Atmospheric Chemistry and Physics Summer ammonia measurements in a densely populated Mediterranean city

Abstract. Real-time measurements of ambient concentra-tions of gas-phase ammonia (NH3) were performed in Barcelona (NE Spain) in summer between May and Septem-ber 2011. Two measurement sites were selected: one in an urban background traffic-influenced area (UB) and the other in the historical city centre (CC). Levels of NH3 were higher at CC (5.6 ± 2.1 µg m−3 or 7.5 ± 2.8 ppbv) compared with UB (2.2 ± 1.0 µg m−3 or 2.9 ± 1.3 ppbv). This difference is attributed to the contribution from non-traffic sources such as waste containers, sewage systems, humans and open mar-kets more dense in the densely populated historical city cen-tre. Under high temperatures in summer these sources had the potential to increase the ambient levels of NH3 well above the urban-background-traffic-influenced UB measure-ment station. Measurements were used to assess major loca