Measurement report: Exploring NH₃ behavior in urban and suburban Beijing: comparison and implications

• Main Authors: Z. Lan, W. Lin, W. Pu, Z. Ma
• Format: Article
• Language: English
• Published: Copernicus Publications 2021-03-01
• Series: Atmospheric Chemistry and Physics
• Online Access: https://acp.copernicus.org/articles/21/4561/2021/acp-21-4561-2021.pdf

<p>Ammonia (NH<span class="inline-formula">₃</span>) plays an important role in particulate matter formation; hence, its atmospheric level is relevant to human health and climate change. Due to different relative distributions of NH<span class="inline-formula">₃</span> sources, concentrations of atmospheric NH<span class="inline-formula">₃</span> may behave differently in urban and rural areas. However, few parallel long-term observations of NH<span class="inline-formula">₃</span> exist to reveal the different behaviors of NH<span class="inline-formula">₃</span> concentrations at urban and rural sites in a same region. In this study, online ammonia analyzers were used to continuously observe atmospheric NH<span class="inline-formula">₃</span> concentrations at an urban site and a suburban site in Beijing from 13 January 2018 to 13 January 2019. The observed mixing ratio of NH<span class="inline-formula">₃</span> averaged <span class="inline-formula">21±14</span> ppb (range of 1.6–133 ppb) at the urban site and <span class="inline-formula">22±15</span> ppb (range of 0.8–199 ppb) at the suburban site. The NH<span class="inline-formula">₃</span> mixing ratios at the urban and suburban sites exhibited similar seasonal variations, with high values in summer and spring and low values in autumn and winter. The hourly mean NH<span class="inline-formula">₃</span> mixing ratios at the urban site were highly correlated (<span class="inline-formula"><i>R</i>=0.849</span>, <span class="inline-formula"><i>P</i>&lt;0.01</span>) with those at the suburban site; however, the average diurnal variations in the NH<span class="inline-formula">₃</span> mixing ratios at the urban and suburban sites differed significantly, which implies different contributions from NH<span class="inline-formula">₃</span> sources and sinks at the urban and suburban sites. In addition to the emission sources, meteorological factors were closely related to the changes in the NH<span class="inline-formula">₃</span> concentrations. For the same temperature (relative humidity) at the urban and suburban sites, the NH<span class="inline-formula">₃</span> mixing ratios increased with relative humidity (temperature). Relative humidity was the factor with the strongest influence on the NH<span class="inline-formula">₃</span> mixing ratio in different seasons at the two sites. The relationships between the NH<span class="inline-formula">₃</span> concentrations and temperature (relative humidity) varied from season to season and showed differences between the urban and suburban sites. The reasons for the different relationships need to be investigated in future studies. Higher wind speed mainly from the northwest sector lowered the NH<span class="inline-formula">₃</span> mixing ratios at both sites. Similarly to other primary pollutants in Beijing, the NH<span class="inline-formula">₃</span> mixing ratios were high when impacted by air masses from the southern sector.</p>