Abstract
Abstract. In order to expand the currently limited understanding of atmospheric mercury source-receptor relationships in the Mexico City Metropolitan Area, real time measurements of atmospheric mercury were made at a downtown urban site, and a rural site on the outskirts of Mexico City, during March 2006. Numerous short-lived increases in particulate mercury (PHg) and reactive gaseous mercury (RGM) concentrations were observed at the urban site during the 17 day study, and less frequent increases in gaseous elemental mercury (GEM) concentrations were measured at both the urban and rural sites. The episodic increases observed were attributed to plume impacts from industrial point source emissions in and around Mexico City. Average concentrations and standard deviations measured during the study were as follows: i) urban site; PHg=187±300 pg m−3, RGM=62±64 pg m−3, GEM=7.2±4.8 ng m−3, and; ii) rural site; GEM=5.0±2.8 ng m−3. Several source regions of atmospheric mercury to the urban and rural sites were determined using Concentration Field Analysis, in which atmospheric mercury measurements were combined with back trajectory data to determine source regions. Only some source regions correlated to mercury emission sources listed in the Federal Pollutant Release and Transfer Register, leaving the rest unaccounted for. Contributions of anthropogenic mercury point sources in and around Mexico City to concentration averages measured at the urban site during the study were estimated to be: 93±3% of reactive mercury (PHg and RGM), and; 81±0.4% of GEM. Point source contributions to GEM measured at the rural site were 72±1%. GEM and reactive mercury (PHg+RGM) were not found to correlate with biomass burning at either of the measurement sites.
Highlights
It is important to recognize that the Concentration Field Analysis (CFA) results from this study provide perspective of how point sources in and around the Mexico City Metropolitan Area (MCMA) affect atmospheric mercury concentrations at the measurement sites
Point sources included in the 2004 Federal Pollutant Release and Transfer Register (PRTR) correlated well with source regions determined using Concentration Field Analysis, illustrating the impact of facilities in and around Mexico City on atmospheric mercury measurements at the urban and rural sites
Extensive source regions were identified that did not correlate to entries in the PRTR and which contributed substantially to average reactive mercury and gaseous elemental mercury concentrations at the urban site
Summary
Rutter et al.: Atmospheric mercury source regions in Mexico City mercury levels than less urbanized regions due to high densities of energy production, industrial activities, and refuse incineration (Gabriel et al, 2005; Lynam and Keeler, 2005). The Mexico City Metropolitan Area (MCMA) is the second largest urban center in the world, has a high concentration of heavy industry, and is located in a basin at high altitude surrounded by mountains on three sides, which include a volcano, a likely emission source of natural mercury (Bagnato et al, 2007). Given the poor air quality, concentration of industry, and the presence of a volcano in the basin, Mexico City atmospheric mercury concentrations are likely to be substantially increased over rural background concentrations.
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