Spatial modeling of daily concentrations of ground-level ozone in Montreal, Canada: A comparison of geostatistical approaches.

Ground-level ozone (O3) is a powerful oxidizing agent and a harmful pollutant affecting human health, forests and crops. Estimating O3 exposure is a challenge because it exhibits complex spatiotemporal patterns. The aim in this study was to provide high-resolution maps (100 × 100 m) of O3 for the metropolitan area of Montreal, Canada. We assessed the kriging with external drift (KED) model to estimate O3 concentration by synoptic weather classes for 2010. We compared these results with ordinary kriging (OK), and a simple average of 12 monitoring stations. We also compared the estimates obtained for the 2010 summer with those from a Bayesian maximum entropy (BME) model reported in the literature (Adam-Poupart et al., 2014). The KED model with road and vegetation density as covariates showed good performance for all six synoptic classes (daily R2 estimates ranging from 0.77 to 0.92 and RMSE from 2.79 to 3.37 ppb). For the summer of 2010, the model using KED demonstrated the best results (R2 = 0.92; RMSE = 3.14 ppb), followed by the OK model (R2 = 0.85, RMSE = 4 ppb). Our results showed that errors appear to be substantially reduced with the KED model. This may increase our capacity of linking O3 levels to health problems by means of improved assessments of ambient exposures. However, future work integrating the temporal dependency in the data is needed to not overstate the performance of the KED model.

Should we use absolute or relative measures when assessing foodscape exposure in relation to fruit and vegetable intake? Evidence from a wide-scale Canadian study.

OBJECTIVE: This paper explores which of absolute (i.e. densities of "healthy" and "unhealthy" food outlets taken separately) or relative (i.e. the percentage of "healthy" outlets) measures of foodscape exposure better predicts fruit and vegetable intake (FVI), and whether those associations are modified by gender and city in Canada. METHODS: Self-reported FVI from participants of four cycles (2007-2010) of the repeated cross-sectional Canadian Community Health Survey living in the five largest metropolitan areas of Canada (n=49,403) was analyzed. Absolute and relative measures of foodscape exposure were computed at participants' residential postal codes. Linear regression models, both in the whole sample and in gender- and city-stratified samples, were used to explore the associations between exposure measures and FVI. RESULTS: The percentage of healthy outlets was strongly associated with FVI among men both in Toronto/Montreal (ß=0.012; P<0.001), and in Calgary/Ottawa/Vancouver (ß=0.008; P<0.001), but not among women. Observed associations of absolute measures with FVI were either weak or faced multicollinearity issues. Overall, models with the relative measure showed the best fit. CONCLUSIONS: Relative measures should be more widely used when assessing foodscape influences on diet. The absence of a single effect of the foodscape on diet positions sub-group analysis as a promising avenue for research.

[Not Available]. / Relations spatiales entre les caractéristiques des territoires et les taux d'enfants de groupes ethnoculturels signalés à la protection de la jeunesse.

OBJECTIVES: The objectives of this study were to 1) map the geographic distribution of rates of children reported to Montreal child protective services by ethnocultural group (Black, other visible minorities, not from visible minorities) and 2) estimate the relative contribution of different territorial characteristics to the rates for those groups. METHOD: The study covered the 505 Montreal-area census tracts for which complete data were available. The reporting rates by group (dependent variables) and various territorial characteristics such as poverty (independent variables) were mapped and subjected to multiple linear regression and geographically weighted regression. The results of the geographically weighted regression were then mapped. RESULTS: The geographic distribution and reporting rates varied greatly by group, with the Black children having the highest rates. Although territorial characteristics explained 51% of variance for the children who were not members of visible minorities, they were clearly less effective in predicting rates in the case of Black children (18%) and other minorities (18%). CONCLUSION: Already well-known territorial risk factors are at work in Montreal, but their influence is not equally strong in all census tracts nor, especially, in all ethnocultural groups. Therefore, when only the distribution and prediction of reports for all children as a whole are examined, important differences are underestimated. Access to and appropriateness of services offered to vulnerable families, including those of visible minorities, could, however, be improved with a better understanding of local dynamics.

Spatio-temporal models to estimate daily concentrations of fine particulate matter in Montreal: Kriging with external drift and inverse distance-weighted approaches.

Air pollution is a major environmental and health problem, especially in urban agglomerations. Estimating personal exposure to fine particulate matter (PM2.5) remains a great challenge because it requires numerous point measurements to explain the daily spatial variation in pollutant levels. Furthermore, meteorological variables have considerable effects on the dispersion and distribution of pollutants, which also depends on spatio-temporal emission patterns. In this study we developed a hybrid interpolation technique that combined the inverse distance-weighted (IDW) method with Kriging with external drift (KED), and applied it to daily PM2.5 levels observed at 10 monitoring stations. This provided us with downscaled high-resolution maps of PM2.5 for the Island of Montreal. For the KED interpolation, we used spatio-temporal daily meteorological estimates and spatial covariates as land use and vegetation density. Different KED and IDW daily estimation models for the year 2010 were developed for each of the six synoptic weather classes. These clusters were developed using principal component analysis and unsupervised hierarchical classification. The results of the interpolation models were assessed with a leave-one-station-out cross-validation. The performance of the hybrid model was better than that of the KED or the IDW alone for all six synoptic weather classes (the daily estimate for R(2) was 0.66-0.93 and for root mean square error (RMSE) 2.54-1.89 µg/m(3)).

The role of living context in prescription opioid injection and the associated risk of hepatitis C infection.

BACKGROUND AND AIMS: Prescription opioid injection (POI) is a leading risk factor for hepatitis C virus (HCV). Residential context relates to high­risk injection behaviour. This study assessed whether residence in the inner city (versus surrounding areas in Montréal Island) modified the effects of correlates of POI or the relationship between POI and HCV incidence. DESIGN: Prospective cohort study. SETTING: Montréal, Canada. PARTICIPANTS: A total of 854 people who inject drugs (18% female, 25% age < 30 years), living on Montréal Island, were interviewed every 3­6 months from 2004 to 2012. MEASUREMENTS: Study visits included HCV antibody testing and an interviewer­administered questionnaire. Generalized estimating equations were used to test whether place of residence modified the effects of correlates of POI. Cox regression was used to test whether place of residence modified the relationship between POI and HCV incidence. FINDINGS: At baseline, inner­city participants were more likely to report POI in the past month (40 versus 25%, P < 0.001). The association between POI and heroin injection, syringe sharing and sharing of injecting equipment varied according to place of residence and was greater in the inner city. The hazard of HCV infection associated with POI was greater among inner­city participants compared to those in the surrounding areas [adjusted hazard ratio (HR) = 3.38, 95% confidence interval (CI) = 1.88­6.07 versus HR = 1.26, 95% CI = 0.65­2.42, P = 0.025]. CONCLUSIONS: Among people who inject prescription opioids in Montréal, Canada, those who live in inner­city areas are more likely to engage in injecting­related risk behaviours and have a higher risk of hepatitis C virus infection than those who live in the suburbs.