Atmospheric Environment (v.35, #34)

Daily average levels of nitrogen dioxide (NO2) and the time-matched, relative humidity-corrected airborne respirable suspended particulate (RSP*) data from four air quality monitoring stations of the Environmental Protection Department (EPD) Network were subjected to analysis employing a linear multivariate model for visibility in Hong Kong. The respective NO2 and RSP* contributions to the extinction coefficient for Hong Kong Observatory, σ ext(HKO) are estimated to be between 6–31% (mean: 17%) and 58–68% (mean: 62.5%), with a remainder of 11–30% (mean: 21%). The latter includes a small contribution due to Rayleigh scatter. The observed σ ext agrees reasonably well with model prediction. During the July–October 1999 period, the particle scattering coefficient, σ sp was determined at City University (CityU) in Kowloon with the aid of an integrated nepthelometer employing 3, 1-h sampling periods. This daily average value of σ sp(CityU) is well correlated with the corresponding σ ext(HKO). It is provisionally estimated that the fractional contribution by particulate absorption to σ ext(HKO) is likely to be less than that by particulate scattering. A reasonable apportionment for σ ext(HKO) is ∼39% particulate scattering, 19–29% particulate absorption, 17% gaseous absorption, and an estimated mean Rayleigh scatter of ∼4.3%. The unaccounted 16% is due to a negative bias assigned to deficiencies in sampling and in the various assumptions made. Results of continuous, 8-h daytime nephelometric measurements of σ sp at the CityU, and the water-soluble ambient RSP constituents sampled in tandem at the same site during the February–April 2000 period suggest that SO4 *, NH4 * and K are apparently associated with light scattering at CityU. However, only the SO4 * at this sampling site is related to time-matched σ ext(HKO). Based on these and other results from a previous study, it is concluded that (i) σ ext(HKO) is proportional to σ sp, measured elsewhere in Hong Kong at distances between several to ∼10 km from the HKO headquarters and (ii) most of the fine SO4 aerosol in Hong Kong is apparently advected into the territory.
Keywords: Hong Kong region; Visibility degradation; Multivariate analysis; Fine sulphate advection; Scattering and extinction coefficients;

More than 10 Asian dust storms occurring in Spring 2000 were found to transport dust long distances, with some fallout reaching as far as Taiwan. An air quality data set from Taiwan clearly shows that long-range transport of yellow-sand results in air quality in Taiwan, which is categorized as “Unhealthy” or “Very Unhealthy”. Backward trajectory analysis indicates that, for air parcels that arrived over Taiwan on 28 April, two or three days are required for transport from source regions, such as Inner Mongolia, a territory that is becoming a desert as a result of over-use and destruction of vegetation cover by human occupants. Furthermore, a 3-D long-range transport model for yellow sand, with an advanced size-dependent deflation module and driven by the NCAR/Penn State Fifth-Generation Mesoscale Model (MM5), is used to identify the long-range transport of yellow sand to Taiwan in April. Comparisons between observations and model calculations indicate that the model is able to reproduce some key features of the long-range transport. Transport of yellow sand to Taiwan is found to occur most easily when dust storms occurring in north China are accompanied by a high-pressure system located over the west of Japan. The high concentrations of yellow sand transported over Taiwan are usually between 500 and 1500 m high, not at the surface.
Keywords: Yellow sand; Observations in Taiwan; Transport; Modeling; Air quality;

Soot particles and their impacts on the mass cycle in the Tibetan atmosphere by Daizhou Zhang; Yasunobu Iwasaka; Guangyu Shi (5883-5894).
Atmospheric aerosol particles in urban and mountain areas around Lhasa city (29.65°N, 91.13°E) in the Tibetan Plateau were collected in the summers of 1998 and 1999. The particles were analyzed with electron microscopes and an energy dispersive X-ray spectrometer. Individual particle morphology, elemental composition and mixture of sulfate and nitrate were investigated. In the urban area, soot particles emitted from vegetation burning were dominant. These particles were characterized by chain or aggregate morphologies, and an elemental composition of potassium and sulfur. Such particles were frequently detected in mountain areas out of the city, where they formed droplets acting as condensation nuclei. Quantitative estimation indicated that sulfur was accumulated onto the soot particles during their dispersion from the urban area to mountain areas. Sulfate and nitrate detections indicated that soot particles collected in the urban area did not contain nitrate and BaCl2-reactive sulfate, which revealed that the combination of sulfur and potassium in the particles was not K2SO4. In contrast, the particles dispersed to mountain areas contained BaCl2-reactive sulfate and some contained nitrate, suggesting that soot particles emitted from the urban area could increase the buffering capacity of aerosol particles and enhance the formation of particulate sulfate through heterogeneous conversion in the Tibetan atmosphere.
Keywords: Tibet; Vegetation burning; Soot; Transport;

