Julie Wallace

Topographic and spatial impacts of temperature inversions on air quality using mobile air pollution surveys

We investigated the spatial and topographic effects of temperature inversions on air quality in the industrial city of Hamilton, located at the western tip of Lake Ontario, Canada. The city is divided by a 90-m high topographic scarp, the Niagara Escarpment, and dissected by valleys which open towards Lake Ontario. Temperature inversions occur frequently in the cooler seasons, exacerbating the impact of emissions from industry and traffic. This study used pollution data gathered from mobile monitoring surveys conducted over a 3-year period, to investigate whether the effects of the inversions varied across the city. Temperature inversions were identified with vertical temperature data from a meteorological tower located within the study area. We divided the study area into an upper and lower zone separated by the Escarpment and further into six zones, based on location with respect to the Escarpment and industrial and residential areas, to explore variations across the city. The results identified clear differences in the responses of nitrogen dioxide (NO(2)) and fine particulate matter (PM2.5) to temperature inversions, based on the topographic and spatial criteria. We found that pollution levels increased as the inversion strengthened, in the lower city. However, the results also suggested that temperature inversions identified in the lower city were not necessarily experienced in the upper city with the same intensity. Further, pollution levels in the upper city appeared to decrease as the inversion deepened in the lower city, probably because of an associated change in prevailing wind direction and lower wind speeds, leading to decreased long-range transport of pollutants.

The effect of temperature inversions on ground-level nitrogen dioxide (NO2) and fine particulate matter (PM2.5) using temperature profiles from the Atmospheric Infrared Sounder (AIRS)

We investigate the effects of temperature inversions on the levels of nitrogen dioxide (NO2) and fine particulate matter (PM2.5) in the atmosphere over the Hamilton Census Metropolitan Area and environs in Ontario, Canada, for the period 2003 to 2007. Vertical temperature profiles extracted from data acquired by the Atmospheric Infrared Sounder (AIRS) were used to determine the occurrences of daytime and nighttime temperature inversions over the region. NO2 and PM2.5 data were obtained from three in situ air quality monitoring stations located in the study area. The results indicate increases of 49% and 54% in NO2 and PM2.5 respectively, during nighttime inversion episodes. Daytime inversions resulted in an 11% increase in NO2 but a 14% decrease in PM2.5. Decreases occurred predominantly in the summer. We discuss these results and possible explanations for the reduced PM2.5 concentrations on inversion days. Weekday and seasonal analysis, with associated meteorological parameters are also discussed.

An investigation of air pollution in southern Ontario, Canada, with MODIS and MISR Aerosol Data

On October 3-5, 2005 a smog advisory was issued for southern Ontario,Canada, due to high ground-level ozone and fine particulate matter (particles less than 2.5 microns in diameter - PM 2.5). Warm temperatures up to 28 C, high humidity and gentle winds contributed to a build-up of pollutants locally. In addition, southerly winds transported pollutants from the neighbouring United States northward into Canada. Data from the Moderate Resolution Imaging Spectroradiometer (MODIS) were obtained for four days - October 1st, 3rd, 4th, and 5th, 2005. The transport of high aerosol loadings northward across the Great Lakes is clearly evident on the images. We used linear regression analysis to investigate the relationship between MODIS aerosol optical depth (AOD) and ground-level PM2.5 during this period. The results suggest that a strong relationship is derived when meteorological variables are included in the regression model. An R2 value of 0.76 was obtained with MODIS AOD, average temperature, wind speed and relative humidity variables included as predictors of PM2.5.

Effective mitigation efforts to reduce road dust near industrial sites: Assessment by mobile pollution surveys

Assessment of spatial variation of fugitive dust sources, particularly road dust track-out from industrial sites and its subsequent re-suspension is difficult with fixed air quality monitoring stations given their sparse distribution and the highly localized nature of road dust. Mobile monitoring was employed to measure levels of road dust in the industrial area of the City of Hamilton, Ontario, Canada. Results of this monitoring were used in a Fugitive Dust Control workshop held for local stakeholders, where fugitive dust control solutions were presented. After the workshop, the City of Hamilton and cooperative industrial groups executed enhanced street cleaning and individual industries and facilities performed on-site control activities. Post-workshop mobile air monitoring was performed for comparison to the initial values to determine effectiveness of these approaches. A regression model testing the difference pre- and post-workshop yielded a statistically significant difference in PM(10) measurements demonstrating improvement. The average value of PM(10) prior to the workshop was 114 μg/m(3). Post-workshop the average value dropped to 73 μg/m(3).

