David Yap

Ten-year trends in sulphate, nitrate and hydrogen deposition in central Ontario

Abstract The decrease in emissions of SO2 in eastern North America in the past decade was strongly correlated with a decrease in bulk deposition rates and concentrations of SO42− and H+ in precipitation in central Ontario. Nitrate emissions, deposition and concentration have not changed significantly over the same period.

A synoptic climatology for surface ozone concentrations in Southern Ontario, 1976–1981

Abstract The synoptic climatology of ozone (O3) for S Ontario has shown that, over the 1976–1981 period, average summer O3 concentrations follow a relationship similar to that reported for event analysis during periods of high O3 concentration. Highest average concentrations, 36 parts per billion (ppb), occur with ‘back of the high’ situations while lowest average concentrations (20 ppb) occur with ‘front of the high’ situations. With similar weather events in the winter, the pattern is reversed with highest average O3 concentrations on the ‘front of the high’ (19 ppb) and lowest average concentrations on the ‘back of the high’ (13 ppb). Concentration of O3 in the ‘front of the high’ sector is due in part to the intrusion of O3 in the vicinity of storms from the stratosphere. The seasonal variation of average concentrations in these situations is low, ranging from 14 to 26 ppb. The very low average concentration during the winter and fall for the ‘back of the high’ situation may be the result of scavenging by NOx from the urban/industrial areas around the Great Lakes. During the spring and summer, solar energy and warm temperatures cause the photochemical production of O3 from NOx and HC s precursors. In the fall and winter, photochemical production of O3 is either very low or absent, and the NOx consume O3 rather than produce it. Thus, average O3 concentrations for winter ‘back of the high’ situations are one-third of those in the summer months. The synoptic climatology of events during the months from May to September with maximum O3 concentrations in excess of 80 ppb indicates that 78 % of these events occur under synoptic weather classes generally indicative of back or centre of the high situations.

Mercury deposition and sources for the upper great lakes region

Mercury concentrations and depositions for northeastern Minnesota were measured in precipitation to investigate depositional trends, relationships with major cations and anions, and possible source emission regions. Results for 1987–1990 showed that environmentally significant amounts of Hg are present in precipitation and air and are subsequently deposited to remote lake watersheds. Volume-weighted concentrations of total Hg in precipitation averaged about 18 ng Hg L−1 with calculated annual depositions near 15 μg Hg m−2. Mercury concentrations in precipitation are positively correlated with the major ions, conductivity, and pH, and are negatively correlated with precipitation volume. The best predictor equation from stepwise regression has an r2 of 0.65 with Mg and chloride concentrations as predictor variables. From measurements of Hg in rain concentrations as a function of time within events, scavenging ratios for “washable” Hg were calculated to be 140 ± 80 (mass based at a 1 mm hr −1 precipitation rate). Up to about 10% of the total Hg in air is subject to washout by precipitation for a given event. Air parcel back-trajectories indicate that possible source regions within 72-hr travel time were located mostly to the south, southeast, and southwest, up to 2500 km distance away but local sources may also be important.

An assessment of source contributions to the ozone concentrations in southern Ontario, 1979–1985

Abstract Source contributions to the surface O3 concentrations in southern Ontario were assessed for the 1979–1985 period. Ozone episode analyses indicate a frequency of about nine episodes per year (15 episode-days). These occur primarily in the summer months and are generally manifestations of the northern extent of the O3 problem in eastern North America. Widespread elevated O3 levels tend to occur under weather classes indicative of back or centre of the high pressure situations and associated flow/trajectory from areas south/southwest of the lower Great Lakes. These episodes vary considerably from year-to-year. Local impacts on O3 levels are generally small. A study of O3 levels during cloud-free summer days for the period 1981–1985 gave local ‘background’ O3 levels of about 20–30 ppb daily and 30–50 ppb hourly maxima. The O3 contributions from the U.S. to southern Canada (assuming local ‘background’ O3 levels to be independent of wind direction) were estimated to be 30–35 ppb daily and 30–50 ppb hourly maxima. These results indicate an overall O3 contribution of about 50–60% from the U.S. to southern Ontario. For episode-days, the U.S. contribution is even more significant.

