L.G. Ruiz-Suárez

Short-term ozone forecasting by artificial neural networks

Abstract In this work we report preliminary results of a study aiming to develop an intelligent tool for performing ozone forecasting in the polluted atmosphere of Mexico City. This tool is based in the paradigm of neural networks. Two neural models are used in this work, namely, the Bidirectional Associative Memory (BAM) and the Holographic Associative Memory (HAM). We analyse and preprocess daily patterns of meteorological variables and concentrations of pollutants as measured by five monitoring stations in Mexico City. These patterns are used to train both neural networks and then we use them to predict ozone at one point in the city. Preliminary results are reported and some conclusions are drawn.

Evaluation of vapor recovery systems efficiency and personal exposure in service stations in Mexico City

Results of a field study on the efficiency of vapor recovery systems currently used in gasoline service stations in Mexico City are presented. Nine gasoline stations were studied, representing the several technologies available in Mexico City. The test was applied to a fixed vehicular fleet of approximately 10 private and public service vehicles. Each one of the gasoline service stations tested reported efficiencies above 80% in the recovery of vapor losses from gasoline which is the minimum permissible value by Mexican regulations. Implications to the emissions inventory are discussed. A second goal of this study was to measure the potential exposure of service attendants to three important components of gasoline: benzene; toluene; and xylenes. The influence of spatial location of personnel within the service station was also evaluated by measuring levels of the three compounds both at the refueling area and in the service station office. Results are discussed and compared to a previous study.

Sensitivity analysis of a UV radiation transfer model and experimental photolysis rates of NO2 in the atmosphere of Mexico City

Abstract Photolysis of key species such as nitrogen dioxide, ozone and aldehydes, are the elementary reactions leading to the formation of photochemical smog. Calculations and experimental measurements (in particular, nitrogen dioxide) of these key reactions are reported, as well as, the sensitivity of them to the ozone column, local albedo and properties of the urban aerosol layer in Mexico City. A radiation transfer model (RTM ), based on the delta-Eddington approximation, was used in the calculations. The results show the importance of providing local resolution for photolysis rates by considering different local conditions within the modeling domain of air quality models.

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.

Photolytic rates for NO2, O3 and HCHO in the atmosphere of Mexico City

Abstract We report theoretical calculations of photolysis rates for NO 2 , O 3 and HCHO in the atmosphere of Mexico City. To estimate the radiance needed in the calculations, the equation of transfer is solved by the delta-Eddington method. An atmosphere of air, NO 2 , O 3 and dry aerosols is modeled.

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 IPCCs methodology for emissions from enteric fermentation are discussed and an intermediate procedure is proposed. These methods could also be applied in other countries.

Do we need an Ad hoc chemical mechanism for Mexico City's photochemical smog?

Chemical mechanisms in mathematical models for air quality studies represent the synthesis of about 30 years of research in gas kinetics and atmospheric chemistry, and are able to represent, to a good extent, the chemistry of photochemical smog. However, due to the large amount of computer resources required by these models, different well-known approaches have been used in order to make them operative. In any of these approaches, a set of educated guesses is made, based upon the knowledge of the conditions under which the reactions occur and the competition between them, and upon the expected absolute and relative concentrations of the emitted reactive organic gases (ROG)

The influence of the Tula, Hidalgo complex on the air quality of the Mexico City Metropolitan Area

Using an air quality model, this study shows how emissions from the “Miguel Hidalgo” refinery of Petroleos Mexicanos (Pemex) and the thermoelectric plant “Francisco Perez Rios” of the Comision Federal de Electricidad (CFE, Federal Electricity Commission) in Tula, Hidalgo influence the atmosphere of the Mexico City Metropolitan Area (MCMA). The model couples meteorology and chemistry. The weather scenario encompasses the period from October 20-28, 2005. Two scenarios are compared: the first assumes a 40% reduction in emissions of NOx, SO2, and volatile organic compounds (VOCs) from the Tula complex (reduction scenario), and the second considers the scenario without reduction (baseline scenario). The model is compared with measurements of the Red Automatica de Monitoreo Atmosferico (Automatic Environmental Monitoring Network). We observe that under certain weather conditions, the energy sector of Tula, Hidalgo affects the air quality in the MCMA. The reduction scenario is effective in reducing SO2 concentrations; however, despite a 40% decrease in the emissions of ozone precursors, their concentrations in the MCMA did not decrease.

Mapping recession risk for cultural heritage stone in Mexico City due to dry and wet deposition of urban air pollutants

Air pollution is a threat to cultural heritage because it accelerates the natural deterioration of monuments, palaces, churches, and archaeological ruins, which have an irreplaceable value. In the Mexico City Metropolitan Area (MCMA), there are 19 968 buildings registered as archaeological, historic, or artistic monuments. Some are built with calcareous rocks (limestone and marble) but many of them are made with andesite, tezontle and tuff stone. This paper reports for the first time the spatial distribution of the potential risk of deterioration on calcareous rocks in terms of surface recession with regard to Mexican cultural heritage in the MCMA for the base year 2007. The risk estimate was performed using Lipfert’s damage function, only applicable to carbonate stones of medium and low porosity. These include mainly medium/high density limestone and marble. Carrara white marble has a density of 2.69 g cm –3 and a porosity of 0.37%, and limestone has a density of 2.2-2.6 g cm –3 and a porosity of 5-20%. For high porosity (low density) limestone the function would be applicable with a potential under-estimation. In this function, annual recession rate is a function of annual averages of precipitation, pH, and dry deposition of SO 2 and HNO 3 . Data from several meteorological monitoring networks, the MCMA air quality and acid deposition monitoring networks, and a 3D air quality model (MCCM) were interpolated in a GIS in order to obtain map layers for these variables. These overlaid maps were used to apply the Lipfert functions at the specific coordinates of a small sample of relevant historic or artistic monuments. The complexity of climate gradients, wind patterns, and emissions distribution within the Mexico Megacity leads to gradients as large as 50% in estimated recession rates using the Lipfert function at nearby sites made of the same type of building materials. The Comision Ambiental de la Megalopolis (Environmental Commission of the Megacity) divides the MCMA into five sectors. Differences in recession rates between them were, in 1990, as large as those between estimated values for Oviedo, Paris, and Prague in Europe for the period 1980-2000. Recession rates decreased by about 50% from 1990 to 2007, the base year for this report, due to the success of air pollution control actions focused on the protection of public health. Nevertheless, strong recession gradients are still expected for carbonate stone within the MCMA. The recession values reported in this work must be taken as conservative estimates due to the not yet optimal performance of 3D air quality models in urban meteorology and the high degree of uncertainty in modeling emissions inventories. Most notable is the SO 2 emissions inventory. These maps call for a program of experimental determination of recession rates for building materials that comprise a very large part of Mexico’s unique cultural heritage. These maps should also be added to the critical level maps obtained for human exposure, crops, and ecosystems in order to properly estimate the actual cost of air pollution in the MCMA and the area under its influence.