Atmospheric Environment (v.36, #4)

In this study, air-pollutant concentrations at a number of stations are analyzed during a severe air-pollution episode in Hong Kong on 29 and 30 December 1999. It is found that high levels of NO x , RSP and SO2 emitted from vehicles and the power plants in Hong Kong are mainly responsible for this episode. O3 concentrations are much lower than the background values, indicating the chemical scavenging of O3 caused by its precursor emissions from traffic and other sources in Hong Kong. Under the calm synoptic conditions, air-pollutant patterns are governed by the interaction of local circulations, the complex topography and the stabilities. During daytime, air pollutants are redistributed by several sea-breeze circulations developing in Hong Kong from different directions. Meanwhile, several convergence zones created by the different wind systems are found to be situated over some urban areas and new towns in the western part of Hong Kong. This significantly traps air pollutants in these locations. During the nighttime, the stably stratified flow over the complex topography leads to complex airflow patterns with light winds, consequently leading to pollutant accumulations. These mechanisms explain the main features of temporal and spatial variations of air-pollutant concentrations in Hong Kong.
Keywords: Air-pollution episode in Hong Kong; Sea–land breezes; Air-pollutant concentrations; Convergence zones;

Temporal variations in surface ozone at Thumba (8.6°N, 77°E)-a tropical coastal site in India by P.R Nair; D Chand; S Lal; K.S Modh; M Naja; K Parameswaran; S Ravindran; S Venkataramani (603-610).
Surface measurements of ozone and meteorological parameters are made at a tropical coastal site, Thumba (8.6°N, 77°E, 2 m) in India from April 1997 to March 1998. Ozone shows a diurnal variation with daytime higher levels and a sharp change in its values during evening time. The evening time change in ozone values with a secondary peak is found to be due to change in wind pattern from sea-breeze to land-breeze at this site. This secondary peak in ozone is weakest during monsoon period. A detailed study of the meteorological parameters shows that during nighttime, polluted air from land side moves to the nearby marine region relatively increasing the levels of ozone and precursor gases. Observations show that the onset time of daytime ozone increase and its rates are related with each other. If onset time of ozone increase is early, its increase rate is slower and vice versa. Maximum ozone levels are observed to be during March, probably due to intense photochemical production. However, this is different when compared to other Indian site like Ahmedabad, where maximum ozone levels are observed during late autumn and early winter. Monthly average ozone levels are observed to be very low (in the range of 13–22 ppbv) at Thumba.
Keywords: Ozone; Coastal site; Boundary layer; Sea-breeze; Land-breeze and photochemistry;

Source identification of Malaysian atmospheric polycyclic aromatic hydrocarbons nearby forest fires using molecular and isotopic compositions by Tomoaki Okuda; Hidetoshi Kumata; Mohamad Pauzi Zakaria; Hiroshi Naraoka; Ryoshi Ishiwatari; Hideshige Takada (611-618).
We report measurements of molecular and carbon isotopic compositions of Malaysian atmospheric polycyclic aromatic hydrocarbons (PAHs) in smoke haze from the 1997 Indonesian forest fire. Comparison of the carbon isotopic compositions (δ 13C) of individual PAHs from the smoke haze, with those from other PAHs sources (soot collected from gasoline and diesel vehicle muffler, woodburning smoke), enables us to discriminate among the diverse sources of atmospheric PAHs. Soot PAHs extracted from gasoline and diesel vehicles show heavy isotopic signatures with a large inter-species δ 13C variation from −12.9‰ to −26.6‰, compared to soot PAHs extracted from woodburning smoke which are isotopically light, and have a small inter-species δ 13C variation from −26.8‰ to −31.6‰. Values from −17.7‰ to −27.9‰ were obtained for the corresponding PAHs extracted from the smoke haze, indicating that they are derived mainly from automotive exhaust. Molecular and isotopic compositions of PAHs extracted from smoke haze were similar to those extracted from non-haze aerosol. Quantitative estimation shows that woodburning contribution to Malaysian atmospheric PAHs ranges from 25% to 35% with no relation to haze intensity, while automotive contribution ranges from 65% to 75%. These results suggest that the major contributor of PAHs in Malaysian air is automotive exhaust whether smoke haze is observed or not.
Keywords: Aerosols; Atmospheric PAHs; Compound-specific δ 13C; Source identification; Tropic forest fires;

