Atmospheric Environment (v.34, #4)

Precipitation chemistry in East Asia by Shin-ichi Fujita; Akira Takahashi; Jian-Hua Weng; Lian-Fen Huang; Hui-Kang Kim; Cheng-Kang Li; Frank T.C. Huang; Fu-Tien Jeng (525-537).
The chemical composition of precipitation in East Asia was analyzed on the basis of the results of cooperative monitoring performed during the period from 1992 to 1993. The wet deposition of soluble ions was characterized by two major factors; the geographical distribution of precursor production through natural and anthropogenic activities, and the meteorological conditions such as wind system and rainfall pattern due to the Asian monsoon. Although northeastern China had the largest anthropogenic emission source, precipitation with relatively high pH value was observed. At islands in the northern Pacific far from major anthropogenic emission sources, precipitation with relatively low pH value was observed. It was suggested that ammonia and calcium were constantly produced in the continent, and that the higher concentrations of these bases in the atmosphere were incorporated into precipitation elements and neutralized the acidity due to H2SO4 and HNO3 from fossil fuel combustion. The ratio of [nssCa2++NH4 +]/[nssSO4 2−+NO3 ] in precipitation was highest on the continent, moderate in the Korean Peninsula and the Japanese Islands, and lowest in the northern Pacific; in other words, this ratio decreased as the distance from the continent increased. In the central region of East Asia, which is affected by both continental cold, dry air masses and subtropical warm, humid air masses, the frequency distribution of pH of precipitation showed a bimodal pattern in which unimodal patterns of northern China and that of the Japanese Islands were superimposed. The wet deposition of nssSO4 2−, NO3 , nssCa2+, and NH4 + showed relatively small differences between the sites, while that of Na+ and Cl, relatively large differences between the sites, reflecting the field of ionic concentration and amount of precipitation in East Asia.
Keywords: Acid rain; Precipitation chemistry; Wet deposition; Emission; East Asia;

A numerical investigation of urban influences on local meteorological conditions during the Bhopal gas accident by Maithili Sharan; S.G Gopalakrishnan; R.T McNider; M.P Singh (539-552).
A three-dimensional mesoscale model () was used to investigate possible urban effects on the prevailing meteorological conditions during the Bhopal gas leak. A distinct urban heat island circulation was formed when a gradient of 6°C exists between the city area of Bhopal and the rural area and when the geostrophic wind at 850 mb level is very weak (i.e., 1 m s−1). However, when the wind speed at 850 mb level was increased to the observed speed of 3 m s−1, the urban heat island circulation disappeared. The modelling experiments indicate that under the prevailing synoptic conditions, the urban circulation should not have had a major influence on the local meteorological conditions during the Bhopal gas accident.
Keywords: Bhopal gas leak; Urban circulation; Mesoscale model; Meteorological conditions; Geostrophic wind;

Ozone and CO were simultaneously measured for 17 days at the summit of Mt. Fuji (3776 m above sea level) in summer 1997. A classification of air mass origins based on backward trajectory analysis showed that both ozone and CO exhibit minimum concentrations in the air mass originating in southeast Asia, probably due to photochemical destruction during transport over the ocean. Both ozone and CO show maximum concentrations in the air mass originating in northeast Asia, reflecting background concentrations. Air mass groups transported long range from the Pacific, southeast Asia, and northeast Asia exhibit positive correlation between ozone and CO, while the air mass group staying around Japan that was thought to include fresh anthropogenic pollution negatively correlated. Diurnal variation of ozone in the air mass from the Pacific and southeast Asia (relatively clean and humid air) shows that ozone is likely to be photochemically destroyed in the air uplifted by valley winds at the summit in the daytime. Both diurnal variations of CO and ozone show evening enhancements in the case that the air at the summit passed over the Nagoya urban and industrial area before arriving at the summit. Thus, the polluted air is likely to be lifted up by convective plumes in the Nagoya area around noon, being transported with diffusion to Mt. Fuji in the evening.
Keywords: Tropospheric ozone; Carbon monoxide; Correlation; Long-range transport; Diurnal variation;

