A comparison of short-term and long-term air pollution exposure associations with mortality in two cohorts in Scotland

Air pollution–mortality risk estimates are generally larger at longer-term, compared with short-term, exposure time scales. We compared associations between short-term exposure to black smoke (BS) and mortality with long-term exposure–mortality associations in cohort participants and with short-term exposure–mortality associations in the general population from which the cohorts were selected. We assessed short-to-medium–term exposure–mortality associations in the Renfrew–Paisley and Collaborative cohorts (using nested case–control data sets), and compared them with long-term exposure–mortality associations (using a multilevel spatiotemporal exposure model and survival analyses) and short-to-medium–term exposure–mortality associations in the general population (using time-series analyses). For the Renfrew–Paisley cohort (15,331 participants), BS exposure–mortality associations were observed in nested case–control analyses that accounted for spatial variations in pollution exposure and individual-level risk factors. These cohort-based associations were consistently greater than associations estimated in time-series analyses using a single monitoring site to represent general population exposure {e.g., 1.8% [95% confidence interval (CI): 0.1, 3.4%] vs. 0.2% (95% CI: 0.0, 0.4%) increases in mortality associated with 10-μg/m3 increases in 3-day lag BS, respectively}. Exposure–mortality associations were of larger magnitude for longer exposure periods [e.g., 3.4% (95% CI: –0.7, 7.7%) and 0.9% (95% CI: 0.3, 1.5%) increases in all-cause mortality associated with 10-μg/m3 increases in 31-day BS in case–control and time-series analyses, respectively; and 10% (95% CI: 4, 17%) increase in all-cause mortality associated with a 10-μg/m3 increase in geometic mean BS for 1970–1979, in survival analysis]. After adjusting for individual-level exposure and potential confounders, short-term exposure–mortality associations in cohort participants were of greater magnitude than in comparable general population time-series study analyses. However, short-term exposure–mortality associations were substantially lower than equivalent long-term associations, which is consistent with the possibility of larger, more persistent cumulative effects from long-term exposures

The impact of speciated VOCs on regional ozone increment derived from measurements at the UK EMEP supersites between 1999 and 2012

The impact of 27 volatile organic compounds (VOCs) on the regional O3 increment was investigated using measurements made at the UK EMEP supersites Harwell (1999–2001 and 2010–2012) and Auchencorth (2012). Ozone at these sites is representative of rural O3 in south-east England and northern UK, respectively. The monthly-diurnal regional O3 increment was defined as the difference between the regional and hemispheric background O3 concentrations, respectively, derived from oxidant vs. NOx correlation plots, and cluster analysis of back trajectories arriving at Mace Head, Ireland. At Harwell, which had substantially greater regional O3 increments than Auchencorth, variation in the regional O3 increment mirrored afternoon depletion of anthropogenic VOCs due to photochemistry (after accounting for diurnal changes in boundary layer mixing depth, and weighting VOC concentrations according to their photochemical ozone creation potential). A positive regional O3 increment occurred consistently during the summer, during which time afternoon photochemical depletion was calculated for the majority of measured VOCs, and to the greatest extent for ethene and m+p-xylene. This indicates that, of the measured VOCs, ethene and m+p-xylene emissions reduction would be most effective in reducing the regional O3 increment but that reductions in a larger number of VOCs would be required for further improvement. The VOC diurnal photochemical depletion was linked to anthropogenic sources of the VOC emissions through the integration of gridded anthropogenic VOC emission estimates over 96 h air-mass back trajectories. This demonstrated that one factor limiting the effectiveness of VOC gridded emissions for use in measurement and modelling studies is the highly aggregated nature of the 11 SNAP (Selected Nomenclature for Air Pollution) source sectors in which they are reported, as monthly variation in speciated VOC trajectory emissions did not reflect monthly changes in individual VOC diurnal photochemical depletion. Additionally, the major VOC emission source sectors during elevated regional O3 increment at Harwell were more narrowly defined through disaggregation of the SNAP emissions to 91 NFR (Nomenclature for Reporting) codes (i.e. sectors 3D2 (domestic solvent use), 3D3 (other product use) and 2D2 (food and drink)). However, spatial variation in the contribution of NFR sectors to parent SNAP emissions could only be accounted for at the country level. Hence, the future reporting of gridded VOC emissions in source sectors more highly disaggregated than currently (e.g. to NFR codes) would facilitate a more precise identification of those VOC sources most important for mitigation of the impact of VOCs on O3 formation. In summary, this work presents a clear methodology for achieving a coherent VOC, regional-O3-impact chemical climate using measurement data and explores the effect of limited emission and measurement species on the understanding of the regional VOC contribution to O3 concentrations