Information of volatile organic compounds (VOCs) in buildings in Hong Kong is relatively scared compared to other countries. Information of how much VOC accumulation comes from occupants themselves, from building materials and other outdoor sources are scarce even on a global basis. This study aimed at collecting information of the levels of individual VOCs using US-EPA Method TO-14. Twenty building premises including offices and public places such as customer service centers, shopping centers, etc. were studied. Samples were taken during the time slots when the mechanical ventilation system was operating. The 43 VOCs were grouped into three categories, i.e. aromatic hydrocarbons, chlorinated hydrocarbons and organohalogen. The most dominant VOCs found in the indoor samples were benzene, toluene, ethylbenzene, xylenes (BETX), chloroform and trichloroethylene as 100% of the samples were found to contain these VOCs. Besides, more than 75% of the samples were found to contain 1,3,5-trimethylbenzene, methylchloride and dichloromethane. The wt% of chlorinated hydrocarbons (48%) and the wt% of aromatic hydrocarbons (38%) only differed by about 10% in the office sector. Organohalogen (14%) contributed to the smallest fraction of the total on all the premises in the office sector on weight basis. A completely different distribution pattern was found in the non-office sector. The most abundant class of VOCs in terms of weight was aromatic hydrocarbons (80%). The second abundant class of VOCs was chlorinated hydrocarbons (14%) and was much less than the level of aromatic hydrocarbons in terms of weight. Organohalogen (6%) contributed to the smallest fraction of the total on all the premises in the non-office sector on weight basis.
Keywords: Volatile organic compounds; Ventilation; Office sector; Non-office sector; Hong Kong;

Estimate of total CO2 output from desertified sandy land in China by Duan Zhenghu; Xiao Honglang; Dong Zhibao; He Xingdong; Wang Gang (5915-5921).
Soil is an important factor in regional and global carbon budgets because it serves as a reservoir of large amount of organic carbon. In our study, using remote sensing data of different periods we analyzed the development and reversion of desertification in China, calculated the variations of organic carbon contents of the desertified lands in China. The results showed that the total storage of organic carbon in 0–50 cm soil layer of the desertified lands is 855 Mt. In recent 40 yr, the total CO2 amount released by land desertification processes to the atmosphere was 150 Mt, while the CO2 amount sequestered by desertification reversing processes corresponded to 59 Mt C. Hence, the net CO2 amount released from desertified lands of China corresponded to 91 Mt C, about 68.42% of the 133 Mt C of annual CO2 release in the global temperate and frigid zones. Simultaneously, it indicated that CO2 amount sequestered by desertification reversing processes in desertified land had greater potential than the other soils.
Keywords: Atmospheric environment; CO2; Desertification; Global change;

In April 2000 atmospheric trace gas measurements were performed on the western Indian Ocean on a cruise of the Dutch research vessel Pelagia from the Seychelles (5°S, 55°E) to Djibouti (12°N, 43°E). The measurements included analysis of dimethyl sulfide (DMS), acetone and acetonitrile every 40 s using PTR-MS (proton-transfer-reaction mass spectrometry) and gas chromatographic analyses of C2–C7 hydrocarbons in air samples taken during the cruise. The measurements took place at the end of the winter monsoon season and the sampled air masses came predominantly from the Southern Hemisphere, resulting in low concentrations of some long-lived hydrocarbons, halocarbons, acetone (350 pptv) and acetonitrile (120 pptv). On three consecutive days a diurnal cycle in DMS concentration was observed, which was used to estimate the emission of DMS (1.5±0.7×1013  molecules m−2  s−1) and the 24 h averaged concentration of hydroxyl (OH) radicals (1.4±0.7×106  molecules cm−3). A strongly increased DMS concentration was found at a location where upwelling of deeper ocean waters took place, coinciding with a marked decrease in acetone and acetonitrile. In the northwestern Indian Ocean a slight increase of some trace gases was noticed showing a small influence of pollution from Asia and from northeast Africa as indicated with back trajectory calculations. The air masses from Asia had elevated acetonitrile concentrations showing some influence of biomass burning as was also found during the 1999 Indian Ocean Experiment, whereas the air masses from northeast Africa seemed to have other sources of pollution.
Keywords: VOCs; NMHCs; Tropical marine boundary layer; DMS emissions; Variability–lifetime relationship; OH concentration;

