Iain J. Beverland

The lagged effect of cold temperature and wind chill on cardiorespiratory mortality in Scotland

Aims: To investigate the lagged effects of cold temperature on cardiorespiratory mortality and to determine whether “wind chill” is a better predictor of these effects than “dry bulb” temperature. Methods: Generalised linear Poisson regression models were used to investigate the relation between mortality and “dry bulb” and “wind chill” temperatures in the three largest Scottish cities (Glasgow, Edinburgh, and Aberdeen) between January 1981 and December 2001. Effects of temperature on mortality (lags up to one month) were quantified. Analyses were conducted for the whole year and by season (cool and warm seasons). Main results: Temperature was a significant predictor of mortality with the strongest association observed between temperature and respiratory mortality. There was a non-linear association between mortality and temperature. Mortality increased as temperatures fell throughout the range, but the rate of increase was steeper at temperatures below 11°C. The association between temperature and mortality persisted at lag periods beyond two weeks but the effect size generally decreased with increasing lag. For temperatures below 11°C, a 1°C drop in the daytime mean temperature on any one day was associated with an increase in mortality of 2.9% (95% CI 2.5 to 3.4), 3.4% (95% CI 2.6 to 4.1), 4.8% (95% CI 3.5 to 6.2) and 1.7% (95% CI 1.0 to 2.4) over the following month for all cause, cardiovascular, respiratory, and “other” cause mortality respectively. The effect of temperature on mortality was not observed to be significantly modified by season. There was little indication that “wind chill” temperature was a better predictor of mortality than “dry bulb” temperature. Conclusions: Exposure to cold temperature is an important public health problem in Scotland, particularly for those dying from respiratory disease.

Measurements of CH4 and N2O fluxes at the landscape scale using micrometeorological methods

Flux gradient, eddy covariance and relaxed eddy accumulation methods were applied to measure CH4 and N2O emissions from peatlands and arable land respectively. Measurements of N2O emission by eddy covariance using tunable diode laser spectroscopy provided fluxes ranging from 2 to 60 µ mol N2O m-2 h-1 with a mean value of 22 µ mol N2O m-2 h-1 from 320 h of continuous measurements. Fluxes of CH4 measured above peatland in Caithness (U.K.) during May and June 1993 by eddy covariance and relaxed eddy accumulation methods were in the range 70 to 120 µ mol CH4 m-2 h-1 with means of 14.7 µ mol CH4 m -2 h-1 and 22.7 µ mol CH4 m-2 h-1 respectively. Emissions of CH4 from peatland changed with water table depth and soil temperature; increasing from 25 |Amol CH4 m-2 h-1 at 5% pool area to 50 p.mol CH4 m-2 h-1 with 30% within the flux footprint occupied by pools. A temperature response of 4.9 (xmol CH4 m-2 h-1 °C-1 in the range 6-12 °C was also observed. The close similarity in average CH4 emission fluxes reported for wetlands in Caithness, Hudson Bay and Alaska in the range 11 to 40 jamol CH4 m-2 h-1 suggests that earlier estimates of CH4 emission from high latitude wetlands were too large or that the area of high latitudes contributing to CH4 emission has been seriously underestimated.

The influence of weather-type and long-range transport on airborne particle concentrations in Edinburgh, UK

This study investigated the influence of regional-scale synoptic weather type and geographical source regions of air masses on two-particle concentration metrics (Black Smoke (BS) and PM10) in the city of Edinburgh, UK, between 1981 and 1996. Twenty-seven classifications of Jenkinson Daily Weather Types (JWT) were sub-divided into 9 directional categories and 3 vorticity categories, and the influence of JWT category on BS and PM10 determined. Four-day air mass back-trajectories for 1 July 1995-30 June 1996 were computed and grouped into 8 categories depending on the geographical route followed. Significantly elevated concentrations of BS (median values 2, 5 and 4 μg m−3 greater than median for 1981-1996) and PM10 (median values 3, 5.5 and 8 μg m−3 greater than median for 1992-1996) were observed for anticyclonic, southerly and south-easterly weather types, respectively. These differences were not identified at conventional levels of significance for BS in 1995-1996. This may reflect a shift in more recent times to lower concentrations of predominantly locally emitted BS less affected by regional scale meteorology. Conversely, significant inter-trajectory category differences were observed for PM10 during 1995-1996, with highest concentrations associated with Eastern European trajectories and south-easterly weather type categories (11.4 and 10.7 μg m−3 greater than annual means, respectively). The variation in particle concentration across weather-type was a significant proportion of total median particle concentration, and of a magnitude associated with adverse health outcomes. Thus current PM10 concentrations (and associated health outcomes) in Edinburgh are likely to be significantly influenced by regional-scale meteorology independent of local air quality management areas. Furthermore, changes in long-term trends in distributions of synoptic weather types indicate that future climate change may influence exposure to PM10 and the PM10:BS ratio in Edinburgh. Further definition of the relationships between long-range transport and particle concentration will improve classification of human exposure in epidemiological studies.

