Summer ammonia measurements in a densely populated Mediterranean city
Real-time measurements of ambient concentrations of gas-phase ammonia (NH sub(3)) were performed in Barcelona (NE Spain) in summer between May and September 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 NH sub(3) were higher at CC (5.6 plus or minus 2.1 mu g m super(-3) or 7.5 plus or minus 2.8 ppbv) compared with UB (2.2 plus or minus 1.0 mu g m super(-3) or 2.9 plus or minus 1.3 ppbv). This difference is attributed to the contribution from non-traffic sources such as waste containers, sewage systems, humans and open markets more dense in the densely populated historical city centre. Under high temperatures in summer these sources had the potential to increase the ambient levels of NH sub(3) well above the urban-background-traffic-influenced UB measurement station. Measurements were used to assess major local emissions, sinks and diurnal evolution of NH sub(3). The measured levels of NH sub(3), especially high in the old city, may contribute to the high mean annual concentrations of secondary sulfate and nitrate measured in Barcelona compared with other cities in Spain affected by high traffic intensity. Ancillary measurements, including PM sub(10), PM sub(2.5), PM sub(1) levels (Particulate Matter with aerodynamic diameter smaller than 10 mu m, 2.5 mu m, and 1 mu m), gases and black carbon concentrations and meteorological data, were performed during the measurement campaign. The analysis of specific periods (3 special cases) during the campaign revealed that road traffic was a significant source of NH sub(3). However, its effect was more evident at UB compared with CC where it was masked given the high levels of NH sub(3) from non-traffic sources measured in the old city. The relationship between SO sub(4) super(2-) daily concentrations and gas-fraction ammonia (NH sub(3)/(NH sub(3) + NH sub(4) super(+))) revealed that the gas-to-particle phase partitioning (volatilization or ammonium salts formation) also played an important role in the evolution of NH sub(3) concentration in summer in Barcelona.