Association between Mortality and Short-Term Exposure to Particles, Ozone and Nitrogen Dioxide in Stockholm, Sweden

Olstrup, H.; Johansson, C.; Forsberg, B.; Åström, C.
2019 | Int J Environ Res Public Health | 16 (6) (1028-1042)

In this study, the effects on daily mortality in Stockholm associated with short-term exposure to ultrafine particles (measured as number of particles with a diameter larger than 4 nm, PNC4), black carbon (BC) and coarse particles (PM2.5–10) have been compared with the effects from more common traffic-pollution indicators (PM10, PM2.5 and NO2) and O3 during the period 2000–2016. Air pollution exposure was estimated from measurements at a 20 m high building in central Stockholm. The associations between daily mortality lagged up to two days (lag 02) and the different air pollutants were modelled by using Poisson regression. The pollutants with the strongest indications of an independent effect on daily mortality were O3, PM2.5–10 and PM10. In the single-pollutant model, an interquartile range (IQR) increase in O3 was associated with an increase in daily mortality of 2.0% (95% CI: 1.1–3.0) for lag 01 and 1.9% (95% CI: 1.0–2.9) for lag 02. An IQR increase in PM2.5–10 was associated with an increase in daily mortality of 0.8% (95% CI: 0.1–1.5) for lag 01 and 1.1% (95% CI: 0.4–1.8) for lag 02. PM10 was associated with a significant increase only at lag 02, with 0.8% (95% CI: 0.08–1.4) increase in daily mortality associated with an IQR increase in the concentration. NO2 exhibits negative associations with mortality. The significant excess risk associated with O3 remained significant in two-pollutant models after adjustments for PM2.5–10, BC and NO2. The significant excess risk associated with PM2.5–10 remained significant in a two-pollutant model after adjustment for NO2. The significantly negative associations for NO2 remained significant in two-pollutant models after adjustments for PM2.5–10, O3 and BC. A potential reason for these findings, where statistically significant excess risks were found for O3, PM2.5–10 and PM10, but not for NO2, PM2.5, PNC4 and BC, is behavioral factors that lead to misclassification in the exposure. The concentrations of O3 and PM2.5–10 are in general highest during sunny and dry days during the spring, when exposure to outdoor air tend to increase, while the opposite applies to NO2, PNC4 and BC, with the highest concentrations during the short winter days with cold weather, when people are less exposed to outdoor air.

A Multi-Pollutant Air Quality Health Index (AQHI) Based on Short-Term Respiratory Effects in Stockholm, Sweden

Olstrup, H.; Johansson, C.; Forsberg, B.; Tornevi, A.; Ekebom, A.; Meister, K.
2019 | Int J Environ Res Public Health | 16 (1) (105-129)

In this study, an Air Quality Health Index (AQHI) for Stockholm is introduced as a tool to capture the combined effects associated with multi-pollutant exposure. Public information regarding the expected health risks associated with current or forecasted concentrations of pollutants and pollen can be very useful for sensitive persons when planning their outdoor activities. For interventions, it can also be important to know the contribution from pollen and the specific air pollutants, judged to cause the risk. The AQHI is based on an epidemiological analysis of asthma emergency department visits (AEDV) and urban background concentrations of NOx, O3, PM10 and birch pollen in Stockholm during 2001–2005. This analysis showed per 10 µg·m–3 increase in the mean of same day and yesterday an increase in AEDV of 0.5% (95% CI: −1.2–2.2), 0.3% (95% CI: −1.4–2.0) and 2.5% (95% CI: 0.3–4.8) for NOx, O3 and PM10, respectively. For birch pollen, the AEDV increased with 0.26% (95% CI: 0.18–0.34) for 10 pollen grains·m–3. In comparison with the coefficients in a meta-analysis, the mean values of the coefficients obtained in Stockholm are smaller. The mean value of the risk increase associated with PM10 is somewhat smaller than the mean value of the meta-coefficient, while for O3, it is less than one fifth of the meta-coefficient. We have not found any meta-coefficient using NOx as an indicator of AEDV, but compared to the mean value associated with NO2, our value of NOx is less than half as large. The AQHI is expressed as the predicted percentage increase in AEDV without any threshold level. When comparing the relative contribution of each pollutant to the total AQHI, based on monthly averages concentrations during the period 2015–2017, there is a tangible pattern. The AQHI increase associated with NOx exhibits a relatively even distribution throughout the year, but with a clear decrease during the summer months due to less traffic. O3 contributes to an increase in AQHI during the spring. For PM10, there is a significant increase during early spring associated with increased suspension of road dust. For birch pollen, there is a remarkable peak during the late spring and early summer during the flowering period. Based on monthly averages, the total AQHI during 2015–2017 varies between 4 and 9%, but with a peak value of almost 16% during the birch pollen season in the spring 2016. Based on daily mean values, the most important risk contribution during the study period is from PM10 with 3.1%, followed by O3 with 2.0%.