Interacting effects of particulate pollution and cold temperature on cardiorespiratory mortality in Scotland.

Objectives: To determine whether the effect of black smoke on cardiorespiratory mortality is modified by cold temperatures. Methods: Poisson regression models were used to investigate the relationship between lagged black smoke concentration and daily mortality, and whether the effect of black smoke on mortality was modified by cold temperature for three Scottish cities from January 1981 to December 2001. Main results: For all-cause respiratory and non-cardiorespiratory mortality, there was a significant association between mortality and lagged black smoke concentration. Generally the maximum black smoke effect occurred at lag 0, although these estimates were not statistically significant. A 10 μgm−3 increase in the daily mean black smoke concentration on any given day was associated with a 1.68% (95% CI 0.72 to 2.65) increase in all-cause mortality and a 0.43% (95% CI −0.97 to 1.86), 5.36% (95% CI 2.93 to 7.84) and 2.13% (95% CI 0.82 to 3.47) increase in cardiovascular, respiratory and non-cardiorespiratory mortality, respectively, over the ensuing 30-day period. The effect of black smoke on mortality did not vary significantly between seasons (cool and warm periods). For all-cause, cardiovascular and non-cardiorespiratory mortality the inclusion of interaction terms did not improve the models, although for all-cause and non-cardiorespiratory mortality there was a suggestion for interaction between temperature and recent black smoke exposure. Conclusions: The results of this study suggested a greater effect of black smoke on mortality at low temperatures. Since extremes of cold and particulate pollution may coexist, for example during temperature inversion, these results may have important public health implications.

Design, construction and operation of flux measurement systems using the conditional sampling technique

The design, construction and field operation of computer-based systems for the measurement of trace gas fluxes using the conditional sampling technique are described. A simple system which sampled air into sampling bags was used to measure CH4 and N2O fluxes from peatland and agricultural land, respectively. The system was subsequently automated by making real-time measurements of the gas mixing ratios in the sampling lines thus providing continuous measurements for periods of up to several days. Minor modifications enabled measurement of total hydrocarbons, CO2 and non-methane hydrocarbon fluxes from a forest ecosystem. Intercomparison of conditional sampling with other techniques (eddy covariance, gradient and aircraft boundary layer budget) was encouraging with good agreement between flux measurements of CH4, CO2, N2O and sensible heat. The system has been developed in a sufficiently simple and robust manner to enable extended field measurements. A number of theoretical problems remain including the absolute accuracy of the gas analysis procedures and real-time coordinate rotation procedures to deal with non-uniform terrain.

Measurement of nitrous oxide emission from agricultural land using micrometeorological methods

The spatial variability of N2O emission from soil makes extrapolation to the field scale very difficult using; conventional chamber techniques ( < 1 m2). Micrometeorological techniques, which integrate N2O fluxes over areas of 0.1 to 1 km2 were therefore developed and compared with chamber methods over arable cropland. Measurements of N2O emission from an unfertilised organic soil (reclaimed from the sea in 1879) were made over a 10 d period at Lammefjord, Denmark. Flux-gradient and conditional sampling techniques were applied using two tunable diode laser spectrometers (TDLs), a Fourier transform infra-red spectrometer (FTIR) and a gas chromatograph (GC). Eddy covariance measurements were also made by the TDLs. Over the 10 d campaign approximately 5 d of continuous fluxes by the different methods were, obtained. Fluxes determined by eddy covariance were in reasonable agreement, showing a mean flux of 269 μg N m2 h−1. Flux-gradient techniques measured a mean flux of 226 μg N m−2 h−1. The mean flux measured by conditional sampling was 379 μg N m−2 h−1. The maximum annual emission of N2O from this soil system was estimated to be 23.5 kg N ha−1.

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

BACKGROUND Air pollution-mortality risk estimates are generally larger at longer-term, compared with short-term, exposure time scales. OBJECTIVE 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. METHODS 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). RESULTS 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]. CONCLUSIONS 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.