Regional modelling of anthropogenic sulphur in Southeast Asia by M. Engardt; C.P. Leong (5935-5947).
A co-operative research project between the Malaysian Meteorological Service (MMS) and the Swedish Meteorological and Hydrological Institute (SMHI) focussing on the usage of an atmospheric transport and chemistry model, has just been initiated. Here, we describe the main features of the dispersion model and discuss a first set of calculations in light of available measurements of sulphuric species in Southeast Asia. According to our results, anthropogenic sulphur concentrations and depositions are particularly high near the large cities of the region, around a metal smelter in the southern Philippines, and in a region extending from northern Vietnam into southeastern China. These areas coincide with the high-emissions regions of Southeast Asia and we tentatively conclude that regional transport of acidifying species is not as far-reaching as in the mid-latitudes. From our calculations, and from supporting measurements we conclude that most of rural Southeast Asia is not yet severely affected by anthropogenic sulphur, but given the rapid rate of economical development in this region the situation may deteriorate quickly. Areas that are particularly at risk include the large cities, northern Vietnam, most of central Thailand, most of peninsular Malaysia, eastern Sumatra and parts of Java, all of which receive total-sulphur depositions in excess of 0.5 g S m−2  yr−1. Our model simulates sulphate in precipitation in accordance with measurements, but it has a tendency to overestimate atmospheric SO2. It remains to be investigated whether this is a problem in the model formulation or a result of unrepresentative sampling. An immediate continuation of this study should be performed with higher spatial resolution than the currently used 100×100 km2. Other imperfections in this model study, which should be addressed in future work, include parameterised vertical transport in deep convective clouds, the influence of natural emissions (primarily from volcanoes) on the concentration and deposition of sulphuric species, and the year-to-year variability of the driving meteorological conditions.
Keywords: MATCH; Air pollution; Malaysia; Thailand; Indonesia;

Polycyclic aromatic hydrocarbons (PAHs) and carbonyl compounds in urban atmosphere of Hong Kong by S.C Lee; K.F Ho; L.Y Chan; Barbara Zielinska; Judith C Chow (5949-5960).
Polycyclic aromatic hydrocarbons (PAHs) and carbonyls compounds are becoming a major component of atmospheric toxic air pollutants (TAPs) in Hong Kong. Many studies in Hong Kong show that traffic emission is one of the most significant contributors in urban area of Hong Kong. A twelve months monitoring program for PAHs and carbonyl compounds started on 10 April 1999 including a two weeks intensive sampling in winter had been performed at a roadside urban station at Hong Kong Polytechnic University in order to determine the monthly and seasonal variations of PAHs and carbonyl concentrations. The objective of this study is to characterize the roadside concentrations of selected TAPs (PAHs and carbonyl compounds) and to compare with the long-term compliance monitoring data acquired by Hong Kong Environmental Protection Department (EPD). Monthly variations, seasonal variations and winter/summer ratios at the monitoring station are discussed.
Keywords: PAHs; Carbonyls compounds; Seasonal variation; Road-side; Hong Kong;