Daily wet precipitations were collected at nine stations in South Korea from May 1996 to April 1998 and analyzed for pH, electrical conductivity and major ions; SO4 2−, NO3 , Cl, NH4 +, Ca2+, Na+, Mg2+ and K+. The volume-weighted mean concentrations of NO3 and non-seasalt SO4 2− were 19.3 and 43.0 μeq l−1, respectively, which were comparable to Northeast America and Central Europe. However, the level of H+ was found to be significantly lower as a result of neutralization by ammonia and calcium containing compounds. Although the pH of individual precipitations fluctuated excessively with a wide range from 3.4 to 8.0, the annual mean value ranged from 4.6 to 4.8 without area variation. With the exception of the seasalt ions, no distinct spacial variations in ion composition were observed. On the other hand, seasonal variations were evident. Annual wet deposition was estimated and compared to that in East Asian countries and other continents.
Keywords: Acid rain; pH; Neutralization; East Asia; Seasonal variation;

Volatile organic compounds (VOC), more specifically, non-methane volatile organic compounds (NMVOC) play a critical role in the atmospheric chemistry. NMVOC, through complex photochemical reactions, contribute to the formation of toxic oxidants, such as tropospheric ozone and PAN, which are injurious to health and highly phytotoxic. Certain NMVOC have been shown to be highly toxic, mutagenic and carcinogenic. NMVOC are receiving increasing attention in the west on account of their implication for human health and air quality. On the other hand, information on NMVOC in India and other developing countries is not available. As a result, appreciation of potential threat from NMVOC in relation to air quality and public health is sadly lacking among planners and policy makers. The paper deals with the estimation of total NMVOC at 13 sites in the urban environment of Delhi during November 1994 to June 1995. An inexpensive, labour intensive manual sample collection device was used and the air samples were analysed using GC-FID. The results show that the amount of NMVOC in the ambient environment of Delhi varied between 1.3 and 32.5 ppmv exhibiting wide temporal and seasonal variation. NMVOC levels mostly peaked at 0900 h, which coincide with the peak traffic hour. The implications of NMVOC build-up in the urban atmosphere are obvious for air quality. The results of this preliminary study make out a strong case for developing a regular monitoring programme for NMVOC in the urban environment of Delhi as well as in other major cities in the region.
Keywords: Air quality; Non-methane volatile organic compounds (NMVOC), Ozone; Volatile organic compounds (VOC);

Principal components analysis and average linkage clustering procedure are used to automatically classify seasonal distinctive synoptic categories based on 6-hourly surface meteorological data for Hong Kong. This procedure is able to identify the specific categories exhibiting particularly high mean pollution concentrations and producing high frequency of severe pollution events. It is found that high SO2 and NO x concentrations are usually associated with the certain spring and summer air masses with moderate to strong southwesterly or westerly winds as well as related to the autumn and winter synoptic categories with light northerly or easterly winds. This procedure has a potential to forecast air pollution concentrations, which could be achieved through predicting the arrival of the most polluted synoptic categories.
Keywords: Air pollution; Synoptic climatology; Climate classification; Hong Kong;

Determination of domain for diagnostic wind field estimation in Korea by Jin Young Kim; Young Sung Ghim; Yong Pyo Kim; Donald Dabdub (595-601).
A diagnostic routine is applied to estimate wind fields for two coastal areas with mountains in Korea. The reliability of the predicted wind fields is assessed by calculating the maximum differences of wind speed and direction between two successive estimations by increasing the size of the estimation domain over the target domain. The differences decrease and stabilize after a critical increment to produce an optimum domain size used to estimate wind fields. Although a larger radius of influence and a larger grid size could increase the stability of convergence, they smooth the predicted wind field and decrease the resolution. The study also reveals that the estimated wind field shows larger differences from the wind field obtained with all stations available in the country, at higher mountains along the boundaries beyond which stations would be added if larger domains are employed.
Keywords: Diagnostic wind field estimation; Sensitivity analysis; Distribution of stations; Boundary topography;

