76 Investigation of the correlation between various air pollution metrics and effects on asthma; a time series study in southern Sweden
研究了瑞典南部低污染水平下不同空气污染指标（如PM10、NO2等）与哮喘患者初级保健就诊的关系，发现即使污染浓度很低，也存在显著的健康风险，且不同指标的风险差异较大。
<h3>Introduction</h3> Different metrics of daily levels of particulate matter were used to study the association between air pollution and primary health care visits of asthma sufferers in an area with air pollution levels well within the standard air quality guidelines. <h3>Methods</h3> Hourly readings of ambient particulate matter (PM<sub>10</sub>, PM<sub>2.5</sub>), nitrogen dioxide (NO<sub>2</sub>), nitrogen oxide (NO), ozone (O<sub>3</sub>) and sulphur dioxide (SO<sub>2</sub>) from the Swedish Meteorological and Hydrological Institute (SMHI) from 2005 to 2010 were used. Six different metrics were created from these hourly readings: (1) daily 1-h maximum; (2) 24-h average; (3) commuting-period; (4) daytime average; (5) night-time average; and (6) the daily 8-h maximum. Outcome data were obtained from a regional health care database, covering approximately half a million people living in Malmö and neighbouring municipalities. Poisson generalised linear models were used to examine the relations between daily primary health care (PHC) visits due to asthma and air pollution metrics with different time lags. <h3>Results</h3> Air pollutant levels throughout the study period remained well within the WHO air quality guidelines (PM<sub>10</sub> daily mean of 16.4 μg/m<sup>3</sup>). A consistent relation between daily PM levels and PHC visits due to asthma was observed for all metrics. An increased risk of 11% was found with every 10-unit increase in daily mean levels of PM<sub>10</sub>. Commuting-period and daytime concentrations of PM<sub>10</sub> were also associated with increased risks, of 10% and 9%, respectively. The increased risk was moderate for the 8-hour (8%) and night-time (7%) metrics. The lowest risk was observed for the 1-hour maximum value (3%). <h3>Conclusions</h3> The results suggest that air pollution has adverse effects on respiratory health, even at very low concentrations. A significant variation in risk was observed during the day depending on the metric used. The results of this study highlight the need to re-assess air quality guidelines.