DISCORDANCE BETWEEN ONE-HOUR AND ANNUAL LIMITS OF THE WORLD HEALTH ORGANIZATION AIR QUALITY GUIDELINE (WHOAQG) FOR NO2

Abstract

Background and Aims: It is important to ensure the short-term and annual AQG are valid and robust to provide support to setting standards which, if enforced, will reliably ensure that exposure reduction targets are met effectively for health protection. Methods: We developed a lognormal distribution model to examine the relationship between short-term and annual AQG for NO2 using data in 2010 in Hong Kong and London. This model, which takes into account the allowable exceedances of AQG, was robust after extreme values (4 times the geometric standard deviation above the geometric mean) were excluded [2]. Results: The WHOAQG of 40•g/m cannot be achieved through compliance with short-term limit of 200•g/m. The predicted 1hr AQG is sensitive to the standard deviation of the ambient mass concentration, and estimated to be 140•g/m and 128•g/m in Hong Kong and London respectively. In the model validation using WHO 24-hr AQG for PM10 / PM2.5, we obtained reliable prediction of annual AQG for PM10 (21.5•g/m ) and PM2.5 (10.3•g/m ) in Hong Kong. Conclusions: The large difference between WHO 1-hr limit (200•g/m) and the predicted limit indicates statistical discordance between the short-term and annual NO2 limits in the current WHOAQG, in contrast to other criteria pollutants. Based on public health principles, the shortand long-term epidemiologic evidence and need to ensure validity of health impact assessments, the 1-hr AQG should be between 128 and 140•g/m given the standard deviations observed in typical traffic dense environments. Factors affecting the standard deviation may include number of monitors, sampling locations, pollution sources, and meteorological factors. Data from other cities is needed.