Chemical Composition of Wet Atmospheric Deposition in a Natural Urban Reserve, Conservation of Green Urban Areas: a Mexico City Case Study

Abstract

Green areas are essential for life in cities and for the conservation of ecosystem services in the case of megacities such as Mexico City. Green areas mitigate air pollution, reduce the temperature, and promote infiltration to feed the aquifers that, in the case of Mexico City, supply 68% of the water. Additionally, food production and recreational usage are important for the population. In the years 2017 and 2018, the chemical composition of wet deposition in the southern part of Mexico City was analyzed, daily and weekly. The study area is located in the greenest part of Mexico City, an important site for water recharge and carbon sequestration. Mexico City, like other megacities of high- and low-income countries, faces serious problems of air pollution. The purpose of this study was to measure the amount of total nitrogen and sulfur that is available in a natural reserve located inside the National Autonomous University of Mexico, and conductivity, pH, rain volume, and anions and cations were analyzed as well. Eighteen months of data were analyzed in order to understand the atmospheric deposition in and anthropogenic influence on an urban green natural area from the southern part of the city. Although both stations are less than 2 km apart, there are significant differences in their chemical composition; however, no differences were found for precipitation and pH, indicating that each station provides a local contribution, depending on local events and sources. Samples included rain events match for both sampling sites, with 67% of the samples in the same rain event match. Nonetheless, when only volume is compared for each year, both tests showed no significant difference (pv = 0.520). Throughout the year, various rainfall rates occur at the CU-CCA and REPSA stations, and the rainy season presents during the May–October period; the median value registered for both monitoring stations was 780 mL, and maximal rainfall was 4780 mL presenting at the CU-CCA station.