Background: Winter temperature inversions—layers of air in which temperature increases with altitude—trap air pollutants and lead to higher pollutant concentrations. Previous studies have evaluated associations between pollutants and emergency department (ED) visits for asthma, but none have considered inversions as independent risk factors for ED visits for asthma.Objective: We aimed to assess associations between winter inversions and ED visits for asthma in Salt Lake County, Utah.Methods: We obtained electronic records of ED visits for asthma and data on inversions, weather, and air pollutants for Salt Lake County, Utah, during the winters of 2003 through 2004 to 2007 through 2008. We identified 3,425 ED visits using a primary diagnosis of asthma. We used a time-stratified case-crossover design, and conditional logistic regression models to calculate odds ratios (ORs) and 95% confidence intervals (CIs) to estimate rate ratios of ED visits for asthma in relation to inversions during a 4-day lag period and prolonged inversions. We evaluated interactions between inversions and weather and pollutants.Results: After adjusting for dew point and mean temperatures, the OR for ED visits for asthma associated with inversions 0–3 days before the visit compared with no inversions during the lag period was 1.14 (95% CI: 1.00, 1.30). The OR for each 1-day increase in the number of inversion days during the lag period was 1.03 (95% CI: 1.00, 1.07). Associations were only apparent when PM10 and maximum and mean temperatures were above median levels.Conclusions: Our results provide evidence that winter inversions are associated with increased rates of ED visits for asthma.

The investigation encompassed by this report is an attempt to assess the potential for commercial development of peat moss from some of the most important known peat deposits in the southern part of the province of Ontario. The authors' examination of the fourteen bogs selected and described was concentrated on procedures which it was thought would allow best assessment of the deposits in this regard. Prominent among the factors considered are moss quality as determined by analytical methods, accessibility, location, topography, drainage, area, type of growth, and depth of the bog.

In this report, seventeen peat bogs in the Rainy River District of Ontario are illustrated by aerial photographs and are assessed from the viewpoints of location, access, area, depth, cover, drainage and nature of the peat material present. The locations of several other bogs in the district are noted. Analytical procedures and the importance of sampling are emphasized in this demonstration of the methodology of evaluating the potential of peat bogs for commercial development.