Using a method developed by Qiu (Qiu, J., 1998. A method to determine atmospheric aerosol optical depth using total direct solar radiation. J. Atmos. Sci. 55, 734–758), 0.75 μm aerosol optical depths at five meteorological observatories in north China during 1980–1994 are retrieved from global direct solar radiation, and variation characteristics of the depths and visibility are analyzed. These observatories are located in the cities of Wulumuqi, Geermu, Harbin, Beijing and Zhengzhou. It is found that during 1980–1994 the aerosol optical depths show an increasing trend at all five sites. During winter the trend is stronger. In winter at Beijing and Wulumuqi, the depth increased by a factor of about two in 15 years. Pollution caused due to the burning of fossil fuel is the main cause of the change. In spring at Geermu the depth is larger and its increase is the quickest among the four seasons, mainly due to desert dust events. The Pinatubo volcanic eruption in 1991 had a significant influence on the aerosol optical depth. The yearly averaged depths over five sites in 1992 after the eruption increased by 0.068 to 0.212, compared to those in 1990, while from 1992 to 1994 they generally show a decreasing trend. In some cities such as Zhengzhou and Geermu, both visibility and optical depth show an increasing trend during 1980–1994, a possible reason for this is that the aerosol particle vertical distribution shifts up in the troposphere. At Geermu, Harbin, Beijing and Zhengzhou, optical depths in summer are larger, which may be because of the growth of aerosol particles growing in the moist summer. Apart from Geermu, at the other four sites visibility in winter is smaller, especially at Wulumuqi and Harbin. At Harbin, visibility in summer is about twice larger than that in winter, but the difference between depths is small, implying the turbid lower troposphere in winter and the larger extinction coefficient in the upper troposphere during summer.
Keywords: Direct solar radiation; Visibility; Aerosol; Optical depth; Pinatubo effect;

Fifteen polycyclic aromatic hydrocarbons (PAHs) were measured simultaneously in the indoor and outdoor air of 14 homes in the Taipei urban area in both summer and winter seasons. It was indicated that indoor and outdoor geometric mean PAH concentrations were 267 and 209 ng m−3, respectively. In addition, it was observed that indoor PAH concentrations generally exceeded the corresponding outdoor PAH concentrations. Moreover, the median value of indoor/outdoor PAH ratios was observed to be 1.23 which might demonstrate that there was no presence of significant indoor PAH sources in this subtropical region. Concerning PAH seasonal variations, the observed lower winter/summer ratios might be related to the absence of domestic heating in residential environments. With regard to PAH compositions, the most abundant PAH found indoors was naphthalene. Fluorene and phenanthrene were the second and third highest concentrations found indoors and outdoors. In incensed homes, PAHs could be contributed mainly to incense burning as well as background sources might be the largest contributor to PAHs in non-incensed homes.
Keywords: Indoor air quality; PAH; Benzo (a) pyrene; Indoor–outdoor comparison; Urban;

Analysis of precipitation chemistry at a rural site in Hiroshima Prefecture, Japan by Sinya Seto; Mayumi Oohara; Yukoh Ikeda (621-628).
Event basis measurements of precipitation chemistry at Shobara, the rural area of the northeastern part in Hiroshima Prefecture in Japan, during the period 1984–1988, were assessed for determining the sources of major ions, and for understanding the relation between ionic concentrations and synoptic meteorological situations. Seasonal patterns of the volume-weighted mean concentrations for major ions except H+ could be characterized by winter maxima and summer minima. Principal component analysis was performed on monthly ionic deposition. Varimax rotated three principal components accounting for approximately 90% of the total variance in the data set, could be interpreted to be acid, seasalt and soil. From back-trajectories for an event using 850 hPa winds, it was found that the volume-weighted mean concentration of non-sea-salt (nss−) SO2− 4 for the air-mass transported from the northern part of Asian Continent was highest, and that the majority of high nss-SO2− 4 concentrations for an event were observed for the continental air-mass under the condition of light precipitation amount.
Keywords: Precipitation chemistry; Acidic precipitation; Wet deposition; Sulfate; Principal component analysis; Trajectory analysis;

