Ammonia (NH₃) is the main alkaline compound in the atmosphere, playing an important role in to neutralizing anthropogenic acidic emissions. Gaseous ammonia fosters undesirable consequences in aquatic and terrestrial ecosystems, including eutrophication. Agricultural activities have been considered as main ammonia emissions source, principally from NH₃-based fertilizer applications and animal husbandry. The incorporation of three-way catalytic converter technology in vehicles running with petrol has significantly increased non-agricultural ammonia emissions, especially in urban areas. Recent estimates indicate an increase of more than 200 times in vehicular nitrogen emissions in the form of ammonia since 1995. Considering the São Paulo, Brazil city vehicle fleet as a case study, this research aims to characterize the temporal patterns associated with urban ammonia. The environmental agency of São Paulo (CETESB) reports that from the total vehicle fleet of over 7 million vehicles, 46% of vehicles since 1999 are equipped with three-way catalysts.
This study evaluated ammonia concentration variability at a street with heavy traffic in a São Paulo summer season from November 9 to December 17, 2013. Ammonia concentrations were measured by a Picarro G2103 continuous monitor (3s time resolution). The hourly NH₃ concentrations showed a relationship with traffic, presenting maximum values between 8 a.m. to 10 a.m. During the monitoring period, lower NH3 concentrations were observed on weekends, mainly on Sundays. The average ammonia values were 11 ppb (8 μg m-3), reaching maximum values of 30 ppb (22 μg m-3). These concentrations were higher than some agricultural areas, and comparable to the levels in urban areas of Europe and USA.