Tom Dann

ASSOCIATION BETWEEN PARTICULATE- AND GAS-PHASE COMPONENTS OF URBAN AIR POLLUTION AND DAILY MORTALITY IN EIGHT CANADIAN CITIES

Although some consensus has emerged among the scientific and regulatory communities that the urban ambient atmospheric mix of combustion related pollutants is a determinant of population health, the relative toxicity of the chemical and physical components of this complex mixture remains unclear. Daily mortality rates and concurrent data on sizefractionated particulate mass and gaseous pollutants were obtained in eight of Canadas largest cities from 1986 to 1996 inclusive in order to examine the relative toxicity of the components of the mixture of ambient air pollutants to which Canadians are exposed. Positive and statistically significant associations were observed between daily variations in both gas- and particulate-phase pollution and daily fluctuations in mortality rates. The association between air pollution and mortality could not be explained by temporalvariation in either mortality rates or weather factors. Fine particulate mass (less than 2.5 μm in average aerometric diameter) was a stronger predictor of mortality than coarse mass (between 2.5 and 10 μm). Size-fractionated particulate mass explained 28% of the total health effect of the mixture, with the remaining effects accounted for by the gases. Forty-seven elemental concentrations were obtained for the fine and coarse fraction using nondestructive x-ray fluorescence techniques. Sulfate concentrations were obtained by ion chromatography. Sulfate ion, iron, nickel, and zinc from the fine fraction were most strongly associated with mortality. The total effect of these four components was greater than that for fine mass alone, suggesting that the characteristics of the complex chemical mixture in the fine fraction maybe a better predictor of mortality than mass alone. However,the variation in the effects of the constituents of the fine fraction between cities was greater than the variation in the mass effect, implying that there are additional toxic components of fine particulate matter not examined in this study whose concentrations and effects vary between locations. One of these components, carbon, represents half the mass of fine particulate matter. We recommend that measurements of elemental and organiccarbon be undertaken in Canadian urban environments to examine their potential effects on human health.

The Relationship Among TSP, PM10, PM2.5, and Inorganic Constituents of Atmospheric Participate Matter at Multiple Canadian Locations

Abstract The Canadian NAPS (National Air Pollution Surveillance) network has produced one of the largest and more geographically diverse databases of high quality atmospheric particle measurements in the world. A maximum of ten and a minimum of two years of data are available for 19 Canadian locations. These data were used to investigate relationships between collocated measurements of TSP, PM10, PM2.5, SO4 2-, and other inorganic ions and elements at a variety of urban and rural locations. Amongst all locations and all 24-hour measurements, the 10th and 90th percentile TSP concentrations were 22 and 98 μg m-3, respectively. A majority of the PM10 concentrations were below 47 μg m-3 and most of the PM2 5 concentrations across Canada were below 26 μg m-3 (90th percentiles). On average across all sites, PM25 accounted for 49% of the PM10, and PM10 accounted for 44% of the TSP. However, there was considerable variability among sites, with the mean PM2.5 to PM10 ratio ranging from 0.36 to 0.65. This ratio als...

Associations between short-term changes in nitrogen dioxide and mortality in Canadian cities.

The association between daily variations in ambient concentrations of nitrogen dioxide (NO2) and mortality was examined in 12 of Canadas largest cities, using a 19-yr time-series analysis (from 1981-1999). The authors employed parametric statistical methods that are not subject to the recently discovered convergence and error estimation problems of generalized additive models. An increase in the 3-d moving average of NO2 concentrations equivalent to the population-weighted study mean of 22.4 ppb was associated with a 2.25% (t = 4.45) increase in the daily nonaccidental mortality rate and was insensitive to adjustment for ozone, sulfur dioxide, carbon monoxide, coefficient of haze, size-fractionated particulate mass, and the sulfate ion measured on an every-6th-day sampling schedule. The 3-d moving average of NO2 was sensitive to adjustment for fine particulate matter measured daily during the 1998-2000 time period.