Spatial distribution of wet deposition of nitrogen in South Korea by Soon-Ung Park; Young-Hee Lee (619-628).
A method is developed to estimate wet deposition of nitrogen in a 11×14 km (0.125°Lon.×0.125°Lat.) grid scale using the precipitation chemistry monitored data at 10 sites scattered over South Korea supplemented by the routinely available precipitation rate data at 65 sites and the estimated emissions of NO2 and NH3 at each precipitation monitoring site. This approach takes into account the contributions of local NO2 and NH3 emissions and precipitation rates on wet deposition of nitrogen. Wet deposition of nitrogen estimated by optimum regression equations for NO3 and NH4 + derived from annual total monitored wet deposition and that of emissions of NO2 and NH3 is incorporated to normalize wet deposition of nitrogen at each precipitation rate class, which is divided into 6 classes. The optimum regression equations for the estimation of wet deposition of nitrogen at precipitation monitoring sites are developed using the normalized wet deposition of nitrogen and the precipitation rate at 10 precipitation chemistry monitoring sites. The estimated average annual total wet depositions of NO3 and NH4 + are found to be 260 and 500 eq ha−1  yr−1 with the maximum values of 400 and 930 eq ha−1  yr−1, respectively. The annual mean total wet deposition of nitrogen is found to be about 760 eq ha−1  yr−1, of which more than 65% is contributed by wet deposition of ammonium while, the emission of NH3 is about half of that of NO2, suggesting the importance of NH3 emission for wet deposition of nitrogen in South Korea.
Keywords: NO2 emission; NH3 emission; Precipitation rate; South Korea; Optimum regression equation; Deposition modeling;

Diurnal and seasonal variations in carbon dioxide and methane fluxes between Sundarban biosphere and atmosphere were measured using micrometeorological method during 1998–2000. Study of the diurnal variation of micrometeorological conditions in the atmosphere was found to be necessary to determine the duration of neutral stability when flux estimation was reliable. Neutral stability of the atmosphere occurred in the limited micrometeorological conditions, when friction velocity ranged between 0.360 and 0.383  m s −1 . The value of drag coefficient (1.62–20.6)×103 obtained at variable wind speed could be deemed specific for this particular surface. 58.2% drop of carbon dioxide and 63.4% drop of methane in the atmosphere at 1  m height were observed during day time, between dawn and early evening. Diurnal variations in methane and carbon dioxide mixing ratios showed a positive correlation with Richardson's number (Ri). This environment acted as a net source for carbon dioxide and methane. The mixing ratios of methane were found to vary between 1.42 and 2.07  ppmv , and that of carbon dioxide, between 324.3 and 528.7  ppmv during the study period. The biosphere–atmosphere flux of carbon dioxide ranged between −3.29 and 34.4  mg m −2   s −1 , and that of methane, between −4.53 and 8.88  μg m −2   s −1 . The overall annual estimate of carbon dioxide and methane fluxes from this ecosystem to atmosphere were estimated to be 694  Tg yr −1 and 184  Gg yr −1 , respectively. Considerable variations in mixing ratios of carbon dioxide and methane at the NE coast of Bay of Bengal were observed due to the seasonal variations of their fluxes from the biosphere to the atmosphere. The composition was inferred by fitting model prediction to measurements.
Keywords: Trace gases; Micrometeorology; Box model; Mangrove forest; Sundarban;

A systematic method combining water and diluted-acid extractions has been developed for the manifold evaluation of soluble and insoluble fractions in ambient aerosol. The pre-washed regenerated cellulose membrane filter was used as a collection medium of a low-volume air sampler. The collection time of 7–14 days was required to obtain the sample amounts enough for the systematic analysis. Simple and efficient extraction procedures using the filtration of water and 0.1 M hydrochloric acid were recommended in order to obtain the information about the dissolution behaviors of various elements in the aerosol. Soluble components in both the extracts were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) and ion chromatography (IC). These extraction procedures were also preferred to prepare thin-layer specimens suitable to the succeeding X-ray fluorescence spectrometry (XRF) for insoluble components. Elemental compositions of the extraction residues were conveniently determined by the XRF calibrated with thin-layer standard specimens prepared with activated carbon. The determination of the 17 representative elements (Na, Mg, Al, Si, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Br, Pb) in these three fractions from an aerosol sample was performed rapidly within 4 h. The proposed systematic method was applied to PM2.5 and PM10 aerosol samples collected in Kofu City, Central Japan, and the enrichment behaviors of various elements and their source apportionment such as soil, anthropogenic substances and vehicle exhaust particulates could be demonstrated by the present method.
Keywords: Water and diluted-acid extractions; Extraction residue; Inductively coupled plasma atomic emission spectrometry; Ion chromatography; X-ray fluorescence spectrometry;