Sources and contributions of wood smoke during winter in London: Assessing local and regional influences

Determining the contribution of wood smoke to air pollution in large cities such as London is becoming increasingly important due to the changing nature of domestic heating in urban areas. During winter, biomass burning emissions have been identified as a major cause of exceedances of European air quality limits. The aim of this work was to quantify the contribution of biomass burning in London to concentrations of PM2:5 and determine whether local emissions or regional contributions were the main source of biomass smoke. To achieve this, a number of biomass burning chemical tracers were analysed at a site within central London and two sites in surrounding rural areas. Concentrations of levoglucosan, elemental carbon (EC), organic carbon (OC) and KC were generally well correlated across the three sites. At all the sites, biomass burning was found to be a source of OC and EC, with the largest contribution of EC from traffic emissions, while for OC the dominant fraction included contributions from secondary organic aerosols, primary biogenic and cooking sources. Source apportionment of the EC and OC was found to give reasonable estimation of the total carbon from non-fossil and fossil fuel sources based upon comparison with estimates derived from 14C analysis. Aethalometer-derived black carbon data were also apportioned into the contributions frombiomass burning and traffic and showed trends similar to those observed for EC. Mean wood smoke mass at the sites was estimated to range from 0.78 to 1.0 μgm-3 during the campaign in January–February 2012. Measurements on a 160m tower in London suggested a similar ratio of brown to black carbon (reflecting wood burning and traffic respectively) in regional and London air. Peaks in the levoglucosan and KC concentrations were observed to coincide with low ambient temperature, consistent with domestic heating as a major contributing local source in London. Overall, the source of biomass smoke in London was concluded to be a background regional source overlaid by contributions from local domestic burning emissions. This could have implications when considering future emission control strategies during winter and may be the focus of future work in order to better determine the contributing local sources

Evaluation and calibration of Aeroqual Series 500 portable gas sensors for accurate measurement of ambient ozone and nitrogen dioxide

Low-power, and relatively low-cost, gas sensors have potential to improve understanding of intra-urban air pollution variation by enabling data capture over wider networks than is possible with 'traditional' reference analysers. We evaluated an Aeroqual Ltd. Series 500 semiconducting metal oxide O3 and an electrochemical NO2 sensor against UK national network reference analysers for more than 2months at an urban background site in central Edinburgh. Hourly-average Aeroqual O3 sensor observations were highly correlated (R2=0.91) and of similar magnitude to observations from the UV-absorption reference O3 analyser. The Aeroqual NO2 sensor observations correlated poorly with the reference chemiluminescence NO2 analyser (R2=0.02), but the deviations between Aeroqual and reference analyser values ([NO2]Aeroq-[NO2]ref) were highly significantly correlated with concurrent Aeroqual O3 sensor observations [O3]Aeroq. This permitted effective linear calibration of the [NO2]Aeroq data, evaluated using 'hold out' subsets of the data (R2≥0.85). These field observations under temperate environmental conditions suggest that the Aeroqual Series 500 NO2 and O3 monitors have good potential to be useful ambient air monitoring instruments in urban environments provided that the O3 and NO2 gas sensors are calibrated against reference analysers and deployed in parallel

Using archive data to investigate trends in the sources and composition of urban PM10 particulate matter : application to Edinburgh (UK) between 1992 and 1997