Proximity to major roadways is a risk factor for airway hyper-responsiveness in adults.

BACKGROUND Proximity to major roads is reported to be associated with asthma and airway hyper-responsiveness in children. Similar studies using objective measurements in adults are not available in Canada. OBJECTIVE To test the hypothesis that adult asthmatic patients who live close to major roads and highways in an urban environment are at a risk of moderate to severe airway hyper-responsiveness. METHODS Airway responsiveness was determined using methacholine bronchial provocation (PC(20)) tests in a cohort of 2625 patients who attended an outpatient clinic in Hamilton, Ontario. Patient addresses were geocoded in a geographic information system to determine proximity to major roads and highways. Multivariate linear and multinomial regression analyses were used to assess whether proximity to roads was a risk factor for airway hyper-responsiveness as measured by PC(20) methacholine. RESULTS Patients who lived within 200 m of a major road had increased odds (OR 1.38 [95% CI 1.04 to 1.85]) of having moderate airway hyperresponsiveness (0.25 mg⁄mL 16 mg/mL). Spatial analysis also revealed that the majority of patients with severe airway hyper-responsiveness lived within the urban core of the city while those with moderate to mild hyper-responsiveness were also dispersed in rural areas. CONCLUSIONS In an adult population of patients attending an outpatient respiratory clinic in Hamilton, living close to major roadways was associated with an increased risk of moderate airway hyper-responsiveness. This correlation suggests that exposure to traffic emissions may provoke the pathology of airway hyper-responsiveness leading to variable airflow obstruction.

Weekday and Seasonal Variations in NO 2 in Southern Ontario, Canada using Data from the Ozone Monitoring Instrument (OMI)

Data from the Ozone Monitoring Instrument (OMI) are used to investigate the weekday and seasonal variations in nitrogen dioxide (NO2) densities observed over southern Ontario, Canada. Total column and tropospheric density data gridded at 1deg times 1deg follow the weekday pattern observed by fixed monitoring stations on the ground, with decreased concentration on the weekends and highest values during mid-week. While seasonal patterns from tropospheric data are similar to ground observations, the total column vertical density pattern shows a summer NO2 peak. Additional higher resolution tropospheric data, gridded at 0.25deg times 0.25deg for a smaller area encompassing the city of Hamilton, Ontario, show weekly and seasonal patterns which conform closely to those observed on the ground. While univariate linear regression indicate that OMI tropospheric NO2 explain only 20% of ground observations (R2 = 0.20), multivariate analyses with variables representing local meteorology, seasons and other pollutants, yield an R2 value of 0.81.

Human cellular response to temperature inversions detected by the Atmospheric Infrared Sounder (AIRS)

Temperature inversions cause restricted air flow, leading to a buildup of air pollution below the inversion cap. This accumulation often leads to levels exceeding air quality standards. Recent studies have shown that some types of inflammatory cells in the respiratory system respond to exposure to air pollution. The cellular response includes a statistically significant increase in the number of cells or the relative proportion of specific cells. We investigate whether these inflammatory cells exhibit a response on temperature inversion days, when the air pollution levels are enhanced. We identify temperature inversions with vertical profiles from the Atmospheric Infrared Sounder (AIRS). The study area is the Hamilton Census Metropolitan Area, Ontario, Canada.

Use of the Atmospheric Infrared Sounder (AIRS) Surface Skin and Air Temperature Data Over Rural and Urban-Industrial Regions in Canada and the USA

We investigate the changes in surface air and skin temperatures for the period 2003 to 2007 over southern Ontario, Canada and bordering US States, as well as two urban-industrial and one rural sub-region. Surface air and skin temperatures acquired by the Atmospheric Infrared Sounder (AIRS) were used. The data indicate an overall increase in all temperatures for all areas, over the period. Both minimum and maximum temperatures are increasing, but minimum temperatures appear to be increasing at a faster rate in rural areas. There is also an indication that nighttime skin temperature is increasing faster than nighttime air temperature, so that there is a convergence of these two temperatures. In the urban areas, the daytime air temperature is increase marginally faster than the daytime skin temperature. This is contrary to the pattern in the rural areas, and is indicative of the effect of human activity on air temperature during the daytime. The data also indicate that during periods of daytime temperature inversions, the air temperature is warmer than the skin temperature, in both urban and rural areas.