Article pubs.acs.org/est
Redistribution of Traffic Related Air Pollution Associated with a New Road Tunnel Christine T. Cowie,*,†,‡ Nectarios Rose,†,§ Robert Gillett,∥ Scott Walter,†,§ and Guy B. Marks† †
Woolcock Institute of Medical Research, Sydney, NSW, Australia Cooperative Research Centre for Asthma and Airways, Sydney, Australia § NSW Health Department, Sydney, NSW, Australia ∥ CSIRO, Marine & Atmospheric Research, Melbourne, Australia ‡
S Supporting Information *
ABSTRACT: The aim of this study was to assess the effect of a new road tunnel on the concentration and distribution of traffic-related air pollution (TRAP), specifically nitrogen dioxide (NO2) and particulate matter (PM), and to determine its relationship to change in traffic flow. We used continuously recorded data from four monitoring stations at nonroadside locations within the study area and three regional monitors outside the area. The four monitors in the study area were in background locations where smaller pollutant changes were expected compared with changes near the bypassed main road. We also deployed passive samplers to assess finer spatial variability in NO2 including application of a land use regression model (LUR). The study was conducted from 2006 to 2008. Analysis of the continuously recorded data showed that the tunnel intervention did not lead to consistent reductions in NO2 or PM over the wider study area. However, there were significant decreases in NO2, NOx, and PM10 in the eastern section of the study area. Analysis of passive sampler data indicated that the greatest reductions in NO2 concentrations occurred within 100 m of the bypassed main road. The LUR model also demonstrated that changes in NO2 were most marked adjacent to the bypassed main road. These findings support the use of methods that highlight fine spatial variability in TRAP and demonstrate the utility of traffic interventions in reducing air pollution exposures for populations living close to main roads.
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INTRODUCTION Exposure to traffic-related air pollution (TRAP) has been associated with increased morbidity and mortality. Health effects including wheeze, cough, sputum production, other asthmarelated symptoms,1−7 impaired lung function,8,9 increased heart rate variability,5,10 and increased mortality11,12 have been reported. Recently there have been reports of lower birth weight in the offspring of mothers heavily exposed to TRAP.13,14 With increased recognition of the adverse health effects of TRAP, governments have sought to reduce the impact of vehicular emissions both by reducing emissions from the vehicle fleet15,16 and by reducing traffic. Policies to reduce traffic congestion have focused on introducing road use charges, for example, tolls, fees for use, and congestion charging zones, or limiting or excluding car use on specific days within city centers.17−20 Other TRAP reduction interventions have included lowering speed limits along certain sections of roads,21,22 implementation of temporary road closures due to major events,23,24 and a drastic reduction in traffic activity during military conflict.25 One of the most radical trafficrelated interventions occurred during the 2008 Beijing Olympics, where several air pollution reduction measures were instituted, including tightening of fuel standards for light duty as well as heavy diesel vehicles, banning the worst © 2012 American Chemical Society
polluting trucks from the city, incorporating odd and even number plate days for cars, and removing 70% of government-operated vehicles from the city.26 Additional opportunities for improving ambient air quality can arise on a sporadic basis when individual construction projects or other planning interventions result in localized traffic changes that have the effect of diverting traffic away from population centers27,28 or using tunnels to redirect traffic away from surface roads.29 Studies of the impact of these interventions have generally found a reduction in measured or modeled air pollutants after the intervention, although the reductions have sometimes been modest.18,27 The above interventions tend to fall into two categories. The first of these are interventions applied on a large geographic scale, such as whole cities or large areas within cities, for example, the Beijing Olympics26 and the London Congestion Charge;18 the second type applies to interventions that are much smaller in scale, for instance, traffic diversions or speed limit reductions.21,22 Given the contribution of regional, local and neighborhood Received: Revised: Accepted: Published: 2918
August 3, 2011 January 4, 2012 January 30, 2012 January 30, 2012 dx.doi.org/10.1021/es202686r | Environ. Sci. Technol. 2012, 46, 2918−2927
Environmental Science & Technology
Article
Figure 1. Study area showing the study boundary, tunnel route, fixed site monitors, and passive samplers.
March 2008 and resulted in three lanes of traffic in each direction being reduced to one general traffic lane as well as one dedicated bus lane in each direction and a cycle path (one lane). Air modeling conducted in the tunnel planning stage predicted relatively small local changes in air quality in two key subareas by 2016 modeled on traffic flows of 100 000 vehicles per day (vpd) in the tunnel on opening. These were (a) an area along and close to the main surface road bypassed by the road tunnel (predicted to experience up to a 40% decrease in NO2 and 5% decrease in PM10) and (b) two areas near the feeder roads to the tunnel (predicted to experience an increase of up to 10% in NO2 and 2% increase in PM10).33 Our hypothesis was that there would be a redistribution of TRAP within the area surrounding the road tunnel and the bypassed main road. Our aim was to test this hypothesis and to quantify the change in concentration and distribution of pollutants.
effects to overall air quality for any given location, interventions implemented over a large geographic area are likely to result in wider measurable impacts to air pollution throughout the urban area. In contrast, the impacts of smaller scale traffic interventions can only have a local effect. Given the steep gradient in air pollutant concentrations from heavily trafficked roads,30,31 the effect of these local interventions might be expected to be limited to within a few hundred meters of the intervention site. The opening of a road traffic tunnel in Sydney, NSW, Australia, in March 2007 presented the opportunity to study the effect of a local traffic intervention on air quality in the vicinity of the tunnel and the bypassed main road. The Lane Cove Tunnel (LCT) is a 3.6 km single carriageway road vehicular tunnel that links two major motorways and was the final segment of road infrastructure to complete the Sydney orbital road network. It is vented by two ventilation stacks, 134 and 62 m in height, respectively, and located at each end of the tunnel within light industrial estates.32 Apart from linking the two motorways, the tunnel was designed to divert traffic from a major surface road in the local area, thereby reinstating community amenity by reducing traffic congestion. The tunnel was opened to traffic on March 25, 2007. Concomitant major road changes made to the main surface road were introduced in
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MATERIALS AND METHODS Study Area. We defined the Lane Cove Tunnel (LCT) study area as an approximately 5 × 10 km area, incorporating motorways and other major and local roads. The area is predominantly residential, with pockets of parkland and 2919
dx.doi.org/10.1021/es202686r | Environ. Sci. Technol. 2012, 46, 2918−2927
Environmental Science & Technology
Article
conditions by including as covariates daily changes in temperature, wind direction weighted by speed, and wind speed. We additionally adjusted for changes in regional air quality, as measured at the DECCW sites, by including as another covariate the change in average daily readings from the DECCW sites combined (mean of the daily averages). We tested up to 20 lags, and used 0.05 as the significance cutoff. Residuals were plotted to check for normality, and the autocorrelation function (ACF) and partial autocorrelation function (PACF) were checked for each resulting model to confirm there was no autocorrelation in the residuals. These models were implemented in SAS 9.2 using the AUTOREG procedure. Passive Sampler Measurements. To characterize the spatial variability in TRAP, we measured nitrogen dioxide (NO2) using passive diffusion samplers placed simultaneously at 41 sites across the study area. We used NO2 as a marker of TRAP, as this pollutant displays small scale variation strongly associated with traffic.30,36,37 The measurement sites were chosen to maximize the observed cross-sectional variation in land use and traffic conditions. Hence, samplers were placed at sites ranging from the busiest roads to quiet background locations with very little traffic flow (e.g.,