Trends of ambient carbonyl compounds in the urban environment of Hong Kong by Della W.M Sin; Yiu-Chung Wong; Peter K.K Louie (5961-5969).
The concentrations of C1–C8 carbonyl compounds were measured at two urban sites in Hong Kong from October 1997 to September 2000. The daily total carbonyl concentrations were found to range from 2.4 to 37 μg m−3. Formaldehyde was the most abundant species, which comprised from 36 to 43% of the total detected carbonyls, followed by acetaldehyde (18–21%) and acetone (8–20%). The highest 24-hour average concentrations measured were 10 and 7.7 μg m−3 for formaldehyde and acetaldehyde, respectively. Seasonal and temporal variations in the concentrations of formaldehyde and acetaldehyde were not obvious, but lowest concentrations often occurred from June to August. The mean formaldehyde/acetaldehyde molar ratios at the two sites in summer (2.8±1.1 and 2.5±1.2) were significantly higher (p⩽0.01) than those in winter periods (1.9±0.6 and 2.0±0.6). The phenomena were explained by influences of both photochemical reactions and local meteorological conditions. Better correlations between formaldehyde and acetaldehyde, and between NO x and each of the two major carbonyls were obtained in winter periods indicating direct vehicular emissions were the principal sources. The ambient formaldehyde and acetaldehyde concentrations in the urban atmosphere of Hong Kong were within the normal ranges reported in the literature for other urban sites world-wide.
Keywords: Carbonyls; Trends; Urban air; Hong Kong;

Ambient air quality of two metropolitan cities of Pakistan and its health implications by Pravin P Parekh; Haider A Khwaja; Adil R Khan; Ronaq R Naqvi; Abdul Malik; Sajjad A Shah; Khalid Khan; Ghazanfar Hussain (5971-5978).
The present study reports findings on TSP loading in the ambient air of two major cities in Pakistan – Karachi and Islamabad. Data for TSP were collected at one site in Karachi and two in Islamabad between 10 December 1998 and 08 January 1999. This article reports one of the highest TSP loadings recorded so far in any megacity of the world. During the study period, average daily TSP concentrations at the Karachi site ranged from 627 to 938 μg m−3 with a mean of 668 μg m−3. On four occasions TSP concentrations were >1000 μg m−3 (range 1031–1736 μg m−3). At the Islamabad sampling site in close proximity to the city's industrial sector, daily TSP concentrations varied in the range of 428–998 μg m−3 (mean 691 μg m−3). Even at a relatively remote site of the city (Saidpur), TSP loading was high (range 145–448 μg m−3; mean 275 μg m−3). By virtue of the WHO definition, the 24-h average TSP concentrations in a busy commercial site in Karachi and in the vicinity of an industrial sector in Islamabad were in “exceedance” by a factor of 4–8. At Saidpur, the remote site, the 24-h average TSP loading exceeded the WHO guideline of 120 μg m−3 by a factor of 1.2–3.7.
Keywords: TSP; Atmospheric aerosols; Asia; Urban pollution;

Simultaneous measurements of ammonia and nitric acid in ambient air at Agra (27°10′N and 78°05′E) (India) by R.S Parmar; G.S Satsangi; A Lakhani; S.S Srivastava; S Prakash (5979-5988).
Simultaneous measurements of ammonia and nitric acid in ambient air were conducted at Dayalbagh, Agra using the mist chamber technique. The sampling site is located near a cattle shed. A total of 120 samples were collected during the period July–September and November–February (1997–1998). Sampling was performed during six different times a day. Gas-phase HNO3 was estimated as NO3 using ion chromatographic technique while ammonia was determined colorimetrically as NH4 + using indophenol blue method. The mean levels of NH3 and HNO3 for the entire data set were 16.3±2.8 and 1.6±1.4 ppbv, respectively. In the monsoon, mean values for NH3 and HNO3 averaged to 16.4±3.5 and 0.9±0.7 ppbv while the winter means were 11.8±4.4 and 2.1±1.2 ppbv, respectively. Concentration of both the species (NH3 and HNO3) did not show any significant diurnal behaviour in both the seasons. However, concentration of both NH3 and HNO3 were lower at dawn than the previous night's value. This has been ascribed to their removal through dew. Concentrations of HNO3 are observed to increase during the daytime, consistent with its formation by photochemical reactions. Nitric acid and ammonia concentrations show a significant seasonal variation. Levels of HNO3 are higher in winter but lower in monsoon, while ammonia shows a reverse trend with higher monsoon and lower winter values. Observed trends in nitric acid and ammonia concentration are due to seasonal variation in emission sources, chemistry and meteorology. Gaseous ammonia and nitric acid are in equilibrium with NH4NO3 (solid or aqueous) in the atmosphere. The existence of this equilibrium was examined from simultaneous measurements of NH3 and HNO3 in the ambient air. It is found that for the monsoon data, measured concentrations are qualitatively below the predicted equilibrium value, while in the winter, concentration product ([NH3] [HNO3]) lies consistently above the predicted values. These deviations may be explained due to local sources of both [NH3] and [HNO3], presence of coarse nitrate particles and low-temperature and high-humidity conditions.
Keywords: Ammonia; Nitric acid; Diurnal variation; Seasonal variation; Ammonium nitrate equilibrium;

