Methodology for setup and data processing of mobile air quality measurements to assess the spatial variability of concentrations in urban environments Martine Van Poppel * , Jan Peters, Nico Bleux VITO e Flemish Institute for Technological Research, Boeretang 200, 2400 Mol, Belgium article info Article history: Received 29 August 2012 Received in revised form 29 December 2012 Accepted 19 February 2013 Keywords: Air quality monitoring Mobile measurements Fixed monitoring Ultrafine particles Black carbon Background correction PM 2.5 abstract A case study is presented to illustrate a methodology for mobile monitoring in urban environments. A dataset of UFP, PM 2.5 and BC concentrations was collected. We showed that repeated mobile measure- ments could give insight in spatial variability of pollutants at different micro-environments in a city. Streets of contrasting traffic intensity showed increased concentrations by a factor 2e3 for UFP and BC and by <10% for PM 2.5 . The first quartile (P25) of the mobile measurements at an urban background zone seems to be good estimate of the urban background concentration. The local component of the pollutant concentrations was determined by background correction. The use of background correction reduced the number of runs needed to obtain representative results. The results presented, are a first attempt to establish a methodology for setup and data processing of mobile air quality measurements to assess the spatial variability of concentrations in urban environments. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Traffic-related air pollution is one of the major concerns in urban environments. Fixed air quality monitoring stations have several limitations when used to assess people’s real life exposure to (ultra)fine particles and other traffic-related air pollutants, due to the large spatial variability of these pollutants in urban envi- ronments. Mobile platforms are increasingly used to acquire air quality data at a high spatial and temporal resolution in a complex urban environment (e.g. Adams et al., 2012; Hagler et al., 2010; Wallace et al., 2009; Westerdahl et al., 2005; Weijers et al., 2004). Mobile measurements provide a solution to assess spatial vari- ability of pollutants with a limited number of instruments and in a confined timeframe. Typically, measurements are performed in the area of interest by repeated runs (Peters et al., 2013). In this paper the term ‘run(s)’ is used to specify repeated measurements over the entire area at different days and/or different times of one day. In this way, mobile measurements can be used for air quality mapping, hot spot identification and exposure assessment. How- ever, issues related to the data coverage requirements of mobile runs and to the variation in background concentrations are not yet solved. Air pollutant concentrations contain a regional and an urban background component in addition to the street level component. The urban background component is the contribution to the measured concentration at street level, not coming from local sources in the street but originating from regional and urban sources. Temporal variations in the background concentration may mask the contribution of local sources to the air quality, and complicate the comparison of the air quality between measure- ments of different dates. The air quality measured on a day with a high background concentration at a street with low traffic intensity can exceed the concentration measured at a location with many local sources when background concentrations are low. Therefore, background concentrations need to be taken into account when comparing measurements on different days, especially in order to assess the local source contribution. Local contributions (from traffic) to air pollutants can be calculated by subtracting the measured concentration at an urban background station from the concentration measured at a kerbside station (Lenschow et al., 2001). Also distance to the traffic source affects the resulting concentration (Mishra et al., 2012). This study focuses on mobile monitoring of the ultrafine parti- cles (UFP), PM 2.5 and black carbon (BC) in urban environments. * Corresponding author. E-mail address: martine.vanpoppel@vito.be (M. Van Poppel). Contents lists available at SciVerse ScienceDirect Environmental Pollution journal homepage: www.elsevier.com/locate/envpol 0269-7491/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.envpol.2013.02.020 Environmental Pollution 183 (2013) 224e233