Influence of benzene emission from motorcycle on Bangkok air quality by Shing Tet Leong; S Muttamara; Preecha Laortanakul (651-661).
This study investigated the influence of benzene concentration from motorcycle exhaust emissions on ambient air quality in Bangkok Metropolitan Region (BMR). Measurement of benzene concentration in exhaust emissions is performed on a standard test driving cycle through which each motorcycle to be tested is driven. The test result revealed that average benzene concentrations in exhaust emission for the test motorcycles ranged from 3.02 to 109.68 mg/m3. The finding also indicated that two-stroke motorcycles emitted five times more benzene than that of four-stroke motorcycles. Four air monitoring sites were strategically established to determine the relationship between average benzene concentrations with different traffic configurations in each traffic zone of BMR during peak/non-peak hours, day/night times and weekday/weekend. The shape of the curve for benzene level usually shows two peaks corresponding to the morning and evening traffic rush or commuter rush hours. The finding shows that the mean concentrations for benzene in all monitoring stations in the ambient air for peak hours (07:00–09:00 and 16:00–18:00 h) ranged from 15.1 to 42.4 μg/m3. For non-peak hour (11:30–15:00 h), benzene levels were found in the range 16.3–30.9 μg/m3. It is observed that higher levels of benzene are found among roadside stations with slow moving traffic while lower levels are found among roadside stations with fast traffic movement. Additional factors such as temperature, wind speed, rainfall, etc. are also considered in this study to determine the relationship between traffic conditions and ambient benzene levels.
Keywords: Benzene; Carcinogen; Driving cycle; Motorcycle; Peak hour; Thailand;

The concentrations of total gaseous mercury (Hg) were determined from an urban area between two different time periods of the late 1980s and the late 1990s and compared to evaluate the mechanisms regulating Hg distribution over a decadal period. Because of time gap and the associated changes in source/sink relationships, the observed concentration levels of Hg were remarkably different between the two periods. The results showed that the Hg levels in the former period were averaged to be 14.4±9.56 ng m−3 (N=2714), while the latter period was recorded at approximately three-fold reduced values of 5.34±3.92 ng m−3 (N=2576). Using the measurement data for the two independent periods, we were able to describe the basic features of Hg distribution that correspond to each time period. When inspected over a 24 h scale, two contrasting patterns emerged for the two time periods. The former was characterized by enhanced concentration levels during daytime, but the latter with relative depletion during daytime. The results of the two periods, when inspected over seasonal scale, showed many similarities and dissimilarities simultaneously. In order to analyze the factors affecting Hg distributions of each period, we conducted correlation analysis on the data groups divided both diurnally and seasonally. Results of these analyses consistently indicate that correlation patterns may be associated with the factors regulating the diurnal variability of Hg. The data for the late 1980s consistently indicate the presence of a single dominant source process that can be represented by the use of coal. However, the patterns described for those of the late 1990s suggest that the sources of Hg be tightly tied up with the general sources of air pollution that can lead to the degradation of urban air quality. In addition, we suspect that notable shifts in meteorological conditions between the two periods might also have been conducive to changes in Hg concentration levels to a certain extent.
Keywords: Temporal; Anthropogenic; Urban; Residence time; Source signatures; Mercury;