By extending the method of Stedman (1998), daily data of atmospheric concentrations of gravimetric PM10, black smoke (BS) and sulphate aerosol (SA) from national networks were analysed to determine the trends in time of the contribution of different sources of particulate matter to total PM10 measured in central Edinburgh. Since BS is an indicator of combustion-related primary sources of particulate matter, the quantity obtained by subtraction of daily BS from daily PM10 is indicative of the contribution to total PM10 from other primary sources and from secondary aerosol. This PM10-BS statistic was regressed on SA, since SA is an indicator of variation in secondary aerosol source. For Edinburgh, SA is a considerably better indicator of PM10-BS during summer than winter (reflecting the much greater photochemical generation of secondary aerosol in summer) and there is evidence that the contribution of other secondary aerosol (presumably nitrate aerosol) has increased relative to SA between 1992 and 1997. The concentration of non-combustion primary particulate material (marine aerosol, suspended dust) to PM10 in Edinburgh has not changed over this period but is about twice that calculated as the U.K. national average. The increasing input to PM10 from secondary aerosol sources at regional rather than urban scale has important implications for ensuring local air quality compliance. The method should have general applicability to other locations

Correlations of particle number concentrations and metals with nitrogen oxides and other traffic-related air pollutants in Glasgow and London

Particle number concentration (PNC) and transition metal content are implicated in the health effects of airborne particulate matter (PM) but they are difficult to measure so consequently their temporal and spatial variations are not well characterized. Daily concentrations of PNC and particle-bound water-soluble metals (V, Cr, Mn, Fe, Ni, Cu, As, Cd and Pb) were measured at background and kerbside sites in Glasgow and London to examine if other metrics of air pollution such as optical darkness (absorbance) of collected filter samples of PM, gravimetric PM, and NO, NO2 and CO gas concentrations, can be used as surrogates for the temporal and spatial variations of the former. NO2 and NOx exhibited a high degree of within-site correlation and with PNC and water-soluble metals (Fe, Cu, As, Cd, Pb) at background sites in both cities. There is therefore potential to use NO2 and NOx as surrogates for PNC and water-soluble metal at background sites. However, correlation was weaker in complex street canyon environments where pollutant concentrations are strongly affected by local sources and the small-scale variations in pollutant dispersion induced by the wind regimes within street canyons. The corollary of the high correlation between NO2 and PNC and water-soluble metals at the background sites is that the latter pollutants may act as confounders for health effects attributed to NO2 from such sites. Concentrations of CO cannot be used as a surrogate for PNC. Increments in daily NOx and NO2 concentrations between trafficked and background sites were shown to be a simple and novel surrogate for daily spatial variation of PNC; for example, increments in NOx explained 78–79% of the variance in PNC at the paired sites in both Glasgow and London, but relationships were city specific. The increments in NOx also explained 70% of the spatial variation in Cu and Ni in Glasgow but not in London. Weekly NO2 measurements derived from passive diffusion tubes were also shown to correlate well with increments in PNC. A high temporal correlation between PNC and 1,3-butadiene and benzene (which can also be measured by passive sampler) implies that passive sampler measurements may be a straightforward tool for deriving long-term spatial patterns in PNC

Development of PTR-MS selectivity for structural isomers: monoterpenes as a case study

Proton-Transfer-Reaction Mass Spectrometry (PTR-MS) is a very useful tool for high frequency detection and quantification of gas-phase volatile organic compounds (VOCs) but the soft ionization means it is difficult to discriminate structural isomers. For example, to date it has only been possible to measure the sum of monoterpene concentrations, which have been monitored most commonly at m/z 81 and 137 at a constant drift voltage and pressure. We show here that PTR-MS is capable of discriminating individual monoterpenes when operating in the alternating drift voltage (AD) mode. The approach is based on the principle that slightly different energies are required for the fragmentation/clustering of a given monoterpene, so in AD mode each monoterpene has different time points for fragmentation. Therefore from a fragmentation analysis of background-subtracted standards it is possible to calculate the percentage of each monoterpene in an absolute concentration of their sum. Although monoterpenes have been chosen as an example, the method is likely to be effective for other structural isomeric species such as the sesquiterpenes or methyl vinyl ketone/methacrolein (MVK/MACR)

Total and water-soluble trace metal content of urban background PM10, PM2.5 and black smoke in Edinburgh, UK

