Locations of the Kallio and Vallila air quality stations in Helsinki. The Vallila station is located in urban traffic (UT) environment and the Kallio station is located in urban background (UB) environment(adapted from [47]).

<p>Locations of the Kallio and Vallila air quality stations in Helsinki. The Vallila station is located in urban traffic (UT) environment and the Kallio station is located in urban background (UB) environment(adapted from [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0138507#pone.0138507.ref047" target="_blank">47</a>]).</p>