Personal exposure to black carbon in Stockholm, using different intra-urban transport modes

Merritt, A.S.; Georgellis, A.; Andersson, N.; Bedada, G.B.; Bellander, T.; Johansson, C.
2019 | Sci. Total Environ.

The traffic microenvironment has been shown to be a major contributor to the total personal exposure of black carbon (BC), and is key to local actions aiming at reducing health risks associated with such exposure. The main aim of the study was to get a better understanding of the determinants of traffic-related personal exposure to BC in an urban environment.

Personal exposure to ambient levels of BC was monitored while walking, cycling and traveling by bus or car along four streets and while cycling alternative routes simultaneously. Monitoring was performed during morning and afternoon peak hours and at midday, with a portable aethalometer recording one-minute mean values. In all, >4000 unique travel passages were performed. Stepwise Linear Regression was used to assess predictors to personal exposure levels of BC.

The personal BC concentration ranged 0.03–37 μg/m3. The average concentrations were lowest while walking (1.7 μg/m3) and highest traveling by bus (2.7 μg/m3). However, only 22% of the variability could be explained by travel mode, urban background BC and wind speed. BC concentrations measured inside a car were on average 33% lower than measured simultaneously outside the car. Choosing an alternative bicycle route with less traffic resulted in up to 1.4 μg/m3 lower personal exposure concentrations.

In conclusion, traveling by bus rendered the highest personal BC concentrations. But when taking travel time and inhalation rate into account, the travel-related exposure dose was predicted to be highest during walking and cycling. It is however probable that the benefits from physical activity outweigh health risks associated with this higher exposure dose.

It is clear that road traffic makes an important contribution to personal exposure to BC regardless of mode of intra-urban transport. Our data suggest that commuting along routes with lower BC levels would substantially decrease commuter's exposure.

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.

Road dust load dynamics and influencing factors for six winter seasons in Stockholm, Sweden

Gustafsson, M.; Blomqvist, G.; Järlskog, I; Lundberg, J.; Janhäll, S.; Elmgren, M.; Johansson, C.; Norman, M.; Silvergren, S.
2019 | Atmos Environ

Traffic related non-exhaust particulate sources and road dust are an increasingly important source for PM10 air pollution as exhaust sources are decreasing due to regulations. In the Nordic countries, the road dust problem is enhanced by use of studded tyres, causing increased road wear and winter road maintenance including gritting. Efforts to reduce road dust emissions requires knowledge on temporal and spatial road dust load dynamics. The city of Stockholm, Sweden, has therefore financed seasonal (October to May) road dust sampling to be able to optimize their winter and spring time street operation measures for reduced road dust emissions. This work describes the outcome of six seasons (2011/2012 – 2016/2017) of road dust sampling in five central streets using the VTI wet dust sampler (WDS).The results show that road dust load, expressed as DL180 (dust load smaller than 180 μm) has a seasonal variation with the highest loads (up to 200 g/m2) in late winter and early spring and a minimum (down to about 15 g/m2) in early autumn and late spring. The dust load varies between streets and is depending on pavement surface properties. On a smaller scale the dust load has a high variability across streets due to differences in rates of suspension from different parts of the road surface, with low amounts in wheel tracks and higher in-between and outside the tracks. Between 2–30% of the DL180 is smaller than 10 μm and could directly contribute to PM10 emissions. In general, higher road surface texture leads to higher dust loads, but the condition of the pavement (e.g. cracks, aggregate loss) might also have an effect. A new, wear resistant pavement accumulated markedly higher road dust amounts than a several years old pavement. This paper closes with a discussion on the complex relation between road dust load and PM10 concentrations and a discussion on the challenges and comparability of road dust sampling techniques and measures.

Trends in MODIS and AERONET derived aerosol optical thickness over Northern Europe.