Ambient biogenic hydrocarbons and isoprene emissions from a mixed deciduous forest

Experiments were conducted during the growing season of 1993 at a mixed deciduous forest in southern Ontario, Canada to investigate the atmospheric abundance of hydrocarbons from phytogenic origins, and to measure emission rates from foliage of deciduous trees. The most abundant phytogenic chemical species found in the ambient air were isoprene and the monoterpenes α-pinene and β-pinene. Prior to leaf-bud break during spring, ambient hydrocarbon mixing ratios above the forest remained barely above instrument detection limit (∼20 parts per trillion), but they became abundant during the latter part of the growing season. Peak isoprene mixing ratios reached nearly 10 parts per billion (ppbv) during mid-growing season while maximum monoterpene mixing ratios were close to 2 ppbv. Both isoprene and monoterpene mixing ratios exhibited marked diurnal variations. Typical isoprene mixing ratios were highest during mid-afternoon and were lowest during nighttime. Peak isoprene mixing ratios coincided with maximum canopy temperature. The diurnal pattern of ambient isoprene mixing ratio was closely linked to the local emissions from foliage. Isoprene emission rates from foliage were measured by enclosing branches of trees inside environment-controlled cuvette systems and measuring the gas mixing ratio difference between cuvette inlet and outlet airstream. Isoprene emissions depended on tree species, foliage ontogeny, and environmental factors such as foliage temperature and intercepted photosynthetically active radiation (PAR). For instance, young (<1 month old) aspen leaves released approximately 80 times less isoprene than mature (>3 months old) leaves. During the latter part of the growing season the amount of carbon released back to the atmosphere as isoprene by big-tooth and trembling aspen leaves accounted for approximately 2% of the photosynthetically fixed carbon. Significant isoprene mixing ratio gradients existed between the forest crown and at twice canopy height above the ground. The gradient diffusion approach coupled with similarity theory was used to estimate canopy isoprene flux densities. These canopy fluxes compared favorably with values obtained from a multilayered canopy model that utilized locally measured plant microclimate, biomass distribution and leaf isoprene emission rate data. Modeled isoprene fluxes were approximately 30% higher compared to measured fluxes. Further comparisons between measured and modeled canopy biogenic hydrocarbon flux densities are required to assess uncertainties in modeling systems that provide inventories of biogenic hydrocarbons.

Further interpretation of the acute effect of nitrogen dioxide observed in Canadian time-series studies.

In this paper, the pooled NO2 association with nonaccidental mortality is examined across 10 cities in Canada in single- and two-pollutant time-series models. The results reaffirm that NO2 has the strongest association with mortality, particularly in the warm season. Although attributing such effects to NO2 cannot be ruled out, it is plausible that NO2 is acting as an indicator for some other exposure affecting the population. This could include PM2.5, as has been suggested from some personal exposure data, but it could also be indicating a more specific type of PM2.5, such as traffic-related particles, given that in cities the main source of NO2 is motor vehicle exhaust. NO2 could also be acting as a surrogate for other pollutant(s) originating from motor vehicles or high-temperature combustion, such as volatile organic compounds (VOCs) or polycyclic aromatic hydrocarbons. Another possibility is other oxidized nitrogen species (“NOz”) or photochemically produced pollutants that can co-vary with NO2, especially during urban stagnation events. Data to test these different possibilities across several Canadian cities are examined. The focus is on correlations in time or space between NO2 and other pollutants that are more strongly linked to vehicle emissions. The results support the hypothesis that NO2 is a better indicator than PM2.5 of a range of other toxic pollutants. This includes VOCs, aldehydes, NOz and particle-bound organics in motor vehicle exhaust. Thus, overall, the strong effect of NO2 in Canadian cities could be a result of it being the best indicator, among the pollutants monitored, of fresh combustion (likely motor vehicles) as well as photochemically processed urban air.

