Atmospheric ammonia in a changing climate: seven years of variability, drivers, and implications for the Po valley (2017–2024)

Atmospheric ammonia (NH₃) has received increasing attention in air quality research because of its role in the formation of secondary particulate matter and its influence on atmospheric chemistry. In many regions, agriculture represents the main source of NH₃ emissions, making it important to understand how ammonia concentrations vary over time. This thesis investigates the temporal variability and statistical characteristics of atmospheric ammonia measured at the San Pietro Capofiume monitoring station (44°39′N, 11°37′E) in the Po Valley, one of the most intensive agricultural areas in Europe. The analysis is based on hourly NH₃ observations collected between July 2017 and May 2024 together with meteorological data provided by Arpae Emilia-Romagna. A time series analysis was first carried out to identify seasonal and annual patterns in ammonia concentrations. Peak events were then examined in relation to meteorological conditions using statistical tests including the Shapiro Wilk test and the Mann Whitney U test. Particular attention was given to the unusually high concentrations observed in 2018. The results indicate that these peaks were mainly related to the so called March Barrier phenomenon. Excessive spring precipitation caused soil saturation and delayed fertilization activities, which compressed the nitrogen application period. When fertilization resumed, a heatwave in May characterized by high temperatures and low relative humidity created favorable conditions for rapid ammonia volatilization. Overall, the results show that the interaction between agricultural practices and meteorological variability can strongly influence ammonia emissions and contribute to pollution episodes in the Po Valley.