern Indian Ocean by Koushik Dutta; Ravi Bhushan; B.L.K. Somayajulu; Neeraj Rastogi (4501-4512).
Radiocarbon (14C) in atmospheric CO2 over the Northern Indian Ocean was measured between 1993 and 2001, by collecting remote maritime air from ship cruises. The Δ14C of atmospheric CO2 over this region decreased from 120±3‰ in 1993 to 85±2‰ in 2001, consistent with the global exponential decreasing trend. The Δ14C values measured in spring of 2001 over the Bay of Bengal and the Arabian Sea were 86±2‰ and 85±3‰, respectively, thus indistinguishable within error limits. Significant inter-annual variations in Δ14C were observed over this region. Input of 14C-free fossil fuel CO2 from the South Asian continent significantly influence springtime Δ14C values over the Northern Indian Ocean, through transport by meridional atmospheric circulation. Additional variations are possibly caused by enhanced inputs of 14C-rich biogenic CO2, during El Niño/Southern Oscillation events.
Keywords: Radiocarbon; Atmosphere; Fossil fuel CO2; Indian Ocean; ENSO;
Characterizations of aerosols over the Beijing region: A case study of aircraft measurements by Qiang Zhang; Chunsheng Zhao; Xuexi Tie; Qiang Wei; Mengyu Huang; Guohui Li; Zhuming Ying; Chengcai Li (4513-4527).
Using optical spectrometer probes mounted on a light aircraft, fine-mode and coarse-mode aerosol size distributions were recorded within and above the planetary boundary layer in the vicinity of Beijing on 29 April 2005. A regional transport and dynamical model (Weather Research and Forecast coupled with a tracer transport model—WRF-Tracer) and satellite (moderate-resolution imaging spectroradiometer—MODIS) data were applied to analyze and interpret the aircraft measurements. The results show that the aerosol pollution in the Beijing region was very heavy on 29 April 2005. The satellite measured aerosol optical depth (AOD) over this region was exceeded to 2.0. The aerosol mass concentrations reached up to 160 μg m−3 in some cases. The analysis suggests that three important source regions influenced this heavy aerosol pollution in the Beijing region, including: (1) the long-range transport from the Gobi Desert with diameters ranging from 0.5 to 4 μm, (2) the transport from the south of Beijing area, and (3) the local emissions over Beijing. A strong vertical gradient of aerosol concentrations in Beijing at Shahe Airport was observed. The fine aerosol particles are dominated below the planetary boundary layer (PBL) with number concentrations of 5000 cm−3, diameters of 0.3 μm, and mass concentrations of 144 μg cm−3. However, the coarse aerosol particles (dust) are dominated above the PBL with number concentrations of 2.5 cm−3, diameters of 2.5 μm, and mass concentrations of 120 μg m−3. There is an inversion layer at the top of the PBL, and this inversion layer acts to suppress mixing between the PBL and overriding troposphere and stabilizes desert dust layer that is being transported overhead. This study demonstrates that the measurement from the aircraft together with the WRF-tracer and MODIS data provides good information to understand the origins and spatial distribution of aerosol particles in Beijing. Note that this analysis is based on the measurement on 29 April 2005. Thus it is considered as an example or a case study.
Keywords: Aerosol; Aircraft; Beijing; WRF-tracer; MODIS;
Multiple oxygen and sulfur isotope compositions of atmospheric sulfate in Baton Rouge, LA, USA by Kathryn A. Jenkins; Huiming Bao (4528-4537).
Secondary atmospheric sulfates (SAS) is the ultimate oxidation product and sink for sulfur gases of biological, volcanic, and anthropogenic origins on Earth. Their presence in the atmosphere as aqueous or solid phases contributes to acid rain and climate change, thus, understanding SAS formation pathways is pertinent. There has been extensive measurement of δ 34S values for SAS, which mainly aimed at source identification. Relatively fewer oxygen isotope compositions (δ 18O, Δ17O), which are most useful for resolving competing oxidation pathways, were available, however. This study represents the first effort to characterize the Δ17O, δ 18O, and δ 34S simultaneously for SAS in a tropospheric air shed. We measured a total of 20 samples collected in Baton Rouge (LA, USA) during a 600-day period. The isotope compositions for atmospheric sulfate range from +0.25‰ to +1.43‰ for Δ17O, +11.8‰ to +19.3‰ for δ 18O, and −1.4‰ to +3.8‰ for δ 34S. No apparent correlation is found among Δ17O, δ 18O, or δ 34S values. The Δ17O has no seasonal variation and its values are consistent with an oxidation pathway dominated by aqueous H2O2. The δ 18O and δ 34S are within the range of those observed in other sites around the world and are not characteristic for Baton Rouge. Despite the huge variability in atmospheric condition among mid-latitude sites, the long-term average Δ17O value for SAS appears to fall within a fairly narrow range from +0.6‰ to +0.8‰, which is ∼1‰ to 2‰ lower than those in polar sites.