Ionic composition of precipitation at the Central Anatolia (Turkey) by Burcu Tuncer; Banu Bayar; Canan Yeşilyurt; Gurdal Tuncel (5989-6002).
Concentrations of major ions, SO4 2−, NO3 , Cl, H+, Ca2+, K+, Mg2+, Ca2+ and conductivity were measured in approximately 300 daily, wet-only rain samples collected at a permanent rural station between 1993 and 1998. Concentrations of anthropogenic ions NH4 +, SO4 2− and NO3 were among the highest values reported in whole EMEP network, suggesting that the Anatolian plateau is under strong influence of distant emission sources. Although transport of pollutants have significant influence on the chemical composition of precipitation, average pH of the rainwater is 6.2 due to extensive neutralization of acidity. Approximately 95% of the acidity in collected samples is neutralized, particularly in summer season. The neutralizing agents are primarily CaCO3 and NH3. Concentrations of crustal ions are higher in summer season due to enhanced resuspension of soil particles from dry surface soil. Concentrations of anthropogenic ions SO4 2− and NO3 do not change significantly between summer and winter due to higher intensity of rains in summer season. Although concentrations of ions measured in this study is among the highest reported in EMEP network, wet deposition fluxes are low compared to flux values reported for similar sites in Europe, due to low annual precipitation in the Anatolia. Wet deposition fluxes of all measured parameters are highly episodic. Source regions affecting chemical composition precipitation in the Central Anatolia is investigated using trajectory statistics.
Keywords: Anatolia; Precipitation; Major ions; Deposition flux; Trajectory statistics;

Chemical characteristics of organic aerosols in Algiers city area: influence of a fat manufacture plant by Noureddine Yassaa; Brahim Youcef Meklati; Angelo Cecinato (6003-6013).
Total concentrations and homologue distributions of organic fraction constituents have been determined in particulate matter emitted from different units of a fat manufacturer (i.e. oils refining and conditioning plants, and production and conditioning units of a soap industry) located in Algiers area, as well as in atmospheric aerosols. In particular n-alkanes, n-alkanoic and n-alkenoic acids, n-alkan-2-ones and polycyclic aromatic hydrocarbons (PAH) were investigated. Organic aerosol contents varied broadly among the plant units, depending upon nature of the manufactured products. The percent composition of all classes of compounds investigated in ambient atmosphere was similar to those observed indoor at industrial plant units. Organic acids, n-alkanoic as well as n-alkenoic, appeared by far the most abundant organic constituents of aerosols, both indoor and outdoor, ranging from 7.7 to 19.8 and from 12.7 to 17.1 μg m−3, respectively. The huge occurrence of acids and n-alkanes in ambient aerosols was consistent with their high levels present in oil and fat materials. Among minor components of aerosols, n-alkan-2-ones and PAH, seemed to be related to thermally induced ageing and direct combustion of raw organic material used for oil and soap production.
Keywords: Particulate organic matter (POM); n-Alkanes; Monocarboxylic n-alkanoic acids; Monocarboxylic n-alkenoic acids; n-Alkan-2-ones; Polynuclear aromatic hydrocarbons (PAH); Air pollution; Vegetable oil and fat factory;

Eight trace elements, Si, Cl, K, Ca, Ti, Mn, Fe and Zn in the near-ground atmospheric aerosols were evaluated in the northwestern part of Mount Kenya using a dichotomous sampler and an EDXRF spectrometer. The samples were taken at 2 sites situated in Nanyuki area, which is roughly on the Equator. The sampler segregated the aerosol into two aerodynamic diameter (ad) size fractions, fine (<3.5 μm ad) and coarse (>3.5 and <18 μm ad). The elemental concentrations in the two size fractions were quantified and the elements assigned to known sources. Local wind blown dust related to agricultural activities and fire burning was found to dominate the lower tropospheric aerosols. There was inconclusive evidence of long range-transported aerosols being moved by night transport from the middle to the lower parts of the troposphere. Influence of the Indian Ocean marine aerosol was suggested but conclusive evidence was lacking.
Keywords: Dichotomous sampler; Atmospheric aerosols; EDXRF; Long range-transport; Biomass burning;