Urban air pollution and atmospheric diffusion research in China

Air pollution has become a serious problem in China as a result of that countrys efforts in the last 30 years to become a great industrial power. The burning of coal, which currently provides over 70% of all Chinas energy needs, is a major source of air pollution. Because Chinese coal is high in sulfur and ash content and because most combustion devices in China have low efficiencies, SO2 and particulate emissions are a serious problem and are comparable to or exceed those found in many countries that are much more industrialized. Although most coal is burned in North China, acid precipitation is most severe in South China because of the lack of buffering loess dust found in the former region.The Chinese government has already taken major steps to mitigate air pollution, such as relocating polluting industries, supplying coal with lower sulfur content, using gas instead of coal for residential heating, and levying fines on industries that exceed pollution standards. Atmospheric environmental impact assessment (AEIA) is also required for all major new projects. This article describes three types of mathematical diffusion models and field and wind-tunnel experiments that are used in such assessments.The Chinese authorities believe that a range of technological, managerial, locational, and behavioral changes must be effected before the air of Chinese cities can be significantly improved.

An analysis of the impact of the sudbury smelters on wet and dry deposition in Ontario

Abstract Meteorological analyses of acidic deposition data were undertaken to quantify the effect of Sudbury emissions on precipitation quality and air quality in Ontario during the period 1980–1983 with particular emphasis on the Sudbury smelter shutdown period (July 1982–March 1983). The techniques used included air parcel trajectories and detailed meteorological analysis. Results indicate that the contribution of the Sudbury smelters to sulphate wet deposition in central and southern Ontario was small—less than 12 % of the wet deposition at the study sites. The smelter contribution to sulphur dry deposition was greater—possibly as high as 47 % of the total at Kapuskasing, and up to about 20–30% of the total in central Ontario, with a smaller contribution (less than 5 %) to the southwest and west of Sudbury. These percentages apply to the smelter emission rate in the early 1980s, i.e. about 0.9 million metric tons of SO2 per year.

Climatology of convective boundary-layer parameters over Ontario, Canada

The climatology of convective boundary layer (CBL) parameters over Ontario, Canada was examined for a 5-year summer period 1981–1985. The following variables, important for dispersion of pollutants in the daytime CBL, were determined from routine meteorological observations, namely: the mixed layer height (zi), the surface heat flux (Ho), the convective velocity scale (w∗) and atmospheric stability parameters (uw∗ and (1L where ū is the mean horizontal wind speed in the CBL and L is the Monin-Obukov length). For the summer months in Ontario, results indicate small decreases in the maxima of zi, Ho and w∗ from south to north. Typically, zirn is in the range 1200–1500 m, Hom between 150 and 180 Wm−2 and w∗m between 1.7 and 1.9ms−1. The stability parameter uw∗ ranges from 4.0 to 4.6, and the frequency of summer convective days in Ontario is about 80% (based on uw∗0⩽ 6.0 or 1L ⩽ −0.005 m−1). On a diurnal basis, Ho peaks near noon, w∗ about 1 h later and zi an additional 2 h later. For Ontario as a whole, w∗m for the summer months can be estimated from the following simple linear expression: w∗m = 0.75 + 7.9 × 10−4zim (r2 = 0.84) where zim is expressed in m and w∗m in ms−1.

Modelling sulphur dioxide levels in the Sarnia area

For environmental planning and policy-making purposes, this study was undertaken to apply the Ontario Ministry of the Environment Air Quality Model for SO2 to an urban-industrial region, namely, the Sarnia and St. Clair River area. Predicted and measured SO2 levels showed good agreement. A comparison of daily model predictions with 118 observations from 11 monitoring stations for 12 days in 1973 gave an overall correlation coefficient of 0.88.