Assessing the ammonium nitrate formation regime in the Paris megacity and its representation in the CHIMERE model

Abstract

Abstract. Secondary inorganic compounds represent a major fraction of fine aerosol in the Paris megacity. The thermodynamics behind their formation is now relatively well constrained but, due to sparse direct measurements of their precursors (in particular NH3 and HNO3), uncertainties remain on their concentrations and variability as well as the formation regime of ammonium nitrate (in terms of limited species among NH3 and HNO3) in urban environments such as Paris. This study presents the first urban background measurements of both inorganic aerosol compounds and their gaseous precursors during several months within the city of Paris. Intense agriculture-related NH3 episodes are observed in spring/summer while HNO3 concentrations remain relatively low, even during summer, which leads to a NH3-rich regime in Paris. The local formation of ammonium nitrate within the city appears low, despite high NOx emissions. The data set also allows evaluating the CHIMERE chemistry-transport model (CTM). Interestingly, the rather good results obtained on ammonium nitrates hide significant errors on gaseous precursors (e.g., mean bias of −75 and +195 % for NH3 and HNO3, respectively). This leads to a misrepresentation of the nitrate formation regime through a highly underestimated gas ratio metric (introduced by Ansari and Pandis, 1998) and a much higher sensitivity of nitrate concentrations to ammonia changes. Several uncertainty sources are investigated, pointing out the importance of better assessing both NH3 agricultural emissions and OH concentrations in the future. These results remind us of the caution required when using of CTMs for emission scenario analysis, highlighting the importance of prior diagnostic and dynamic evaluations.

Elucidating the molecular mechanisms of Criegee-amine chemistry in the gas phase and aqueous surface environments

“…[22][23][24][25][26] Our results may help in better understanding the aerosol formation in the fog waters of California's central valley, and in polluted urban environments such as New York and Paris where signicant nitric acidamine chemistries have been recently suggested to play a role in the aerosol particle formation in these areas. [71][72][73] In the New York City area, amines are likely emitted from marine sources whereas in Paris, the source of amines is the agricultural activities around the City area. The intense traffic in these urban regions further support the role of the Criegee-amine interactions in the particle formation.…”

Solid Ammonium Nitrate Aerosols as Efficient Ice Nucleating Particles at Cirrus Temperatures

“…Ammonium nitrate (NH 4 NO 3 , AN) particles represent an important type of the anthropogenic aerosol (Bian et al, 2017; Drugé et al, 2019; Petetin et al, 2016; Tao et al, 2017; Y. Wang et al, 2013; Xu & Penner, 2012). Particulate AN is generated by the reaction between gaseous ammonia (NH 3 ) and nitric acid (HNO 3 ), the latter being formed by the oxidation of NO x species, that is, nitric oxide (NO) and nitric dioxide (NO 2 ) (Nowak et al, 2010; Paulot et al, 2016).…”

Two years of online measurement of fine particulate nitrate in the western Yangtze River Delta: influences of thermodynamics and N<sub>2</sub>O<sub>5</sub> hydrolysis

“…The gas-phase reaction of NO 2 and OH radicals is one major pathway to form nitric acid (HNO 3 ) (Calvert and Stockwell, 1983), which subsequently reacts with ammonia (NH 3 ) to produce ammonium nitrate (NH 4 NO 3 ). As typical photochemical processes, these reactions dominate daytime nitrate formation, and have been widely investigated in both field and modeling studies (Sharma et al, 2007;Petetin et al, 2016). Heterogeneous uptake of the photochemical formed nitric acid by alkali compounds, e.g., dust and sea salt particles, is also a considerable pathway to form nitrate in some regions (Bian et al, 2014).…”