Abstract
Abstract. Real-time measurements of ambient concentrations of gas-phase ammonia (NH3) 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 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 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 NH3 well above the urban-background-traffic-influenced UB measurement station. Measurements were used to assess major local emissions, sinks and diurnal evolution of NH3. The measured levels of NH3, 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 PM10, PM2.5, PM1 levels (Particulate Matter with aerodynamic diameter smaller than 10 μm, 2.5 μm, and 1 μm), 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 NH3. However, its effect was more evident at UB compared with CC where it was masked given the high levels of NH3 from non-traffic sources measured in the old city. The relationship between SO42− daily concentrations and gas-fraction ammonia (NH3/(NH3 + NH4+)) revealed that the gas-to-particle phase partitioning (volatilization or ammonium salts formation) also played an important role in the evolution of NH3 concentration in summer in Barcelona.
Highlights
Atmospheric ammonia (NH3) is among the most abundant nitrogen compounds in the atmosphere and it plays an important role in the neutralization of atmospheric acids to form ammonium salts, preferentially ammonium sulfate ((NH4)2SO4) and ammonium bisulfate (NH4HSO4) from sulfuric acid
In this study we present the results of a measurement campaign performed in Barcelona (NE Spain) between May and September 2011 and mainly aimed: (a) to study the differences in the concentrations and dynamics of ambient NH3 at two urban sites with different characteristics in term of NH3 emission sources; (b) to asses major sources and sinks affecting the daily evolution of NH3 concentrations; (c) to understand the reasons for the high concentrations of secondary sulfate particles usually observed in Barcelona in summer compared with other urban and industrial sites across Spain (Querol et al, 2008)
The two AiRRmonia instruments deployed at urban background traffic-influenced area (UB) and city centre (CC) sites were intercompared before the measurement campaign in order to assure the quality of the intercomparison between the NH3 concentrations measured at both measurement sites
Summary
Atmospheric ammonia (NH3) is among the most abundant nitrogen compounds in the atmosphere and it plays an important role in the neutralization of atmospheric acids to form ammonium salts, preferentially ammonium sulfate ((NH4)2SO4) and ammonium bisulfate (NH4HSO4) from sulfuric acid. Measurements of ambient NH3 concentrations at urban level have been recently presented in many publications (Nowak et al, 2002; Perrino et al, 2002; Bari et al, 2003; Lin et al, 2006; Edgerton et al, 2007; Saylor et al, 2010; Nowak et al, 2010; Ianniello et al, 2010; Meng et al, 2011; Gong et al, 2011, among others) These studies agreed with the fact that the concentrations and evolution of ambient NH3 at urban level were influenced by traffic emissions together with other important factors such as temperature changes (mainly seasonally), wind speed or direction, boundary layer deep and mixing, other local or regional NH3 emissions, dry deposition, and gas-to-particle partitioning. The differences in NH3 concentrations and daily evolutions at the two selected sites in Barcelona (one in the historical city centre and one in a traffic-influenced urban background area) will be presented and discussed
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