Trends in air pollutants and health impacts in three Swedish cities over the past three decades

Olstrup, H.; Forsberg, B.; Orru, H.; Spanne, M.; Nguyen, H.; Molnár, P.; Johansson, C.
2018 | Atmos. Chem. Phys. Discuss.

Air pollution concentrations have been decreasing in many cities in the developed countries. We have estimated time trends and health effects associated with exposure to NOx, NO2, O3, and PM10 in the Swedish cities of Stockholm, Gothenburg, and Malmo from the 1990's to 2015. Trend analyses of concentrations have been performed by using the Mann-Kendall test and the Theil-Sen method. Measured concentrations are from central monitoring stations representing urban background levels, and they are assumed to indicate changes in long-term exposure to the population. However, corrections for population exposure have been performed for NOx, O3, and PM10 in Stockholm, and for NOx in Gothenburg. For NOx and PM10, the concentrations at the central monitoring stations are shown to overestimate exposure when compared to dispersion model calculations of spatially resolved population-weighted exposure concentrations, while the reverse applies to O3. The trends are very different for the pollutants that are studied; NOx and NO2 have been decreasing in all cities, O3 exhibits an increasing trend in all cities, and for PM10, there is a slowly decreasing trend in Stockholm, a slowly increasing trend in Gothenburg, and no significant trend in Malmo. When the trends are divided into weekdays and weekends, the decreasing trends associated with NOx and NO2 are more prominent during weekdays compared to weekends, indicating that local emission reductions from traffic to a large part have contributed to these declining trends.

Health effects in terms of changes in life expectancy are calculated based on the trends in exposure to NOx, NO2, O3, and PM10, and the relative risks associated with exposure to these pollutants. The decreased levels of NOx are estimated to increase the life expectancy by up to 11 months for Stockholm and 12 months for Gothenburg. This corresponds to up to one fifth of the total increase in life expectancy (54–70 months) in the cities during the period 1990–2015. In contrast to NOx and NO2, the changing trends associated with O3 and PM10 have relatively little impact on the change in life expectancy. NOx and NO2 are highly associated with vehicle exhaust emissions, indicating that decreasing road-traffic emissions have had significant impact on the public health in these cities.

The Use of Carbonaceous Particle Exposure Metrics in Health Impact Calculations

Olstrup, H.; Johansson, C.; Forsberg, B.
2016 | Int J Environ Res Public Health | 13 (249) (2-17)

Combustion-related carbonaceous particles seem to be a better indicator of adverse health
effects compared to PM2.5 and PM10. Historical studies are based on black smoke (BS), but more recent
studies use absorbance (Abs), black carbon (BC) or elemental carbon (EC) as exposure indicators. To
estimate health risks based on BS, we review the literature regarding the relationship between Abs,
BS, BC and EC. We also discuss the uncertainties associated with the comparison of relative risks
(RRs) based on these conversions. EC is reported to represent a proportion between 5.2% and 27% of
BS with a mean value of 12%. Correlations of different metrics at one particular site are higher than
when different sites are compared. Comparing all traffic, urban and rural sites, there is no systematic
site dependence, indicating that other properties of the particles or errors affect the measurements
and obscure the results. It is shown that the estimated daily mortality associated with short-term
levels of EC is in the same range as PM10, but this is highly dependent on the EC to BS relationship
that is used. RRs for all-cause mortality associated with short-term exposure to PM10 seem to be
higher at sites with higher EC concentrations, but more data are needed to verify this.

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