Walter H. Chan

Acid rain in southwestern China

Abstract Acid rain and acidification of the environment have been environmental issues of concern in China in recent years. Approximately 90% of the monitoring stations with a mean pH of less than 5.6 are located south of the Yangtze River. In this account, new research data have been combined with those published originally in Chinese to give an overview of the acid rain picture in SW China, a region with the most serious acid rain problem in China. Results of SW China have been presented in comparison with data in northern parts of China to not only demonstrate the spatial variability, but also to reflect the impact of NH 3 , airborne particles and soil types on rain acidity. Based on precipitation and aerosol chemistry measurements, the source and origin of acid rain in SW China are discussed.

On the concentration of trace metals in precipitation

Abstract Recent precipitation chemistry data of known reliability indicate that typical rural concentrations of Cd, Cu, Pb, Ni, V and Zn are lower than those indicated by older measurements owing to sample contamination. Furthermore the concept of ‘typical remote concentrations’ may not be appropriate unless it is qualified by the distance from sources and the prevailing meteorological air masses.

Concentration and deposition of trace metals in Ontario-1982

Results of trace metal concentrations in air and precipitation and the corresponding wet and dry deposition in Ontario in 1982 arc reported. In terms of the spatial patterns, in general, there was a decreasing gradient from south-to-north in both concentration and deposition. Patterns differed with each parameter although certain groups of metals (e.g., Fe and Al; Pb, Zn, and Mn) displayed similar patterns. In general, wet deposition was greater than dry deposition at all sites. Geographically, the variability in the wet to dry deposition ratio for coarse particles (MMD > 2.5 μm) was small. However, it increased from the south to the north for fine particles (MMD < 2.5 μm), being higher away from the source areas. Scavenging ratios (W) have been derived from the precipitation and air concentrations of trace metals. The scatter in W is quite large for all trace metals, up to 2 orders of magnitude. There was little seasonal variability in W for fine particles (Pb, Mn, Zn, and Cd). However, coarse particles (Fe, Al, and Cu) were more efficiently scavenged by snow than by rain.

Impact of INCO smelter emissions on wet and dry deposition in the Sudbury area

Abstract The results presented here are based on approximately 2 years (mid-1978 to mid-1980) of ambient air and precipitation concentration monitoring of selected pollutants, including S compounds and trace metals, in the Sudbury area. Together with supporting measurements of particle size distributions, the air concentration data were used to estimate dry deposition rates. A detailed meteorological analysis of the data allowed the smelter impact on the wet and dry deposition of S and trace metals to be determined. With the exception of Cu and Ni, most of the wet deposition in the Sudbury area (within a radius of 40 km) can be attributed to sources other than the INCO smelter. Nevertheless, a definite influence of the smelter on the local downwind precipitation quality can be detected for almost all the substances known to be emitted. For example, average downwind precipitation Cu and Ni concentrations were found to be an order of magnitude higher than background values. In many cases, the INCO smelter influence can be detected at distances of more than 40 km from the source. Most particulate constituents (acids, sulfates, trace metals) are scavenged quite efficiently from the smelter plume during both rain (and snow) storms, with almost total removal occurring within the Sudbury area ( R = 40 km) for some trace metals (e.g. copper). On the other hand, the percentage of total emitted S scavenged by precipitation locally is quite small, mainly because this S is largely in the form of SO 2 , which is subject to a low precipitation scavenging efficiency. During precipitation events, the INCO smelter contributes, on average, 70% of the total Cu and Ni wet deposition within 40 km of the smelter, and less than 20% of the total for other trace metals and S. Dry deposition is estimated to be a relatively inefficient removal mechanism for plume SO 2 and other substances present predominantly in the sub-μm particle size range (i.e. SO 4 2− , Pb, Zn, Cd), less than 20% of the emissions being deposited within 40 km of the smelter sources. On the other hand, it is estimated that a higher proportion of the particles in the coarse size range (containing most of the airborne Fe, Al and Ni) (up to about 15%) is deposited within this same distance. During the study period, the smelter contribution to the total dry deposition within 40 km was greatest for S (primarily due to SO 2 ) and nickel, making up 25 and 64% of the total. The contribution of the other metals examined (Fe, Pb, Zn, Cd and Al) was generally less than 20%. For S and trace metals in large particles (Fe, Ni, Al) wet and dry deposition is similar. Particles in the sub-μm size range (Zn, Pb, Cd) are primarily deposited by precipitation. As far as total deposition is concerned, the major smelter impact is on Cu and Ni. For most of the other substances examined, INCO contributes about 20% or less.