Measurement of Field Scale N2O Emission Fluxes from a Wheat Crop Using Micrometeorological Techniques

Measurements of N2O emission fluxes from a 3 ha field of winter wheat were measured using eddy covariance and relaxed eddy accumulation continuously over 10 days during April 1994. The measurements averaged fluxes over approximately 105 m2 of the field, which was fertilised with NH4NO3 at a rate of 43 kg N ha-1 at the beginning of the measurements. The emission fluxes became detectable after the first heavy rainfall, which occured 4 days after fertiliser application. Emissions of N2O increased rapidly during the day following the rain to a maximum of 280 ng N m-2s-1 and declined over the following week. During the period of significant emission fluxes, a clear diurnal cycle in N2O emission was observed, with the daytime maximum coinciding with the soil temperature maximum at 12 cm depth. The temperature dependence of the N2O emission was equivalent to an activation energy for N2O production of 108 kJ mol-1. The N2O fluxes measured using relaxed eddy accumulation, averaged over 30 to 270 min, were in agreement with those of the eddy covariance system within 60%. The total emission of N2O over the period of continuous measurement (10 days) was equivalent to about 10 kg N2O-N, or 0.77% of the N fertiliser applied.

Measurement of carbon dioxide and hydrocarbon fluxes from a sitka spruce forest using micrometeorological techniques

CO2 and hydrocarbon fluxes from a sitka spruce forest were measured using a conditional sampling method, The method was used in two ways: (1) an automated system was used to monitor continuously the mixing ratio difference of total hydrocarbons and CO2 in sampling lines for updraught and downdraught air and (2) conditionally sampled updraught and downdraught air was passed through adsorption tubes, which subsequently were analyzed in the laboratory, to determine the fluxes of nonmethane hydrocarbons (NMHCs), Aerodynamic gradient measurements of NMHC fluxes were made over the same period. Method (1) produced a high temporal resolution data set of approximately 4 days of near-continuous fluxes. Marked diurnal trends in CO2 flux were evident. Peak daylight photosynthetic fluxes ranged from -30 to -90 mmol m(-2) h(-1). Smaller fluxes were noted during heavy rainfall and diminished photosynthetically active radiation, Nighttime respiration ranged from 0 to 10 mmol m(-2) h(-1). Total hydrocarbon fluxes were 3 orders of magnitude smaller. During hot, sunny conditions a total hydrocarbon flux of approximately 400 mu mol m(-2) h(-1) (CH4 equivalents) was observed, Fluxes of specific NMHC compounds, from method (2), ranged between 90 and 563 mu g m(-2) hour(-1). The annual carbon flux to Great Britains conifer forests was estimated to be 1.3 Mt using a simple upscaling model based on the observations of CO2 flux during the field experiment.

Intercomparison of five PM10 monitoring devices and the implications for exposure measurement in epidemiological research

Five different instruments for the determination of the mass concentration of PM10 in air were compared side-by-side for up to 33 days in an undisturbed indoor environment: a tripod mounted BGI Inc. PQ100 gravimetric sampler with a US EPA certified Graseby Andersen PM10 inlet; an Airmetrics Minivol static gravimetric sampler; a Casella cyclone gravimetric personal sampler; an Institute of Occupational Medicine gravimetric PM10 personal sampler; and two TSI Inc. Dustrak real-time optical scattering personal samplers. For 24 h sampling of ambient PM10 concentrations around 10 microg m(-3), the estimated measurement uncertainty for the two gravimetric personal samplers was larger (approximately +/- 20%) compared with estimated measurement uncertainty for the PQ100/Graseby Andersen sampler (< +/- 5%). Measurement uncertainty for the Dustraks was lower (approximately +/- 15% on average) but calibration of the optical response against a reference PM10 method is essential since the Dustraks systematically over-read PM10 determined gravimetrically by a factor approximately 2.2. However, once calibrated, the Dustrak devices demonstrated excellent functionality in terms of ease of portability and real-time data acquisition. Estimated measurement uncertainty for PM10 concentrations determined with the Minivol were +/- 5%. The Minivol data correlated well with PQ100/Graseby Andersen data (r= 0.97, n = 18) but were, on average, 23% greater. The reason for the systematic discrepancy could not be traced. Intercomparison experiments such as these are essential for assessing measurement error and revealing systematic bias. Application of two Dustraks demonstrated the spatial and temporal variability of exposure to PM10 in different walking and transport microenvironments in the city of Edinburgh, UK. For example, very large exposures to PM10 were identified for the lower deck of a double-decker tour bus compared with the open upper deck of the same vehicle. The variability observed emphasises the need to determine truly personal exposure profiles of PM10 for quantifying exposure response relationships for epidemiological studies.