Updated recommendations for quantifying hospital admissions associated with short-term exposures to air pollutants
22 March 2022
The Committee on the Medical Effects of Air Pollutants (COMEAP) have announced they are updating their recommendations for quantification of hospital admissions associated with short-term exposures to air pollutants, specifically particulate matter (PM), nitrogen dioxide (NO2) and ozone (O3). These recommendations are intended to inform cost-benefit analyses that will be undertaken to support the development of air quality targets under the Environment Act 2021, formerly the Environment Bill 2020. COMEAP have adopted an approach to evaluating the evidence which has allowed revised recommendations to be made in a timely manner.
Recent meta-analyses of studies evaluating the associations between (total, all-cause) respiratory and cardiovascular hospital admissions and short-term exposures to PM, NO2 and O3 have been examined and COMEAP have further considered summary effects estimates (coefficients) from single pollutant models derived in meta-analyses of the global literature, undertaken by St George’s, University of London, as the most suitable for use as concentration-response functions to quantify hospital admissions associated with short-term exposures to air pollutants.
COMEAP recommend that the 24-hour effect estimates for NO2 are used in health impact assessments of interventions to improve air quality. However, concentration response functions for one-hour average concentrations of NO2 might be appropriate for some uses.
Concentrations of PM2.5 and NO2 are often highly correlated, meaning that associations reported from epidemiological studies likely reflect the effect of both pollutants to some extent. Therefore, using coefficients for both PM2.5 and NO2, for the same health endpoint, within the same assessment would result in an over-estimation of the effect of the air pollution mixture, or of the benefits of interventions to reduce emissions. However, on balance, COMEAP consider that the coefficients for all-year O3 are likely to be independent of those for either PM2.5 or NO2, meaning that that there is less concern about possible over-estimation when using them in a combined assessment. In addition, policy makers should be aware that localised interventions designed to reduce NO2 may have the unintended consequence of increasing localised concentrations of O3.
COMEAP also draw attention to the uncertainties regarding causality for some pollutant-outcome pairs, notably cardiovascular hospital admissions associated with NO2, as these uncertainties will need to be considered when deciding which pollutant-outcome pairs to include in core assessments or in sensitivity analyses.