2019 | Tellus B Chem Phys Meteorol | 71 (1) (1-21)

Long-term Aqua and Terra MODIS (MODerate resolution Imaging Spectroradiometer) Collections 5.1 and 6.1 (c051 and c061, respectively) aerosol data have been combined with AERONET (AERosol RObotic NETwork) ground-based sun photometer observations to examine trends in aerosol optical thickness (AOT, at 550 nm) over Northern Europe for the months April to September. For the 1927 and 1559 daily coincident measurements that were obtained for c051 and c061, respectively, MODIS AOT varied by 86 and 90%, respectively, within the predicted uncertainty of one standard deviation of the retrieval over land (ΔAOT = ±0.05 ± 0.15·AOT). For the coastal AERONET site Gustav Dalen Tower (GDT), Sweden, larger deviations were found for MODIS c051 and c061 (79% and 75%, respectively, within predicted uncertainty). The Baltic Sea provides substantially better statistical representation of AOT than the surrounding land areas and therefore favours the investigations of trends in AOT over the region. Negative trends of 1.5% and 1.2% per year in AOT, based on daily averaging, were found for the southwestern Baltic Sea from MODIS c051 and c061, respectively. This is in line with a decrease of 1.2% per year in AOT at the AERONET station Hamburg. For the western Gotland Basin area, Sweden, negative trends of 1.5%, 1.1% and 1.6% per year in AOT have been found for MODIS c051, MODIS c061 and AERONET GDT, respectively. The strongest trend of –1.8% per year in AOT was found for AERONET Belsk, Poland, which can be compared to –1.5% per day obtained from MODIS c051 over central Poland. The trends in MODIS and AERONET AOT are nearly all statistically significant at the 95% confidence level. The strongest aerosol sources are suggested to be located southwest, south and southeast of the investigation area, although the highest prevalence of pollution events is associated with air mass transport from southwest.

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.

Air pollution as a risk factor in health impact assessments of a travel mode shift towards cycling

Raza, W.; Forsberg, B.; Johansson, C.; Nilsson Sommar, J.
2018 | Glob Health Action | 11 (1)

Air pollution as a risk factor in Health Impact Assessments of increased cycling
There is growing evidence that promotion of active commuting provide substantial health and environmental benefits by influencing air pollution, physical activity, accidents and noise. However, studies evaluating intervention and policies on mode shift from motorized transport to cycling have estimated impacts with varying validity and precision.
The purpose of this paper is to review and discuss estimation of air pollution exposure and its impact on in health impact assessment studies of shift from car driving to bicycling and to guide future assessments.
A systematic database search of PubMed and Google scholar was done from January 2000 to May 2016 according to PRISMA guidelines.
We identified 18 health impact assessment studies of mode shift that evaluated air pollution effects. Most of these studies investigated future hypothetic scenarios of increased cycling. Almost all used different emission predictive models for the estimation of reduced emission due to decreased car usage. The impact on general population was estimated using a comparative risk assessment approach in the majority of these studies whereas some used previous published cost estimates without considering any dose-response functions. Air pollution exposure during cycling was estimated based on the ventilation rate during cycling, pollutant concentration and trip duration. Most studies employed exposure response functions from studies comparing the background air pollution levels between cities to estimate the health impacts of local traffic emission. Effects of increased cycling contributed small health benefits for the general population but slightly increased risks associated with pollution exposure among those that shifted to cycling.
A large discrepancy between studies was observed due to, different health impact assessment approaches, different assumptions when creating scenarios, assumption for calculating inhaled dose, dose- response functions and availability of data. More research is required to address these methodological issues.

On particulate emissions from moving trains in a tunnel environment

Chaa, Y.; Olofsson, U.; Gustafsson, M.; Johansson, C.
2018 | Transportation Research Part D: Transport and Environment | 59 (35-45)

Increasing attention is being paid to airborne particles in railway environments because of their potential to adversely affect health. In this study, we investigate the contribution of moving trains to both the concentration and size distribution of particles in tunnel environments. Real-time measurements were taken with high time-resolution instruments at a railway station platform in a tunnel in Stockholm in January 2013. The results show that individual trains stopping and starting at the platform substantially elevate the particulate concentrations with a mobility diameter greater than 100 nm. Two size modes of the particulate number concentrations were obtained. A mode of around 170 nm occurs when a train moves, while the other mode peaks at about 30 nm when there is no train in the station. By using principal component analysis (PCA), three contributing sources were identified on the basis of the classification of the sizes of the particles, namely railway-related mechanical wear, suspension due to the movement of trains and sparking of electric-powered components. It is concluded that the particulate matter released by individual moving trains is a key contributor to fine particles (100–500 nm) on the railway platform in a tunnel.