Temporal and spatial relationships in fine particle strong acidity, sulphate, PM1O, and PM2.5 across multiple canadian locations

The Canadian Acid Aerosol Measurement Program (CAAMP) was established in 1992 to gain a better understanding of the atmospheric behaviour of fine particle strong acidity (“acid aerosols”) and to facilitate an assessment of the potential health risks associated with acid aerosols and particles in general. During 1992. 1993 and 1994, annular denuder and filter measurements were taken at four sites in Ontario, two in Quebec, three in the Atlantic Provinces and one in the greater Vancouver area. Mean fine particle sulphate concentrations (SO42−) were highest in southern Ontario (annual average ranged from 40–70 nmol m−3), lowest at a site in the Vancouver area (average = 16 nmol m−3) and second lowest in rural Nova Scotia. However, mean fine particle strong acid concentrations (H+) were geographically different. The highest mean concentrations were at the east coast sites (annual average of up to 30 nmol m−3). Acidities were lower in areas where the fine particle acidity experienced greater neutralization from reaction with ammonia. This included the major urban centres (i.e. Toronto and Montreal) and areas with greater amounts of agricultural activity, as in rural southern Ontario. On average, ambient concentrations of fine and coarse particle mass were larger in the urban areas and also in areas where SO42− levels were higher. All the particle components were episodic. However, compared to SO42− and fine particles (PM2.5 or PM2.1, depending upon inlet design), episodes of H+ tended to be less frequent and of shorter duration, particularly in Ontario. Saint John, New Brunswick, had the highest mean annual H+ concentration, which was 30 nmol m−3. H+ episodes (24 h concentration > 100 nmol m−3) were also the most frequent at this location. The high levels in Saint John were partially due to local sulphur dioxide sources and heterogeneous chemistry occurring in fog, which, on average, led to a 50% enhancement in sulphate, relative to upwind conditions. There was a substantial amount of intersite correlation in the day to day variations in H+, SO42− , PM2.5 and PM10 (fine + coarse particles) concentrations, which is due to the influence of synoptic-scale meteorology and the relatively long atmospheric lifetime of fine particles. Sulphate was the most regionally homogenous species. Pearson correlation coefficients comparing SO42− between sites ranged from 0.6 to 0.9, depending on site separation and lag time. In many cases, particle episodes were observed to move across the entire eastern portion of Canada with about a two-day lag between the SO42− levels in southern Ontario and in southern Nova Scotia.

Receptor model based identification of PM2.5 sources in Canadian cities

Abstract Source apportionment of 24–hour integrated PM 2.5 chemical speciation data, collected at five Canadian urban sites, Windsor, Toronto, Montreal, Halifax, and Edmonton was performed using the receptor model, Positive Matrix Factorization (PMF). In order to determine the influences of local and regional sources, in–depth wind direction and back trajectory analyses were performed using the conditional probability function (CPF) and the potential source contribution function (PSCF). The highest PM 2.5 levels were observed in Windsor followed by Toronto and Montreal. Secondary sulfate and nitrate were the major factors contributing to the PM 2.5 mass, accounting for 41% – 61% in the five sites. These secondary factors were associated with trans–boundary emissions from Ohio, Pennsylvania, and New York. An elemental carbon (EC)–rich factor was identified in Windsor, Toronto, and Montreal, characterized by distinct EC and organic carbon (OC) profiles. The EC–rich factor accounted for 6% – 19% of the total PM 2.5 mass in summer and also appeared to be related to trans-boundary pollutants. The combined contributions of traffic and road dust ranged from 14% to 19%, with a portion of the nitrate factor also coming from vehicles. In Halifax, sea salt was the second strongest source, contributing 18% of the PM 2.5 . In Edmonton, strong correlation of volatile organic compounds with the major PM 2.5 factors suggested that local industrial sources were significant sources of secondary aerosol. Further, biomass burning contributed 12% of the PM 2.5 mass in Edmonton. Both local and regional sources were found to contribute at all sites. Thus, PM 2.5 can be reduced at all the sites through local controls. However given the significant contribution of trans–boundary contributions to the PM 2.5 mass, a substantial reduction of PM 2.5 in four of the cities will also require agreements to limit the production and transport of trans–boundary pollutants.

Ground-Level Ozone in Eastern Canada: Seasonal Variations, Trends, and Occurrences of High Concentrations

Over the past few years, concern has increased in Canada over the health and environmental impacts of elevated concentrations of ground-level ozone. During the summer the most populated regions of Canada frequently record ozone concentrations that exceed the one-hour average maximum acceptable air quality objective of 32 parts per billion (ppb). In 1988 the Canadian Council of Ministers of the Environment agreed to develop a federal/provincial management plan to control nitrogen oxide and volatile organic compound emissions to reduce ozone concentrations in all affected regions of the country. In addition to the proposed interim control measures, the plan recommended that studies be undertaken to acquire the information necessary to develop sound control strategies. This report represents one of those studies and provides a summary of ground-level ozone measurements for eastern Canada for the 1980 to 1991 period with an emphasis on seasonal variations, trends, and occurrences of high concentrations. South...