Keywords: Atmospheric sulfate; Rainwater; Isotope compositions; Oxygen; Sulfur; Louisiana;
Determination of Henry's law constants of organochlorine pesticides in deionized and saline water as a function of temperature by Banu Cetin; Serdar Ozer; Aysun Sofuoglu; Mustafa Odabasi (4538-4546).
The Henry's law constant (H) is an important parameter that is required to estimate the air–water exchange of semi-volatile organic compounds. Henry's law constants for 17 banned/restricted/currently used organochlorine pesticides (OCPs) were experimentally determined using a gas-stripping technique in deionized and saline water (3%) over a temperature range of 5–35 °C. H values (at 25 °C) ranged between 0.066±0.037 Pa m3 mol−1 (endosulfan II) and 62.0±24.2 Pa m3 mol−1 (heptachlor) in deionized water while the range in saline water was 0.28±0.03 Pa m3 mol−1 (γ-HCH) and 135.2±31.3 Pa m3 mol−1 (heptachlor). The increase in dimensionless Henry's law constants (H′) for OCPs over the studied temperature range was between 3 (γ-HCH)-19 times (chlorpyrifos) and 3 (endosulfan II)-80 times (trans-nonachlor) in deionized and saline water, respectively. The calculated enthalpies of phase change (ΔH H) were within the ranges previously reported for OCPs and other organic compounds (23.8–100.2 kJ mol−1). The salting-out constant, k s, ranged between 0.04 (γ-HCH) and 1.80 L mol−1 (endosulfan II) indicating the importance of assessing the H values of OCPs in saline water to accurately determine their partitioning and fate in seawater.
Keywords: Organochlorine pesticides; Henry's law constant; Gas-stripping technique; Salting-out effect;
Emission control options for power two wheelers in Europe by Leonidas Ntziachristos; Athanasios Mamakos; Zissis Samaras; Anastasios Xanthopoulos; Eleftherios Iakovou (4547-4561).
This paper quantifies the emission contribution of motorcycles and mopeds in Europe, in the period 1999–2012. Projections show that these vehicles will emit more than 7% and 20% of total road transport CO and HC, respectively, by the year 2012, if no additional regulatory measures are taken. In contrast, they will continue to be negligible NO x (0.7%) and CO2 (<1%) emitters, while their particulate matter (PM) emission contribution is expected to decline to below 1% in the future. The relative importance of their emissions, however, increases in urban environments, especially in southern European countries, which host large fleets of small two wheelers. Hence, further regulatory measures are being considered which include durability requirements for the emission controls, in-use compliance and roadworthiness procedures, on-board diagnostics, control of evaporation emissions, PM specific measures and new steps for emission standards. The study quantifies the environmental benefits and the costs associated with each measure, and calculates cost-effectiveness figures which may be used to evaluate each policy option. Results show that for the reduction of HC emissions, both evaporation control and roadworthiness tests are cost-effective while a further tightening of the emission standards for mopeds will bring the largest benefit. Additionally, on-board diagnosis for motorcycles is found to be an expensive measure with questionable effectiveness, while the replacement of mineral with synthetic lubricants would bring clear benefits with respect to PM of 2-stroke engines.
Keywords: Motorcycle; Moped; Emission standard; Cost-effectiveness; Emission projection;
An examination of the CMAQ simulations of the wet deposition of ammonium from a Bayesian perspective by Jerry M. Davis; Jenise L. Swall (4562-4573).
The ability of the US Environmental Protection Agency's Community Multi-scale Air Quality (CMAQ) model to simulate the wet deposition of ammonium during 8-week winter and summer periods in 2001 is evaluated using observations from the National Acid Deposition Program (NADP) monitoring sites. The objective of this study is to ascertain the effects of precipitation simulations and emissions on CMAQ simulations of deposition. In both seasons, CMAQ tends to underpredict the deposition amounts. Based on the co-located measurements of ammonium wet deposition and precipitation at the NADP sites and on estimated precipitation amounts for each grid cell, Bayesian statistical methods are used to estimate ammonium wet deposition over all grid cells in the study region. To assess the effect of precipitation on the CMAQ simulations, our statistical method is run twice for each time period, using the simulated precipitation information provided to CMAQ and precipitation estimates based on data collected by the cooperative observer network. During the winter period when stratiform-type precipitation dominates, precipitation amounts do not seem to be a major factor in CMAQ's ability to simulate the wet deposition of ammonium. However, during the summer period when precipitation is mainly generated by convective processes, small portions of the region are identified in which problems with precipitation simulations may be adversely affecting CMAQ's estimates.
