A Review of Urban Air Pollution Monitoring and Exposure Assessment Methods <s> Inverse Distance Weighting <s> BACKGROUND ::: Long-term exposure to particulate matter air pollution has been associated with increased cardiopulmonary mortality in the USA. We aimed to assess the relation between traffic-related air pollution and mortality in participants of the Netherlands Cohort study on Diet and Cancer (NLCS), an ongoing study. ::: ::: ::: METHODS ::: We investigated a random sample of 5000 people from the full cohort of the NLCS study (age 55-69 years) from 1986 to 1994. Long-term exposure to traffic-related air pollutants (black smoke and nitrogen dioxide) was estimated for the 1986 home address. Exposure was characterised with the measured regional and urban background concentration and an indicator variable for living near major roads. The association between exposure to air pollution and (cause specific) mortality was assessed with Cox's proportional hazards models, with adjustment for potential confounders. ::: ::: ::: FINDINGS ::: 489 (11%) of 4492 people with data died during the follow-up period. Cardiopulmonary mortality was associated with living near a major road (relative risk 1.95, 95% CI 1.09-3.52) and, less consistently, with the estimated ambient background concentration (1.34, 0.68-2.64). The relative risk for living near a major road was 1.41 (0.94-2.12) for total deaths. Non-cardiopulmonary, non-lung cancer deaths were unrelated to air pollution (1.03, 0.54-1.96 for living near a major road). ::: ::: ::: INTERPRETATION ::: Long-term exposure to traffic-related air pollution may shorten life expectancy. <s> BIB001 </s> A Review of Urban Air Pollution Monitoring and Exposure Assessment Methods <s> Inverse Distance Weighting <s> RATIONALE ::: Although substantial scientific evidence suggests that chronic exposure to ambient air pollution contributes to premature mortality, uncertainties exist in the size and consistency of this association. Uncertainty may arise from inaccurate exposure assessment. ::: ::: ::: OBJECTIVES ::: To assess the associations of three types of air pollutants (fine particulate matter, ozone [O3], and nitrogen dioxide [NO2]) with the risk of mortality in a large cohort of California adults using individualized exposure assessments. ::: ::: ::: METHODS ::: For fine particulate matter and NO2, we used land use regression models to derive predicted individualized exposure at the home address. For O3, we estimated exposure with an inverse distance weighting interpolation. Standard and multilevel Cox survival models were used to assess the association between air pollution and mortality. ::: ::: ::: MEASUREMENTS AND MAIN RESULTS ::: Data for 73,711 subjects who resided in California were abstracted from the American Cancer Society Cancer Prevention II Study cohort, with baseline ascertainment of individual characteristics in 1982 and follow-up of vital status through to 2000. Exposure data were derived from government monitors. Exposure to fine particulate matter, O3, and NO2 was positively associated with ischemic heart disease mortality. NO2 (a marker for traffic pollution) and fine particulate matter were also associated with mortality from all causes combined. Only NO2 had significant positive association with lung cancer mortality. ::: ::: ::: CONCLUSIONS ::: Using the first individualized exposure assignments in this important cohort, we found positive associations of fine particulate matter, O3, and NO2 with mortality. The positive associations of NO2 suggest that traffic pollution relates to premature death. <s> BIB002
Inverse Distance Weighting (IDW) is a deterministic method for spatial interpolation. The value at the unknown location (x, y), u(x, y) is calculated as the weighted average of the measurements at the monitoring stations. This method assumes that the value u(x, y) is more influenced by the close measurements than the distant measurements  . In other words, the close locations get greater weights, and the weights diminish as a function of distance. Given the pollutant measurements at N locations surrounding the unknown location (x, y), u n (x n , y n ), n = 1, . . . N, the value at the unknown location, u(x, y), is calculated as: where i is a commonly squared distance with i chosen as 2. Hoek et al. applied the inverse distance squared weighted interpolation method to estimate the regional concentration of Black Smoke (BS) and Nitrogen Dioxide (NO 2 ), using measurements obtained from stations of the National Air Quality Monitoring Network in Netherlands BIB001 . Their study suggested an association between the cardiopulmonary mortality and living near a major road. Jerrett et al. investigated the influence of personal exposure to ozone (O 3 ), PM 2.5 and NO 2 on human health in California, USA BIB002 . For O 3 , they assessed the monthly exposure over 14 years at 73, 711 residential locations from 262 monitoring sites, using IDW models. They proved that O 3 is significantly associated with cardiovascular mortality, particularly from Ischemic Heart Disease (IHD). Similarly, Beckerman et al. also used IDW interpolation to model the regional exposures of O 3 and PM 2.5 in Toronto, ON, Canada, but found no strong association with IHD. This suggests that the association between cardiovascular disease with a specific air pollutant may be region-dependent. 