The Importance and First Results of Assessing Mercury in Ambient Air in Mexico City

Abstract Description: Mexico City, with more than 20 million inhabitants, in addition to the large number of sources of atmospheric pollution that exist, has always represented a challenge in terms of air quality. Monitoring of criteria contaminants has been carried out for several decades, however a systematic evaluation of toxic pollutants is lacking. Because Mexico is a signatory of the Minamata agreement, it must pay attention to the toxic pollutant that is mercury.

The impact of mercury on the environment has long been widely known: air, water and soil, as well as its concentrating effect in food chains. Likewise, the complexity of its measurement must be recognized, especially due to technical difficulties and of course the cost involved in the measurement. In the case of the determination of mercury in ambient air, the National Atmospheric Deposition Program (NADP) carries out its measurement through the Atmospheric Mercury Network (AMNet).

The National Autonomous University of Mexico (UNAM) collaborates with NADP in the lines of research on the assessment of wet atmospheric deposition in some regions of North America, the evaluation of reactive nitrogen in ambient air and in wet atmospheric deposition and, starting in 2023, in the measurement of mercury in ambient air, having installed a Tekran analyzer at the air quality monitoring station located at the Institute of Atmospheric Sciences and Climate Change (ICAyCC) of the UNAM.

The monitoring of mercury in ambient air began on June 6, 2023, and through March 8, 2024, made 74,576 meaurements of elemental mercury concentration every 5 minutes. The data analysis corresponded to different levels of validation according to US-EPA protocols. The maximum concentrations of mercury were 10 to 20 ng/m3 for some days, with the minimum concentration of 1.33 ng/m3. The average and median of the study period were 3.33 and 3.10 ng/m3, respectively. A daily average concentration of 3.31 ng/m3 and a median of 3.14 ng/m3 over the 276 days of monitoring. Finally, the maximum mercury concentration of 20.36 ng/m3 was recorded on Wednesday, followed by Thursday with 15.85 ng/m3 and Monday with 15.69 ng/m3.

It is worth mentioning that the monitoring site at UNAM corresponds to a school activity in an urban area. It is also recommended to increase the number of sites for measuring mercury in ambient air in industrial areas and in regions of international interest such as the Gulf of Mexico.