Keywords: Ammonium wet deposition; Model evaluation; Bayesian statistical methods; Spatial correlation; Community multi-scale air quality (CMAQ) model; National acid deposition program (NADP); Ammonia emissions;
An asynchronous time-stepping (ATS) integrator for atmospheric applications: Aerosol dynamics by K. Max Zhang; Anthony S. Wexler (4574-4588).
Mixed time integration methods, also known as multiple time-step methods (MTS), have been proposed and implemented successfully to reduce the stiffness of problems in molecular dynamics and solid mechanics, where different time scales are used to integrate different motions or meshes. We apply the similar concept and develop an asynchronous time-stepping (ATS) integrator for atmospheric application. This paper first presents ATS as a generalized ordinary differential equation solver and describes its key components including: (1) global and local time management; (2) dynamic time-scale ordering; and (3) integration and iteration methods. Then we apply ATS to solve stiff problems in aerosol dynamics, where we further introduce several techniques such as grouping particulate species by particle sections to speed up computations. The comparisons between ATS and standard ODE solvers including LSODE, LSODES and VODE in aerosol dynamics simulation are presented, which show that ATS is robust and able to achieve a significant digit average (SDA) value of 2.0 to 3.0 while its speed is around 10 to 100 times faster than LSODE with equivalent accuracy. ATS has been implemented in CMAQ-UCD, a sectional, dynamic aerosol model built on USEPA's CMAQ platform.
Keywords: Stiff problem; Ordinary differential equations (ODE); MTS; Aerosol dynamics; CMAQ-UCD;
Cost effective passive sampling device for volatile organic compounds monitoring by Chongdee Thammakhet; Vilailuk Muneesawang; Panote Thavarungkul; Proespichaya Kanatharana (4589-4596).
A laboratory-built passive sampler was developed as a simple and cost effective device for monitoring volatile organic compounds (VOCs) such as benzene, toluene and xylene (BTX). Common glass bottles (screw cap, 10 ml, 67.6×10.6 mm ID), packed with 75 mg of activated Tenax TA, were used as passive samplers. After exposed to real sample, the adsorbent was desorbed using a laboratory-built thermal desorption device. The analytes were purged to fill a sampling loop and then injected by a gas sampling valve to a gas chromatograph with a flame ionization detector (FID). All parameters, i.e., desorption time, purge flow rate, gas chromatograph conditions were optimized to obtain high sensitivity, resolution and short analysis time. The system was calibrated by BTX standard gas and the linear regression coefficient of greater than 0.99 was obtained with detection limits 0.3, 0.2 and 0.7 μg m−3 for benzene, toluene and xylene, respectively. The proposed method was implemented for the monitoring of BTX at 10 gasoline stations in Hat Yai, Thailand. The concentrations were found in the range of N.D.–19, 12–200 and 23–200 μg m−3 for benzene, toluene and xylene, respectively.
Keywords: Laboratory-built; Passive sampling; VOCs; BTX;
The characterisation of secondary organic aerosol formed during the photodecomposition of 1,3-butadiene in air containing nitric oxide by D.E. Angove; C.J.R. Fookes; R.G. Hynes; C.K. Walters; M. Azzi (4597-4607).
The formation of secondary organic aerosol (SOA) at yields of 0.4–0.5% and having a geometric mean diameter <100 nm has been observed during indoor environmental chamber experiments on 1.0–2.2 ppmv 1,3-butadiene in the presence of 0.5–1.1 ppmv NO. The SOA was collected on glass fibre filters, some of which were acetylated using a pyridine/acetic anhydride mixture immediately after collection. Analysis of the SOA by Fourier transform infrared spectroscopy (FTIR) resulted in bands assigned to OH stretching in alcoholic and carboxylic hydroxyl groups, NO stretching in NO3 and C＝O stretching at 1728 cm−1, the latter indicative of formate esters rather than aldehydes or ketones. Initial NMR spectra showed a broad polymeric-like feature, which separated into peaks representative of monomeric units as the SOA hydrolysed over 3 days. Subsequent GC-MS and NMR analyses were used to identify 18 species, which represented 75–80% of the SOA mass. Some of the unidentified mass is probably composed of organic nitrates. Low vapour pressure (⩽10−7 Torr) species detected were glycerol, threitol, erythritol and isomeric forms tentatively identified as threonic and erythronic acid nitrate. Gel permeation chromatography of acetylated SOA gave a polymer molecular weight distribution range up to ∼4.0×105 g mol−1, with a peak molecular weight of 6.12×104 g mol−1. A chemical mechanism for the formation of endogenous seed aerosol directly from 1,3-butadiene is presented. It is proposed that the SOA is polymeric and composed of C1–C4 oxygenated species, including formate esters and hemiacetal formates.
