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Multiscale observations of NH3 around Toronto, Canada

Abstract : Ammonia (NH 3) is a major source of nitrates in the atmosphere, and a major source of fine particulate matter. As such, there have been increasing efforts to measure the atmospheric abundance of NH 3 and its spatial and temporal variability. In this study, long-term measurements of NH 3 derived from multiscale datasets are examined. These NH 3 datasets include 16 years of total column measurements using Fourier transform infrared (FTIR) spectroscopy, three years of surface in-situ measurements , and 10 years of total column measurements from the Infrared Atmospheric Sounding Interferometer (IASI). The 5 datasets were used to quantify NH 3 temporal variability over Toronto, Canada. The multiscale datasets were also compared to assess the observational footprint of the FTIR measurements. All three time series showed positive trends in NH 3 over Toronto: 3.34 ± 0.46 %/year from 2002 to 2018 in the FTIR columns, 8.88 ± 2.83 %/year from 2013 to 2017 in the surface in-situ data, and 8.38 ± 0.77 %/year from 2008 to 2018 in the IASI columns. To assess the observational footprint of the FTIR NH 3 columns, correlations between the datasets were exam-10 ined. The best correlation between FTIR and IASI was obtained with coincidence criteria of ≤ 25 km and ≤ 20 minutes, with r = 0.73 and a slope of 1.14 ± 0.06. Additionally, FTIR column and in-situ measurements were standardized and correlated. Comparison of 24-day averages and monthly averages resulted in correlation coefficients of r = 0.72 and r = 0.75, respectively, although correlation without resampling to reduce high-frequency variability led to a poorer correlation, with r = 0.39. The GEOS-Chem model, run at 2°× 2.5°resolution, was compared against FTIR and IASI to assess model performance 15 and investigate correlation of observational data and model output, both with local column measurements (FTIR) and measurements on a regional scale (IASI). Comparisons on a regional scale (a domain spanning 35°N to 53°N, and 93.75°W to 63.75°W) resulted in r = 0.57, and thus a coefficient of determination, which is indicative of the predictive capacity of the model, of r 2 = 0.33, but comparing a single model grid point against the FTIR resulted in a poorer correlation, with r 2 = 0.13, indicating that a finer spatial resolution is needed for modeling NH 3 .
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Shoma Yamanouchi, Camille Viatte, Kimberly Strong, Erik Lutsch, Dylan B. A. Jones, et al.. Multiscale observations of NH3 around Toronto, Canada. Atmospheric Measurement Techniques, European Geosciences Union, In press, ⟨10.5194/amt-2020-319⟩. ⟨insu-02926968⟩

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