Study of the regional air quality south of Mexico City (Morelos state)

Results from the first study of the regional air quality in Morelos state (located south of Mexico City) are presented. Criteria pollutants concentrations were measured at several sites within Morelos in February and March of 2007 and 2009; meteorological data was also collected along the state for the same time periods; additionally, a coupled meteorology-chemistry model (Mesoscale Climate Chemistry Model, MCCM) was used to gain understanding on the atmospheric processes occurring in the region. In general, concentrations of almost all the monitored pollutants (O(3), NO(x), CO, SO(2), PM) remained below the Mexican air quality standards during the campaign; however, relatively high concentrations of ozone (8-hour average concentrations above the 60 ppb level several times during the campaigns, i.e. exceeding the World Health Organization and the European Union maximum levels) were observed even at sites with very low reported local emissions. In fact, there is evidence that a large percentage of Morelos vegetation was probably exposed to unhealthy ozone levels (estimated AOT40 levels above the 3 ppm h critical limit). The MCCM qualitatively reproduced ozone daily variations in the sites with an urban component; though it consistently overestimated the ozone concentration in all the sites in Morelos. This is probably because the lack of an updated and detailed emission inventory for the state. The main wind patterns in the region corresponded to the mountain-valley system (downslope flows at night and during the first hours of the day, and upslope flows in the afternoon). At times, Morelos was affected by emissions from surrounding states (Distrito Federal or Puebla). The results are indicative of an efficient transport of ozone and its precursors at a regional level. They also suggest that the state is divided in two atmospheric basins by the Sierras de Tepoztlán, Texcal and Monte Negro.

Observations of formic and acetic acids at three sites of Mexico City

Levels of atmospheric carboxylic acids in gas and particulate matter were measured at three sites in Mexico City within the month of March 2000. An annular denuder system was used for sampling and the analytical method was HPLC with UV detection. Formic and acetic acids were present in the PM2.5 fraction and in the gas phase. Total concentration of formic acid was between 0 and 7 ppbV and total concentration of acetic acid was between 1 and 17 ppbV. On average 53% of the formic acid and 67% of the acetic acid were present in particulate matter.

Methane emission factors from cattle manure in Mexico

Factors responsible for methane emission from cattle manure representing diverse climates, systems and functions of cattle production are presented. These factors were obtained by means of an experimental methodology developed for this project. It was considered that the temperature, moisture, handling of manure and the animals' feed ration affect methane production. Drying conditions and fermentation of manure in cool, temperate and warm climates were simulated in the laboratory. Cattle manure was obtained from animals in intensive, semi-intensive and extensive production systems; for dairy, non-dairy and double purpose cattle production functions. Also handling of manure in dry lot, pasture and solid storage was considered. Results suggest that the dominant factor in methane emissions is the feed ration, followed by fermentation temperature and the excreta moisture content. The emission factors obtained in this work are at least a factor of five smaller than those proposed in the revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories for countries like Mexico.

Modeling methane emissions from cattle in Mexico

Modeling methane emissions from cattle requires data on herd size, herd distribution by weight and use, and distribution by climate. In this article, it is shown how empirical and semi-empirical models were obtained for these data in Mexico. Some shortfalls in the Tier 2 approach of the 1994 IPCC's methodology for emissions from enteric fermentation are discussed and an intermediate procedure is proposed. These methods could also be applied in other countries.