title: Associations between daily mortality in London and combined oxidant capacity, ozone and nitrogen dioxide.
abstract: Both nitrogen dioxide (NO2) and ozone (O3) are powerful oxidants in ambient air that are intimately linked through atmospheric chemistry and which continuously interchange over very short timescales. Based upon atmospheric chemistry alone, there is a strong, a priori, reason for considering O3and NO2together in epidemiological studies, rather than either of the two pollutants separately in single-pollutant models. This paper compares two approaches to this, using Ox, defined as O3+ NO2, as a single metric and also using O3and NO2together in two-pollutant models. We hypothesised that the magnitude of the association between Oxand daily mortality would be greater than for NO2and O3individually. Using collocated hourly measurements for O3and NO2in London, from 2000 to 2005, we carried out a time series analysis of daily mortality. We investigated O3, NO2and Oxindividually in single-pollutant Poisson regression models and NO2and O3jointly in two-pollutant models in both all-year and season-specific analyses. We observed larger associations for mean 24-h concentrations of Ox(1.30 % increase in mortality per 10 ppb) than for O3(0.87 %) and NO2(0 %) individually. However, when analysed jointly in two-pollutant models, associations for O3(1.54 %) and NO2(1.07 %) were comparable to the Oxassociation. Season-specific analyses broadly followed this pattern irrespective of whether the Oxconcentrations were driven by O3production (summer) or depletion (winter). This novel approach in air pollution epidemiology captures the simultaneous impact of both oxidants whilst avoiding many of the statistical issues associated with two-pollutant models and potentially simplifies health impact calculations.
authors.affiliation: MRC-PHE Centre for Environment and Health, Kings College London, Room 4.129 Franklin Wilkins Building, 150 Stamford Street, London, SE1 9NH UK.
authors.forename: M L
authors.initials: ML
authors.lastname: Williams
authors.affiliation: Public Health Research Institute and MRC-PHE Centre for Environment and Health, St George's, University of London, London, UK.
authors.forename: R W
authors.initials: RW
authors.lastname: Atkinson
authors.affiliation: Public Health Research Institute and MRC-PHE Centre for Environment and Health, St George's, University of London, London, UK ; MRC-PHE Centre for Environment and Health, Kings College London, Franklin Wilkins Building, 150 Stamford Street, London, SE1 9NH UK.
authors.forename: H R
authors.initials: HR
authors.lastname: Anderson
authors.affiliation: MRC-PHE Centre for Environment and Health, Kings College London, Franklin Wilkins Building, 150 Stamford Street, London, SE1 9NH UK.
authors.forename: F J
authors.initials: FJ
authors.lastname: Kelly
keywords: Mortality; Nitrogen dioxide; Oxidants; Ozone; Time series