A comprehensive, spatially resolved (0.25°×0.25°) fossil fuel consumption database and emissions inventory was constructed, for India, for the first time. Emissions of sulphur dioxide and aerosol chemical constituents were estimated for 1996–1997 and extrapolated to the Indian Ocean Experiment (INDOEX) study period (1998–1999). District level consumption of coal/lignite, petroleum and natural gas in power plants, industrial, transportation and domestic sectors was 9411 PJ, with major contributions from coal (54%) followed by diesel (18%). Emission factors for various pollutants were derived using India specific fuel characteristics and information on combustion/air pollution control technologies for the power and industrial sectors. Domestic and transportation emission factors, appropriate for Indian source characteristics, were compiled from literature. SO2 emissions from fossil fuel combustion for 1996–1997 were 4.0 Tg SO2  yr−1, with 756 large point sources (e.g. utilities, iron and steel, fertilisers, cement, refineries and petrochemicals and non-ferrous metals), accounting for 62%. PM2.5 emitted was 0.5 and 2.0 Tg yr−1 for the 100% and the 50% control scenario, respectively, applied to coal burning in the power and industrial sectors. Coal combustion was the major source of PM2.5 (92%) primarily consisting of fly ash, accounting for 98% of the “inorganic fraction” emissions (difference between PM2.5 and black carbon+organic matter) of 1.6 Tg yr−1. Black carbon emissions were estimated at 0.1 Tg yr−1, with 58% from diesel transport, and organic matter emissions at 0.3 Tg yr−1, with 48% from brick-kilns. Fossil fuel consumption and emissions peaked at the large point industrial sources and 22 cities, with elevated area fluxes in northern and western India. The spatial resolution of this inventory makes it suitable for regional-scale aerosol-climate studies. These results are compared to previous studies and differences discussed. Measurements of emission factors for Indian sources are needed to further refine these estimates.
Keywords: SO2; PM2.5; Carbonaceous aerosols; Fly ash; Power plants; Brick-kilns; INDOEX;

A spatially resolved biomass burning data set, and related emissions of sulphur dioxide and aerosol chemical constituents was constructed for India, for 1996–1997 and extrapolated to the INDOEX period (1998–1999). Sources include biofuels (wood, crop waste and dung-cake) and forest fires (accidental, shifting cultivation and controlled burning). Particulate matter (PM) emission factors were compiled from studies of Indian cooking stoves and from literature for open burning. Black carbon (BC) and organic matter (OM) emissions were estimated from these, accounting for combustion temperatures in cooking stoves. Sulphur dioxide emission factors were based on fuel sulphur content and reported literature measurements. Biofuels accounted 93% of total biomass consumption (577 MT yr−1), with forest fires contributing only 7%. The national average biofuel mix was 56 : 21 : 23% of fuelwood, crop waste and dung-cake, respectively. Compared to fossil fuels, biomass combustion was a minor source of SO2 (7% of total), with higher emissions from dung-cake because of its higher sulphur content. PM2.5 emissions of 2.04 Tg yr−1 with an “inorganic fraction” of 0.86 Tg yr−1 were estimated. Biomass combustion was the major source of carbonaceous aerosols, accounting 0.25 Tg yr−1 of BC (72% of total) and 0.94 Tg yr−1 of OM (76% of total). Among biomass, fuelwood and crop waste were primary contributors to BC emissions, while dung-cake and forest fires were primary contributors to OM emissions. Northern and the east-coast India had high densities of biomass consumption and related emissions. Measurements of emission factors of SO2, size resolved aerosols and their chemical constituents for Indian cooking stoves are needed to refine the present estimates.
Keywords: Biofuels; Forest biomass; Black carbon; Organic matter; INDOEX;

Modeling the diurnal variability of effective albedo for cities by David J. Sailor; Hongli Fan (713-725).
As applied to urban domains, traditional representations of surface albedo do not adequately account for the complex radiative exchange within the urban canopy. In this paper, we present a simple radiation model that takes into account the diurnal variation of short-wave radiation, including the effects of surface shading and radiation exchange among surfaces within the urban canopy. The model has been validated using prior observational studies and used to calculate the time-dependent effective short-wave reflectivity of hypothetical and case study urbanized grid cells, as well as the daily energy-weighted average of these parameters. Monte Carlo style simulations for four distinct urban land use categories indicate that the nadir-view albedo (NVA) typically underestimates daily solar radiative loads by 11–22%, depending upon the land use. We have also found that fairly detailed land-use classification schemes introduce large uncertainties in NVA. In fact, the uncertainty in albedo values for any urban land use category is comparable to the albedo variability across the various urban land use classifications. Furthermore, the magnitude of the diurnal variability of effective albedo for cities is large enough that neglecting it could adversely impact the ability to resolve the energy balance and circulation patterns associated with the urban heat island.
Keywords: Albedo; Radiation; Energy balance; Urban heat island; Mesoscale meteorology;

