Isotopic approach for sources deconvolution of atmospheric NH4 NO3
Résumé
During events of particle pollution, especially at springtime, ammonium nitrate (NH4NO3) often displays the strongest increase in concentration, totaling almost half of the mass concentration of the particle mass load. This often leads to exceed the 50 μg m-3 daily threshold imposed by the European regulation on air quality to inform the public. The continental scale of such pollution events poses severe threat to human health and decreases significantly the quality of our environment. It is therefore the uppermost importance to identify the reason and sources leading to the formation of the ammonium nitrate particles. In this context, the INACS program was set up to investigate the potential of using the stable isotopes of nitrogen and oxygen to discriminate the factors responsible for the formation of NH4NO3 particles. The deconvolution of the potential sources of this particulate matter, a secondary particle species formed by the acid-base interaction between HNO3 and NH3, is particularly difficult to trace through "traditional" analytical chemistry methods. We used the well-established denitrifier bacteria method developed (eg. Kaiser et al., 2007 and references therein) to determine the nitrogen and triple oxygen isotopic composition of NO3 - (further details in Morin et al. 2008, 2009). For NH4 +, the azide method developed by Liu et al. (2014) is used to determine its nitrogen isotopic composition. Figure 1 shows the chemical pattern of two pollution events that occurred in 2013-2014. While the winter event can reasonably be attributed to the oil-fired and wood-burning heating applications, the springtime event shows a clearly different pattern with the majority of the increase of mass concentration due to the formation of ammonium nitrate...