Abstract
There is increasing awareness amongst the general public about exposure to atmospheric pollution while travelling in urban areas especially when taking active travelling modes such as walking and cycling. This study presents a comparative investigation of ultrafine particles (UFP), PM10, PM2.5, PM1 exposure levels associated with four transport modes (i.e., walking, cycling, car, and subway) in the city of Milan measured by means of portable instruments. Significant differences in particle exposure between transport modes were found. The subway mode was characterized by the highest PM mass concentrations: PM10, PM2.5, PM1 subway levels were respectively about 2-4-3 times higher than those of the car and open air active modes (i.e. cycling and walking). Conversely, these latter modes displayed the highest UFP levels about 2 to 3 times higher than the subway and car modes, highlighting the influence of direct traffic emissions. The car mode (closed windows, air conditioning and air recirculation on) reported the lowest PM and UFP concentration levels. In particular, the open-air/car average concentration ratio varied from about 2 for UFP up to 4 for PM1 and 6 for PM10 and PM2.5, showing differences that increase with increasing particle size. This work points out that active mode travelling in Milan city centre in summertime results in higher exposure levels than the car mode. Walkers’ and cyclists’ exposure levels is expected to be even higher during wintertime, due to the higher ambient PM and UFP concentration. Interventions intended to re-design the urban mobility should therefore include dedicated routes in order to limit their exposure to PM and UFP by increasing their distance from road traffic.
Highlights
Long-term exposure to fine particulate air pollution is associated with non-accidental cause mortality, even within concentration ranges well below the European annual mean limit value [1]
particle number concentration (PNC) levels measured for the open-air modes are in agreement with those reported for urban environments more or less directly influenced by traffic emissions [32,33]
Car levels in this study are significantly lower than the average PNCs reported in other European studies but they are in rather good agreement with those reported by Spinazzè et al (2015) [6] for car trips in Como, a mid-sized city 50 km North of Milan (0.9 ± 0.9 × 104 cm−3)
Summary
Long-term exposure to fine particulate air pollution is associated with non-accidental cause mortality, even within concentration ranges well below the European annual mean limit value [1]. Most of the documented associations were derived by time series analysis, relating day-to-day variation of air pollution and mortality and morbidity data [4]. In these analyses the population exposure to particles was usually assessed indirectly based on outdoor concentrations measured at fixed monitoring stations. Different studies have focused their attention on transport MEs directly measuring personal exposure to various size fractions of PM mass (PM10, PM2.5, PM1) and more recently to UFP number concentration by means of portable instruments. Karanasiou et al (2014) [7] reviewed several European studies on personal exposure during commuting by different modes of transports and suggested that the commuter exposure to traffic related pollutants (PM, black carbon, UFP in particular) may be potentially reduced by a forward-looking, integrated transport policy, involving the phased renovation of existing public vehicles and the withdrawal of the more polluting (older) private vehicles, combined with incentives to use public transport and the encouragement of commuter physical exercise
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