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<p>Ammonia (NH<span class="inline-formula">₃</span>) is the most abundant alkaline compound in the atmosphere, with consequences for the environment, human health, and radiative forcing. In urban environments, it is known to play a key role in the formation of secondary aerosols through its reactions with nitric and sulfuric acids. However, there are only a few studies about NH<span class="inline-formula">₃</span> in Mexico City. In this work, atmospheric NH<span class="inline-formula">₃</span> was measured over Mexico City between 2012 and 2020 by means of ground-based solar absorption spectroscopy using Fourier transform infrared (FTIR) spectrometers at two sites (urban and remote). Total columns of NH<span class="inline-formula">₃</span> were retrieved from the FTIR spectra and compared with data obtained from the Infrared Atmospheric Sounding Interferometer (IASI) satellite instrument. The diurnal variability of NH<span class="inline-formula">₃</span> differs between the two FTIR stations and is strongly influenced by the urban sources. Most of the NH<span class="inline-formula">₃</span> measured at the urban station is from local sources, while the NH<span class="inline-formula">₃</span> observed at the remote site is most likely transported from the city and surrounding areas. The evolution of the boundary layer and the temperature play a significant role in the recorded seasonal and diurnal patterns of NH<span class="inline-formula">₃</span>. Although the vertical columns of NH<span class="inline-formula">₃</span> are much larger at the urban station, the observed annual cycles are similar for both stations, with the largest values in the warm months, such as April and May. The IASI measurements underestimate the FTIR NH<span class="inline-formula">₃</span> total columns by an average of <span class="inline-formula">32.2±27.5</span> % but exhibit similar temporal variability. The NH<span class="inline-formula">₃</span> spatial distribution from IASI shows the largest columns in the northeast part of the city. In general, NH<span class="inline-formula">₃</span> total columns over Mexico City measured at the FTIR stations exhibited an average annual increase of <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M16" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">92</mn><mo>±</mo><mn mathvariant="normal">3.9</mn><mo>×</mo><msup><mn mathvariant="normal">10</mn><mn mathvariant="normal">13</mn></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="73pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="e73707c46a7b6c10dbbb918d72c2c615"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-14119-2022-ie00001.svg" width="73pt" height="14pt" src="acp-22-14119-2022-ie00001.png"/></svg:svg></span></span> molecules cm<span class="inline-formula">⁻²</span> yr<span class="inline-formula">⁻¹</span> (urban, from 2012 to 2019) and <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M19" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">8.4</mn><mo>±</mo><mn mathvariant="normal">1.4</mn><mo>×</mo><msup><mn mathvariant="normal">10</mn><mn mathvariant="normal">13</mn></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="76pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="82622775d6cd88e0fa1386c57f952fce"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-14119-2022-ie00002.svg" width="76pt" height="14pt" src="acp-22-14119-2022-ie00002.png"/></svg:svg></span></span> molecules cm<span class="inline-formula">⁻²</span> yr<span class="inline-formula">⁻¹</span> (remote, from 2012 to 2020), while IASI data within 20 km of the urban station exhibited an average annual increase of <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M22" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">38</mn><mo>±</mo><mn mathvariant="normal">7.6</mn><mo>×</mo><msup><mn mathvariant="normal">10</mn><mn mathvariant="normal">13</mn></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="73pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="30ca33eea9d52ebb0c2ecbb180d94908"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-14119-2022-ie00003.svg" width="73pt" height="14pt" src="acp-22-14119-2022-ie00003.png"/></svg:svg></span></span> molecules cm<span class="inline-formula">⁻²</span> yr<span class="inline-formula">⁻¹</span> from 2008 to 2018.</p>