Results from a year long programme of measuring ground-level concentration of NO x at 19 important traffic intersection points within the city of Calcutta have been presented. Fortnightly measurements were made with a set of three passive samplers along with a control deployed at each of the sites.Results indicate that the NO x concentration level has a seasonal variation. Maximum average concentration of 222 μg m−3 was observed during winter and a minimum average concentration of 55 μg m−3 was observed during peak monsoon.
Keywords: NO x concentration; Traffic; Passive sampler; Air pollution; Calcutta;

Biomass burning influences on the composition of the remote South Pacific troposphere: analysis based on observations from PEM-Tropics-A by H.B Singh; W Viezee; Y Chen; J Bradshaw; S Sandholm; D Blake; N Blake; B Heikes; J Snow; R Talbot; E Browell; G Gregory; G Sachse; S Vay (635-644).
Airborne, in situ measurements from PEM-Tropics-A (September/October 1996) are analyzed to show the presence of distinct pollution plumes in the middle-tropical troposphere of the remote South Pacific (10–30°S). These elevated plumes cause a relative maximum at about 5–7 km altitude in the vertical distribution of primary and secondary species characteristic of fuel combustion and biomass burning (CO, C2H2, C2H6, CH3Cl, PAN, O3). Similar plumes were also observed at mid-latitudes in the middle troposphere during three flights east of New Zealand (40–45°S). In all, pollution plumes with CO larger than 100 ppb were observed 24 times on seven separate flight days south of the equator. The observed plumes were frequently embedded in very dry air. Ten-day back trajectory analysis supports the view that these originated from the biomass burning regions of South Africa (and South America) and were transported to the South Pacific along long-distance subsiding trajectories. The chemical composition of the southern Pacific troposphere analyzed from the PEM-Tropics-A data is compared with data from the tropical regions of the northern Pacific (PEM-West-A) and southern Atlantic (TRACE-A) during the same Sept/Oct time period. Sizable perturbations in the abundance of ozone and its key precursors, resulting from the transport of pollution originating from biomass burning sources, are observed in much of the Southern Hemispheric troposphere.
Keywords: Trace chemicals; Biomass burning pollution; Remote atmospheres;

Monoterpene and isoprene emissions from 15 Eucalyptus species in Australia by Congrong He; Frank Murray; Tom Lyons (645-655).
Monoterpene and isoprene emission rates of 15 Eucalyptus species were measured using an air exchange chamber technique and GC-FID analysis. The normalised monoterpene emission rates (leaf temperature 30°C) of these Eucalyptus species ranged from zero for E. forrestiana to 5.4±2.2 μg g−1  h−1 (or 871±33 μg m−2  h−1) for E. globulus. The dominant monoterpene compounds emitted from these Eucalyptus species were α-pinene, 1,8-cineole, β-pinene and limonene. The normalised isoprene emission rates (leaf temperature 30°C, PAR flux 1000 μmol m−2  s−1) ranged from 5.3±1.6 (E. botryoides) to 69±34 μg g−1  h−1 (E. globulus) or from 0.74 (E. cladocalyx) to 9.5 mg m−2  h−1 (E. rudis). Based on monoterpene emission rate data from four Eucalyptus species (E. globulus, E. robusta, E. rudis, and E. sargentii), there were clear exponential relationships between leaf temperature and monoterpene emission rate for these Eucalyptus species. The mean exponential value (β value) of the four Eucalyptus species was 0.103±0.012 K−1.
Keywords: Biogenic emission; Hydrocarbons; Photochemical smog; Air pollution;