Chichi-jima island is located in the Pacific about 1000 km from the Japanese main island and is an ideal remote observatory from which to assess the long-range transport of polluted air from East Asia. The ozone concentration was measured from August 1997 to August 1998. Owing to the air mass change, the seasonal variation of ozone shows a distinct character: low concentration (about 13 ppbv) for the maritime air mass during the summer, and high concentration (about 40 ppbv) for the continental air mass during the winter. To assess the contribution of the long-range transport of polluted air during winter, nonmethane hydrocarbons were also measured in December 1999. Using backward trajectory analysis, the transport time of the air mass from the source area in the Pacific rim region was calculated for each sample. The concentration of hydrocarbons shows a clear negative correlation against the transport time. This analysis clearly shows the transport of polluted air, emitted in East Asia, to the Pacific during the winter. The plots of suitable hydrocarbon pairs showed that the decrease of hydrocarbon concentrations during winter is mainly caused by the mixing with clean background air.
Keywords: Nonmethane hydrocarbon; Ozone; East Asia; Long-range transport; Backward trajectory;

The results of one year's measurements (typically a two week sampling campaign in each season) of the concentrations of eight major water soluble ions, namely Na+, NH4 +, K+, Mg2+, Ca2+, Cl, NO3 and SO4 2−, in atmospheric aerosols collected in three New Zealand cities (Auckland, Christchurch and Hamilton) are presented. The data has provided important information on particulate soluble ion profiles in New Zealand urban areas and revealed some useful trends.A significant correlation has been found between the average meteorological conditions in a sampling campaign and the average particulate concentrations of some of these soluble ions in the campaign. For example, average particulate NO3 concentration in a campaign was found to correlate well with the average calm or weak wind duration percentage in the campaign, and the average concentrations of Na+, Mg2+ and Cl related closely to the average wind pattern and rainfall in the campaign.Significant site and seasonal variations have been observed with Hamilton having the lowest overall concentrations of all the soluble ions in the particles sampled. On average all sites had the highest particulate concentrations of Na+, Mg2+ and Cl in the summer but the highest particulate concentrations of NH4 + and non-sea-salt Ca2+ (nss-Ca2+) in the winter. The possible sources of PM10 mass have been deduced and in particular the relative contribution of sea salts to PM10 mass in the cities are reported.
Keywords: Meteorological effect; PM10; Site difference; Source apportionment; Sea salts;

Iron speciation and hydrogen peroxide concentrations in New Zealand rainwater by Robert J Kieber; Barrie Peake; Joan D Willey; Bethany Jacobs (6041-6048).
Rain was collected on the southern portion of the South Island of New Zealand during the summer of 1999 (January–March) during which time significant losses of ozone and increased UV were reported in the stratosphere over New Zealand. Iron and hydrogen peroxide concentrations were measured in rainwater because these analytes are directly influenced by photochemical processes and therefore are particularly susceptible to increasing UV levels. The absolute concentration of dissolved Fe(II) in New Zealand samples was very similar to summertime rain received in Wilmington, NC however the relative contribution of Fe(II) to total Fe was approximately twice as great in New Zealand samples. The larger percentage of reduced iron may reflect higher UV levels in New Zealand since Fe(II) is generated via photochemical reduction of particulate or dissolved Fe(III). No dissolved Fe(III) was detected in New Zealand rainwater, in contrast to the Wilmington site, where summertime Fe(III) concentrations are approximately equal to Fe(II) concentrations. Summertime hydrogen peroxide concentrations and diel variability in New Zealand were similar to other coastal and marine values in both the northern and southern hemispheres suggesting the increasing UV in New Zealand is not significantly increasing hydrogen peroxide concentrations at this location. Any excess photochemically produced hydrogen peroxide in New Zealand may be consumed through oxidation of Fe(II) which is rapidly reformed from photochemical reduction of Fe(III) by the higher UV levels in New Zealand.
Keywords: Hydrogen peroxide; Iron; Rainwater; New Zealand;