Trends in black carbon and size-resolved particle number concentrations and vehicle emission factors under real-world conditions

Krecl, P.; Johansson, C.; Targino, A.C.; Ström, J.; Burman, L.
2017 | Atmos Environ | 165 (155-168)

Kerbside concentrations of NOx, black carbon (BC), total number of particles (diameter > 4 nm) and number size distribution (28–410 nm) were measured at a busy street canyon in Stockholm in 2006 and 2013. Over this period, there was an important change in the vehicle fleet due to a strong dieselisation process of light-duty vehicles and technological improvement of vehicle engines. This study assesses the impact of these changes on ambient concentrations and particle emission factors (EF). EF were calculated by using a novel approach which combines the NOx tracer method with positive matrix factorisation (PMF) applied to particle number size distributions. NOx concentrations remained rather constant between these two years, whereas a large decrease in particle concentrations was observed, being on average 60% for BC, 50% for total particle number, and 53% for particles in the range 28–100 nm. The PMF analysis yielded three factors that were identified as contributions from gasoline vehicles, diesel fleet, and urban background. This separation allowed the calculation of the average vehicle EF for each particle metric per fuel type. In general, gasoline EF were lower than diesel EF, and EF for 2013 were lower than the ones derived for 2006. The EFBC decreased 77% for both gasoline and diesel fleets, whereas the particle number EF reduction was higher for the gasoline (79%) than for the diesel (37%) fleet. Our EF are consistent with results from other on-road studies, which reinforces that the proposed methodology is suitable for EF determination and to assess the effectiveness of policies implemented to reduce vehicle exhaust emissions. However, our EF are much higher than EF simulated with traffic emission models (HBEFA and COPERT) that are based on dynamometer measurements, except for EFBC for diesel vehicles. This finding suggests that the EF from the two leading models in Europe should be revised for BC (gasoline vehicles) and particle number (all vehicles), since they are used to compile national inventories for the road transportation sector and also to assess their associated health effects. Using the calculated kerbside EF, we estimated that the traffic emissions were lower in 2013 compared to 2006 with a 61% reduction for BC (due to decreases in both gasoline and diesel emissions), and 34–45% for particle number (reduction only in gasoline emissions). Limitations of the application of these EF to other studies are also discussed.

Health Impact of PM10, PM2.5 and Black Carbon Exposure Due to Different Source Sectors in Stockholm, Gothenburg and Umea, Sweden.

Segersson, D.; Eneroth, K.; Gidhagen, L.; Johansson, C.; Omstedt, G.; Nylén A.E.; Forsberg, B.
2017 | Int J Environ Res Public Health | 14 (7)

The most important anthropogenic sources of primary particulate matter (PM) in ambient air in Europe are exhaust and non-exhaust emissions from road traffic and combustion of solid biomass. There is convincing evidence that PM, almost regardless of source, has detrimental health effects. An important issue in health impact assessments is what metric, indicator and exposure-response function to use for different types of PM. The aim of this study is to describe sectorial contributions to PM exposure and related premature mortality for three Swedish cities: Gothenburg, Stockholm and Umea. Exposure is calculated with high spatial resolution using atmospheric dispersion models. Attributed premature mortality is calculated separately for the main local sources and the contribution from long-range transport (LRT), applying different relative risks. In general, the main part of the exposure is due to LRT, while for black carbon, the local sources are equally or more important. The major part of the premature deaths is in our assessment related to local emissions, with road traffic and residential wood combustion having the largest impact. This emphasizes the importance to resolve within-city concentration gradients when assessing exposure. It also implies that control actions on local PM emissions have a strong potential in abatement strategies.