Emissions from in-use lawn-mowers in Australia by M.W. Priest; D.J. Williams; H.A. Bridgman (657-664).
Concern over the levels of pollutants emitted from small engines has led to recent legislation in the United States that regulates exhaust emissions from lawn and garden equipment. Particular attention has focused on the high levels of hydrocarbons emitted by these engines. The present study establishes emission factors for lawn-mowers in use in Australia. The estimates were calculated on the basis of a series of controlled emission tests conducted on commonly used lawn-mowers. Ten two-stroke and six four-stroke lawn-mower engines were operated under simulated power requirements while fuel usage and gas emissions were monitored. Fuel consumption rates from the tests were compared to those ascertained under actual mowing conditions in field tests conducted on 19 two-stroke and ten four-stroke lawn-mowers. Basic emission factors were established for CO, CO2, CH4, NMHC and NO x , and combined with data on machine population and annual usage collected in a survey of lawn care practices and lawn-mower usage conducted in the Newcastle area. When compared to transport sources in the Newcastle study region, lawn-mowers contribute 5.2 and 11.6% of CO and NMHC emissions, respectively.
Keywords: Lawn-mowers; Carbon monoxide; Hydrocarbons; Nitrogen oxides; Two-stroke; Four-stroke; Fuel consumption;

Wet deposition of trace metals to a remote site in Fiordland, New Zealand by Michael J.R. Halstead; Robert G. Cunninghame; Keith A. Hunter (665-676).
Cd, Cu, Fe, Mn, Pb, Zn, Ca, Mg, Na, pH, and 210 Pb were determined in rainwater collected at Paradise, a remote site in Fiordland, New Zealand, to evaluate sources and fluxes of atmospheric trace metals in the NZ region of the South Pacific westerlies. Individual rain events were sampled using rigorous trace metal clean protocols during 1993–1995. Air-mass trajectories showed an Australian and Southern Ocean influence on most samples. Ca, Mg, and Na were highly correlated with each other, over 2–3 orders of magnitude, and had a sea-salt aerosol source. Most of the Fe was not soluble in 0.03 M nitric acid after 48 h, suggesting low bioavailability after deposition to the ocean, whereas most of the Zn was soluble. Mean trace metal concentrations were similar to those at other Southern Hemisphere sites; with the lower concentrations comparable with those in present-day Antarctic snow. Trace metal concentrations spanned two orders of magnitude, and were not obviously related to air-mass trajectories. The seawater contribution to rainwater trace metals was negligible. Cd, Cu, Pb, and Zn were enriched in rainwater relative to crustal material, and a significant anthropogenic contribution to these elements is tentatively suggested. Limited Pb isotope data link anthropogenic Pb with high Pb enrichment. Cd, Pb, Zn, and H+ were correlated with each other, suggesting a common source. Fe and Mn were correlated, and had a predominantly crustal dust source. Cd and Pb were correlated with 210 Pb , implying that these metals were associated with submicrometre-sized aerosols.
Keywords: Rainwater; Anthropogenic; Lead-210; Metal speciation; Sea salt;

Aerosol vanadium at McMurdo Station, Antarctica: by Douglas H Lowenthal; Judith C Chow; David M Mazzera; John G Watson; Byard W. Mosher (677-679).
Measurements at McMurdo Station, Antarctica demonstrate that the combustion of light-weight fuel oil (AN-8) at the station is not a significant source of vanadium in ambient aerosols there. It is concluded by inference that the elevated levels of vanadium found previously at Dye 3, Greenland, where diesel fuel arctic (DFA) was used for power generation and surface vehicles, were due to aerosol transport from North America, not contamination from local sources.
Keywords: Long-range transport; Vanadium; Dye 3; McMurdo; Enrichment factor;