An evaluation of sorption properties of precipitation constituents on polyethylene surfaces

Experiments with both synthetic and actual precipitation samples at pH near 4 have been carried out to examine whether polyethylene surfaces are suitable for sampling inorganics in precipitation. For the parameters studied, it is found that contamination due to desorption is minimal. Of the major ions, there is no significant adsorption of H+, SO4−2, NO3−, NH4+, Cl−, Ca2+, Mg2+ and Na+; however, loss of K+ due to adsorption is observed. There is negligible adsorption on polyethylene of Fe, Cu, Ni, Pb, Cd and Cr on one day contact; however, loss of Zn and Al amounts to 20 %. It is found that adsorption of Ni, Pb and Mn is minimal over 29 days and that of Cd is about 10 %. Fe, Cu, Zn and Al have adsorption losses ranging from 26 % to 47 % over the same interval.

Regional-scale precipitation scavenging of SO2, SO4, NO3 and HNO3

Abstract Daily air and precipitation concentration data from monitoring sites in the APIOS network were examined to yield rain and snow scavenging ratios of SO2, SO42−, NO3t− and HNO3. Rain is more efficient in scavenging SO42− than it is for SO2. Snow is slightly more efficient than rain in scavenging SO42−. However, the scavenging of SO2 by snow is negligible. Both rain and snow are more efficient in scavenging HNO3 than NO3−. While the scavenging efficiencies of HNO3 by rain and snow are comparable, snow is more efficient than rain in scavenging NO3−. On an annual basis, scavenging ratios W derived from precipitation (mg l−1) and air (μg −3) concentrations, are estimated for SO42− to be 4.3 × 105; for SO2 to be 4.6 × 104; for NO3− to be 4.7 × 105 and for HNO3 to be 8.4 × 105. On average, direct scavenging of ambient air SO2 and NO3− accounts for less than 15 % of the SO42− and NO3− in precipitation.

Airborne particulate size distribution measurements in nickel smelter plumes

Abstract This paper reports the results of particle sizing measurements in the plume from two smelters at Sudbury, Ontario (INCO and Falconbridge) which were studied in 1979 and 1980. Andersen impactors, mounted on a Hughes 500C helicopter, were used. Due to bounce-off problems, it was found necessary to use sticky substrates for the coarse particles. In both the INCO and Falconbridge smelters, constituents could be classified as coarse particles having mass median diameter equal to or greater than 2.5 μm (including Fe, Cu, Ni, Al and Mn) and fine particles having mass median diameter less than 2.5 μm (including SO4Pb, Zn, Cd and As). Most of these distributions were not log-normal, but displayed bimodal or multi-modal characteristics.

Scavenging ratios of acidic pollutants and their use in long-range transport models

Abstract The scavenging ratios for SO 2 , SO 4 2− and NO 3 − vary markedly (over two orders of magnitude) between precipitation events, and are shown to possess log-normal distributions. Using a constant value of scavenging ratio as an input parameter into a model, as is the general practice, will lead to significant errors in model calculations. Scavenging ratios for SO 4 2− show little spatial variation. The spatial variability for NO 3 − is larger. Also, the scavenging ratios for NO 3 − suggest that in-cloud formation, NO 3 may be important.

Analysis of an acidic deposition episode at dorset, Ontario

Abstract This study is concerned with an acidic deposition episode which occurred at Dorset in the ecologically sensitive Muskoka-Haliburton area of Ontario during the period 28 August–4 September 1981 when 12 % of the total 1981 precipitation fell. The wet deposition of both the sulfate and free hydrogen ions during this 8-day period accounted for 28% of the total 1981 wet deposition. The wet deposition of nitrate accounted for 16% of the 1981 total wet deposition. A trajectory study implicates pollution sources south and southwest of the study region.

An evaluation of artifact SO42− formation on nylon filters under field conditions

Abstract The extent of SO2 conversion on Membrana (Ghia) Nylasorb nylon filters under field conditions has been evaluated and found to be quite variable. The S-SO42− loading on the nylon filters is higher at higher SO2 concentrations, and on a long term basis approaches a saturatio limit of 2.5 μg S-SO42− on a 47mm disc, at a dosage of 230 μg SO2 approximately. The % conversion decreases as the SO2 concentration increases. On a long term basis, at an SO2 concentration range of 1.0–7.7 μg m−3, the conversion ranges from 8.2% to 2.1%. The dependence of SO2 conversion on nylon filters on relative humidity displays a diurnal pattern. An expression has been derived to explain the observed % SO2 conversion on nylon filters as a combined effect of the ambient SO2 concentration and relative humidity.