NH3 spatio-temporal variability over Paris, Mexico and Toronto and its link to PM2.5 during pollution events

<p>Large cities can experience high levels of fine particulate matter (PM_2.5) pollution linked to ammonia (NH₃) mainly emitted from agricultural activities. Using a combination of PM_2.5 and NH₃ measurements from in situ instruments, satellite infrared spectrometers, and atmospheric model simulations, we demonstrate the role of atmospheric NH₃ and meteorological conditions in pollution events occurring in Paris, Toronto, and Mexico City.</p> <p>Ten years of measurements from the Infrared Atmospheric Sounding Interferometer (IASI) are used to assess the spatio-temporal NH₃ variability over and around the three cities. The three regions are subject to long range transport of NH₃, as shown using HYSPLIT cluster back-trajectories. The results show that the NH₃ variability is mainly driven by meteorology, and interestingly, we can detect the fertilizers application period by looking at the NH₃ &#8211; temperature relationship. To check how well chemistry transport models perform during pollution events, we evaluate simulations made using the GEOS-Chem model for March 2011. In these simulations we find that NH₃ concentrations are overall underestimated, though day-to-day variability is well represented. PM_2.5 is generally underestimated over Paris and Mexico, but overestimated over Toronto.</p> <p>We use complementary information derived from IASI, and ground-based open-path measurements over Paris. We, therefore, assess the NH₃ temporal variabilities at different timescales (diurnal, seasonal, and interannual), to unravel NH₃ sources (agriculture and traffic) in Paris.</p>