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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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Submitted on : Friday, February 5, 2021 - 4:42:30 PM
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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, 2021, 14 (2), pp.905-921. ⟨10.5194/amt-14-905-2021⟩. ⟨insu-02926968v2⟩



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