To investigate if air pollution generated in the Himalayan foothills reached higher elevations, a sequence of surface meteorological and condensation nucleus (CN) measurements were made between October 1995 and May 1996. Measurements were made in the Kathmandu valley of the foothills, in the Dudh Kosi valley of the eastern Himalayas and at the base of Mt. Everest in Nepal and Tibet. The Kathmandu valley measurements revealed a semi-diurnal variation of CN and moisture in the mountain-valley wind system and a reduction of both in strong afternoon convection we call the “Kathmandu chimney”. The air was polluted at all times in the valley. The Dudh Kosi measurements revealed a diurnal variation in CN and moisture; both were drawn into the valley in the strong afternoon valley wind and cleaner and drier air flowed into the valley in the nighttime mountain wind. The air was unpolluted in the mornings and frequently polluted in the afternoon and evenings; some of the evening pollution was from local sources. The CN concentrations in Tibet were smaller than in Nepal at the same elevation due dilution in the deep afternoon convective boundary layer in Tibet; there also may be a “Tibetan chimney”. Evidence is presented for trans-Himalayan pollution transport: a 7-h pollution episode originating in Nepal was advected into Tibet and a 18-h episode originating in Tibet was advected into Nepal.
Keywords: Mountain-valley winds; Air pollution in complex terrain; Himalayan weather; Condensation nucleus measurements; Air pollution and convection;

A lifecycle assessment to estimate greenhouse gas emissions in Australia from the paper cycle is summarised. The greenhouse gas emissions from paper in Australia in 1999/2000 were estimated to be 12.1 million tonnes (Mt) of CO2 equivalent. Nearly half of this amount consisted of CH4 emissions from landfilled waste paper. Various waste management options were modelled to investigate the greenhouse impact of a tonne of paper over its whole lifecycle. Options that keep paper out of landfills significantly reduce greenhouse emissions, waste-to-energy recovery being most effective. Recycling is also beneficial, and is of particular interest from a management perspective because it can be controlled by the pulp and paper industry. These findings can be extended to other wood-based and organic wastes.
Keywords: Methane; Carbon dioxide; Recycling; Landfill; Energy recovery; Bioreactor;

Fuel-cycle greenhouse gas emissions from alternative fuels in Australian heavy vehicles by Tom Beer; Tim Grant; David Williams; Harry Watson (753-763).
This paper quantifies the expected pre-combustion and combustion emissions of greenhouse gases from Australian heavy vehicles using alternative fuels. We use the term exbodied emissions for these full fuel-cycle emissions. The fuels examined are low sulfur diesel (LSD), ultra-low sulfur diesel (ULS), compressed natural gas (CNG), liquefied natural gas (LNG), liquefied petroleum gas (LPG), ethanol (from lignocellulose), biodiesel and waste oil. Biodiesel and ethanol have the lowest exbodied greenhouse gas emissions (in grams greenhouse gases per kilometre travelled). Biodiesel reduces exbodied greenhouse gas emissions from 41% to 51% whereas ethanol reduces emissions by 49–55%. In fact, both emit larger quantities of CO2 than conventional fuels, but as most of the CO2 is from renewable carbon stocks that fraction is not counted towards the greenhouse gas emissions from the fuel. The gaseous fuels (LPG, CNG) come next with emissions that range from 88% to 92% of diesel. The emissions of greenhouse gases from diesel are reduced if waste oil is used as a diesel extender, but the processing energy required to generate LSD and ULS in Australia increase their greenhouse gas emissions compared to diesel fuel. The extra energy required liquefy and cool LNG means that it has the highest exbodied greenhouse gas emissions of the fuels that were considered.
Keywords: Alternative fuels; Greenhouse gas emissions; Life-cycle; Heavy vehicles; Australian emissions;

The fractionation of atmospheric sea-salt has been investigated by glaciochemical analysis of the sea-salt deposited on the snow covering the small ice cap of James Ross Island, Antarctic Peninsula, at an elevation of 1640 m. The data show that, generally, but not always, the sea-salt deposited at this location most likely originates directly from seawater, as is the case at lower latitudes. It is found that the original chemical composition of the sea-salt aerosol is significantly modified, in particular by the reaction of sea-salt particles in the atmosphere with acid species. A ternary diagram (sodium, chloride, sulfate) is used to enlighten the involved modification processes. The study points out the frequent formation of HCl in the regional atmosphere.
Keywords: Antarctica; Sea-salt; Aerosol; Fractionation; Hydrogen chloride; Snow;