Toxicological studies have implicated trace metals in airborne particles as possible contributors to respiratory and/or cardiovascular inflammation. As part of an epidemiological study, co-located 24 h samples of PM10, PM2.5 and black smoke (BS) were collected for 1 year at an urban background site in Edinburgh, and each sample sequentially extracted with ultra-pure water, then concentrated HNO3/HCl, and analysed for Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Cd and Pb. This yields a comprehensive data set for UK urban airborne trace metal. The median (n>349) daily water-soluble metal concentration in PM2.5 ranged from 0.05 ng m−3 for Ti to 5.1 ng m−3 for Pb; and in PM10 from 0.18 ng m−3 for Ti to 11.7 ng m−3 for Fe. Median daily total (i.e. water+acid-extractable) metal concentration in PM2.5 ranged from 0.3 ng m−3 for As to 27.6 ng m−3 for Fe; and in PM10 from 0.37 ng m−3 for As to 183 ng m−3 for Fe. The PM2.5:PM10 ratio varied considerably with metal, from 70% for V, As, Cd and Pb. The 11 trace metals constituted proportionally more of the PM10-2.5 fraction than of the PM2.5 fraction (0.9%). The proportion of water-soluble metal in each size-fraction varied considerably, from 50% water-soluble V, Zn, As and Cd in PM2.5. Although Fe generally dominated the trace metal, water-soluble metal also contained significant Zn, Pb and Cu, and for all size and solubility fractions >90% of trace metal was comprised of Fe, Zn, Pb and Cu. Statistical analyses suggested three main sources: traffic; static combustion; and crustal. The association of metals with traffic (Cu, Fe, Mn, Pb, Zn) was consistent with traffic-induced non-exhaust "resuspension" rather than direct exhaust emission. Meteorology contributed to the wide variation in daily trace metal concentration. The proportion of trace metal in particles varied significantly with the air mass source and was highest on days for trajectories traversing over land. For Mn, Fe, Cu, Zn, As and Pb there was greater correlation of metal concentration with BS mass than with either PM10 or PM2.5 mass, suggesting that BS reflectance monitoring could be a cost-effective surrogate measure of particle metal concentration in urban background air

Interpretation of variations in fine, coarse and black smoke particulate matter concentrations in a northern European city

The PM2.5, PMcoarse and black smoke (BS) particle metrics broadly reflect different source contributions to PM10. The aim of this study was to generate data for PM2.5 at an urban background site in the UK, and to use the daily collocated measurement of PM2.5, PM10 (and hence PMcoarse) and BS to yield insight into source influences on particulate matter for input to developing PM air quality policy. Mean daily PM10, PM2.5 and BS for a year of measurement in Edinburgh were 15.5, 8.5 and 6.6 mu g m(-3). The PM2.5 data were well-within possible future limit values proposed by the European Commission Clean Air For Europe programme. Daily PM2.5 and PM10 were significantly correlated (r(2) = 0.75) with PM2.5 contributing 54%, on average, to PM10. The daily BS:PM10 and BS:PM2.5 ratios were more variable, and significantly lower in summer than in winter, reflecting the greater contribution of non-black photochemical secondary particles to PM10 in summer. Analysis with respect to wind showed a dominant influence of dispersion on BS and PM2.5 but both dispersion and a wind-driven suspension influence on PMcoarse. The latter was higher than in central England (Averaging about one-third of the PMcoarse), and greater for on-shore wind direction, suggesting a sea-salt source for this component in addition to other particle resuspension contributions. Overall, the data showed that excursions in PM10 were driven more by variations in PM2.5 than by PMcoarse or BS. Both PM2.5 and its proportion to PM10 were significantly elevated for aid-masses passing over continental Europe and the British Isles, whereas BS varied less with air-mass origin, supporting the conclusion that concentrations of particulate matter, particularly of finer PM, are strongly influenced by regional scale synoptic meteorology (presumed to be predominantly secondary PM), whereas BS is dominated more by local sources. Comparison of BS with a nearby rural site suggested that approximately three-quarters, on average, of the urban BS was local in origin