Cancer Risk Assessment of Airborne PAHs Based on in Vitro Mixture Potency Factors

Dreij, K.; Mattsson, Å.; Jarvis, I.W.H.; Lim, H.; Hurkmans, J.; Gustafsson, J.; Bergvall, C.; Westerholm, R.; Johansson, C.; Stenius, U.
2017 | Environ. Sci. Technol. | 51 (8805-8814)

Complex mixtures of polycyclic aromatic
hydrocarbons (PAHs) are common environmental pollutants
associated with adverse human health effects including cancer.
However, the risk of exposure to mixtures is difficult to
estimate, and risk assessment by whole mixture potency
evaluations has been suggested. To facilitate this, reliable in
vitro based testing systems are necessary. Here, we investigated
if activation of DNA damage signaling in vitro could be an
endpoint for developing whole mixture potency factors
(MPFs) for airborne PAHs. Activation of DNA damage
signaling was assessed by phosphorylation of Chk1 and H2AX
using Western blotting. To validate the in vitro approach,
potency factors were determined for seven individual PAHs
which were in very good agreement with established potency factors based on cancer data in vivo. Applying the method using
Stockholm air PAH samples indicated MPFs with orders of magnitude higher carcinogenic potency than predicted by established
in vivo-based potency factors. Applying the MPFs in cancer risk assessment suggested that 45.4 (6% of all) lung cancer cases per year
in Stockholm are due to airborne PAHs. Applying established models resulted in <1 cancer case per year, which is far from expected levels. We conclude that our in vitro based approach for establishing MPFs could be a novel method to assess whole mixture samples of airborne PAHs to improve health risk assessment.

Driftåtgärder mot PM10 i Stockholm

Gustafsson, M.; Blomqvist, G.; Janhäll, S.; Johansson, C.; Järlskog, I.; Lundberg, J.; Norman, M.; Silvergren, S.
2017 | Väg- och transportforskningsinstitutet, VTI (VTI rapport 928) | Report No: 928

Since 2011, Stockholm has made special efforts to reduce PM10 levels in the city. The efforts mainly
include dust binding with CMA (calcium magnesium acetate) and vacuum suction with a powerful dry
vacuum suction machine. This report summarizes effects on particulate matter and road dust storage,
as the actions taken by Stockholm City during the 2015–2016 season and discusses how measures can
be further improved. The limit value for the environmental quality standard was not exceeded for the
2015–2016 season for the third consecutive year, but the number of days with PM10 levels over the
environmental quality standard was higher than in the previous season, which had a record low
number of exceedances. The evaluation of daytime dust binding was complicated by the fact that the
CMA was also used on the reference street, which caused to much uncertainties to provide quantitative
analysis of its effect this season. Block-wise dust binding and vacuuming could not be evaluated due
to dust contamination from a construction site. The dust load on the streets varies from a few g/m2
about 250 g/m2 depending on the street and season and is highest during the winter (Dec–Jan). A trend
towards lower dust loads is broken this season on several streets, which may be due to the damper
streets in spring. Analyses made on the connection between dust load, PM10 and impacting factors, as
well as a condition-based calculation method suggests that dust binding in spring is important for
keeping the levels down, while dust binding in autumn and winter is more often “unnecessary” (the
levels would probably not have exceeded the limit value also without dust binding).

Contact information

Visiting addresses:

Geovetenskapens Hus,
Svante Arrhenius väg 8, Stockholm

Arrheniuslaboratoriet, Svante Arrhenius väg 16, Stockholm (Unit for Analytical and Toxicological Chemistry)

Mailing address:
Department of Environmental Science and Analytical Chemistry (ACES)
Stockholm University
106 91 Stockholm

Press enquiries should be directed to:

Stella Papadopoulou
Science Communicator
Phone +46 (0)8 674 70 11