Modelled and field measurements of biogenic hydrocarbon emissions from a Canadian deciduous forest

Abstract The Biogenic Emission Inventory System (BEIS) used by the United States Environmental Protection Agency (Lamb et al., 1993, Atmospheric Environment 21, 1695–1705; Pierce and Waldruff, 1991, J. Air Waste Man. Ass. 41, 937–941) was tested for its ability to provide realistic microclimate descriptions within a deciduous forest in Canada. The microclimate description within plant canopies is required because isoprene emission rates from plants are strongly influenced by foliage temperature and photosynthetically active radiation impinging on leaves while monoterpene emissions depend primarily on leaf temperature. Model microclimate results combined with plant emission rates and local biomass distribution were used to derive isoprene and α-pinene emissions from the deciduous forest canopy. In addition, modelled isoprene emission estimates were compared to measured emission rates at the leaf level. The current model formulation provides realistic microclimatic conditions for the forest crown where modelled and measured air and foliage temperature are within 3°C. However, the model provides inadequate microclimate characterizations in the lower canopy where estimated and measured foliage temperatures differ by as much as 10°C. This poor agreement may be partly due to improper model characterization of relative humidity and ambient temperature within the canopy. These uncertainties in estimated foliage temperature can lead to underestimates of hydrocarbon emission estimates of two-fold. Moreover, the model overestimates hydrocarbon emissions during the early part of the growing season and underestimates emissions during the middle and latter part of the growing season. These emission uncertainties arise because of the assumed constant biomass distribution of the forest and constant hydrocarbon emission rates throughout the season. The BEIS model, which is presently used in Canada to estimate inventories of hydrocarbon emissions from vegetation, underestimates emission rates by at least two-fold compared to emissions derived from field measurements. The isoprene emission algorithm proposed by Guenther et al. (1993), applied at the leaf level, provides relatively good agreement compared to measurements. Field measurements indicate that isoprene emissions change with leaf ontogeny and differ amongst tree species. Emission rates defined as function of foliage development stage and plant species need to be introduced in the hydrocarbon emission algorithms. Extensive model evaluation and more hydrocarbon emission measurement;: from different plant species are required to fully assess the appropriateness of this emission calculation approach for Canadian forests.

OBSERVATIONS AND INTERPRETATIONS FROM THE CANADIAN FINE PARTICLE MONITORING PROGRAM

Canadian particle monitoring programs examining PM10, PM2.5, and particle composition have been in operation for over 10 years. Until recently, the measurements were manual/filter-based with 24-hr sample collection varying in frequency from daily to every sixth day, using GrasebyAnderson dichotomous samplers. In the past few years, these monitoring activities have been expanded to include hourly measurements using tapered element oscillating microbalances (TEOMs). This continuous monitoring program started operation focusing on PM10, but now emphasizes PM2.5 through the addition of more TEOMs and switching of the inlets of some of the existing units. The data from all of these measurement activities show that there are broad geographical differences and also local- to regional-scale spatial differences in mass and composition of PM2.5. Due to variations in sources, significantly different PM2.5 concentrations are not uncommon within the same city. Comparison of nearby urban and rural sites indicates that 30 and 40% of the PM2.5 is from local urban sources in Montreal and Toronto, respectively. Hourly PM2.5 measurements in Toronto suggest that vehicular emissions are an important contributor to urban PM2.5. There has been a decreasing trend in urban PM2.5, with annual average concentrations between the 1987-1990 and 1993-1995 periods decreasing by 11 to 39%, depending upon the site. The largest declines were in Montreal and Halifax, and the smallest decline was in Toronto. Comparison of 24-hr TEOM and manual dichotomous sampler PM2.5 measurements from a site in Toronto indicates that the TEOM results in lower concentrations. The magnitude of this difference is relatively small in the warmer months, averaging about 12%. During the colder months the difference averages about 23%, but can be as large as 50%.