Keywords: 1,3-butadiene; Secondary organic aerosol; Environmental chamber; Threitol; Erythritol; Hemiacetal;
The sectoral trends of multigas emissions inventory of India by Amit Garg; P.R. Shukla; Manmohan Kapshe (4608-4620).
This paper provides the trends of greenhouse gas (GHG) and local air pollutant emissions of India for 1985–2005. The GHGs covered are six Kyoto gases, namely carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), perfluorocarbons (PFCs), hydrofluorocarbons (HFCs) and sulfur hexafluoride (SF6). The local air pollutants are sulfur dioxide (SO2), nitrogen oxides (NO X ), carbon monoxide (CO) and total suspended particulates (TSP). These estimates incorporate some of the most recent scientific assessments for India.The multigas emissions have varied sectoral and fuel-based dominance, as well as regional distribution patterns. Coal consumption in power sector dominates CO2 and SO2 emissions, while power and road transport equally contribute to NO X emissions. Rice cultivation and livestock-related emissions from the agriculture sector dominate CH4 emissions, while synthetic fertilizer use in the same sector is the major source of N2O emissions. PFC emissions are dominated by C2F6 and CF4 emissions from aluminum production. The majority of HFC emissions are contributed by HFC-23, a by-product during the production of HCFC-22 that is widely used in refrigeration industry. CO emissions have dominance from biomass burning. Particulate emissions are dominated by biomass burning (residential sector), road transport and coal combustion in large plants. These varied emission patterns provide interesting policy links and disjoints, such as—which and where mitigation flexibility for the Kyoto gases, exploring co-benefits of CO2 and SO2 mitigation, and technology and development pathway dependence of emissions. The present inventory assessment is a pointer to the future emission pathways for India wherein local air pollutant and GHG emissions, although connected, may not move in synchronization and therefore would require alignment through well crafted development and environment strategies.
Keywords: Multigas; Kyoto gases; Emission trends;
Mapping the spatial distribution of global anthropogenic mercury atmospheric emission inventories by Simon J. Wilson; Frits Steenhuisen; Jozef M. Pacyna; Elisabeth G. Pacyna (4621-4632).
Keywords: Mercury; Emissions; Global; Anthropogenic; GIS; Mapping; Inventory;
Distributions of O3, CO and hydrocarbons over the Bay of Bengal: A study to assess the role of transport from southern India and marine regions during September–October 2002 by L.K. Sahu; S. Lal; S. Venkataramani (4633-4645).
Mixing ratios of O3 and some related trace species like CO, CH4 and C2–C4 hydrocarbons were measured in the marine boundary layer (MBL) over the Bay of Bengal during September and October 2002. Air parcels having different and consequently variable compositions were encountered during the campaign. The strength of variability is reflected in their observed ranges; for O3 (13–43 ppbv), CO (108–210 ppbv), CH4 (1.67–1.86 ppmv), ethane (376–913 pptv) and acetylene (16–420 pptv). In general, continental influenced air masses dominated over the northern region while the cleaner marine air masses prevailed over the southern region of the Bay of Bengal. Ozone, CO, CH4 and some anthropogenic NMHCs showed significant latitudinal gradients, while short-lived species like ethene, propene and butanes did not show any significant gradients. However, the latitudinal gradients in O3 and CO are observed to be lower and much higher in CH4 over the Bay of Bengal compared to those observed during the Indian Ocean Experiment (INDOEX) 1998 and 1999 campaigns. Study of wind fields, back-trajectories and C2H2/CO ratios support role of advection in the observed distribution of trace gases over the Bay of Bengal.
Keywords: Bay of Bengal; Trace gases; NMHCs; Transport; India;
Comment on “fully coupled ‘online’ chemistry within the WRF model,” by Grell et al., 2005. Atmospheric Environment 39, 6957–6975 by Mark Z. Jacobson (4646-4648).