Highly quasi-monodisperse ag nanoparticles on titania nanotubes by impregnative aqueous ion exchange.

Silver nanoparticles were homogenously dispersed on titania nanotubes (NT), which were prepared by alkali hydrothermal methodology and dried at 373 K. Ag(+) incorporation was done by impregnative ion exchange of aqueous silver nitrate onto NT. First, Ag(+) ions incorporate into the layers of nanotube walls, and then, upon heat treatment under N(2) at 573 and 673 K, they migrate and change into Ag(2)O and Ag(0) nanoparticles, respectively. In both cases, Ag nanoparticles are highly dispersed, decorating the nanotubes in a polka-dot pattern. The Ag particle size distribution is very narrow, being ca. 4 +/- 2 nm without any observable agglomeration. The reduction of Ag(2)O into Ag(0) octahedral nanoparticles occurs spontaneously and topotactically when annealing, without the aid of any reducing agent. The population of Ag(0) nanoparticles can be controlled by adjusting the annealing temperature. An electron charge transfer from NT support to Ag(0) nanoparticles, because of a strong interaction, is responsible for considerable visible light absorption in Ag(0) nanoparticles supported on NT.

A predictive model to correlate fuel specifications with on-road vehicles emissions in Mexico.

Mexico is currently in the process of implementing its third air management program, which includes control measures targeting emissions reductions from mobile, point, and area sources. Achieving the program goals will require changes in the composition and in physical properties of gasoline and implementing an emissions reduction schedule. For that purpose a study was undertaken to support understanding of the effect of gasoline fuel parameters on exhaust emissions. Specifically, the relative impacts of Reid vapor pressure, distillation parameters, oxygen, sulfur, olefins, and aromatic contents on the exhaust emissions of in-use vehicles of the metropolitan area of Mexico City were investigated. The results were used to develop a model to predict CO, nitrogen oxides, total hydrocarbons, and toxic emissions such as benzene, 1,3-butadiene, formaldehyde, and acetaldehyde. Also a statistical model that predicts evaporative emissions was built. Results of the present model are compared with those obtained using the complex model of the United States Environmental Protection Agency.

Assessment of new vehicles emissions certification standards in the metropolitan area of Mexico City.

Light duty gasoline vehicles account for most of CO hydrocarbons and NOx emissions at the Metropolitan Area of Mexico City (MAMC). In order to ameliorate air pollution from the beginning of 2001, Tier 1 emission standards became mandatory for all new model year sold in the country. Car manufacturers in Mexico do not guarantee the performance of their exhaust emissions systems for a given mileage. The purpose of this study was to assess whether the Tier 1 vehicles will stand the certification values for at least 162000 km with the regular fuel available at the MAMC. Mileage accumulation and deterioration show that certified carbon monoxide emissions will stand for the useful life of the vehicles but in the case of non-methane hydrocarbons will be shorter by 40%, and nitrogen oxides emissions above the standard will be reached at one third of the accumulated kilometers. The effect of gasoline sulfur content, on the current in use Tier 1 vehicles of the MAMC and the impact on the emissions inventory in year 2010 showed that 31000 extra tons of NOx could be added to the inventory caused by the failure of the vehicles to control this pollutant at the useful life of vehicles.

Air emissions assessment from offshore oil activities in Sonda de Campeche, Mexico.

Air emission data from offshore oil platforms, gas and oil processing installations and contribution of marine activities at the Sonda de Campeche, located at the Gulf of Mexico, were compiled and integrated to facilitate the study of long range transport of pollutants into the region. From this important region, roughly 76% of the total Mexican oil and gas production is obtained. It was estimated that the total air emissions of all contaminants are approximately 821,000 tons per year. Hydrocarbons are the largest pollutant emissions with 277,590 tons per year, generated during flaring activities, and SOx in second place with 185,907 tons per year. Marine and aviation activities contribute with less than 2% of total emissions. Mass of pollutants emitted per barrel of petroleum produced calculated in this work, are in the range reported by similar oil companies.

A driving cycle for vehicle emissions estimation in the metropolitan area of Mexico City.

A driving cycle derived from driving behavior and real traffic conditions in Mexico City (MC) is proposed. Data acquisition was carried out over diverse MC routes, representing travel under congested and uncongested conditions, using the chase-car approach. Thirteen different on-road patterns, including the four main access roads to MC, trips in both directions and different timetables, a total of 108 trips spanning 1044 km were evaluated in this study. The MC cycle lasts 1360 seconds with a distance of 8.8 km and average speed of 23.4 km h(-1). Both maximum speed (73.6 km h(-1)) and maximum acceleration (2.22 km h(-1)s(-1)) are lower than those of the new vehicles certification employed in Mexico ,FTP-75 cycle., that is, the MC cycle exhibits less cruising time and more transient events than the FTP cycle. A total of 30 light duty gasoline vehicles were classified into different technological groups and tested in an FTP-75 and MC driving cycles in order to compare their emission factors A potential concern is that in Mexico manufacturers design vehicles to meet the emission standards in the FTP, but emission levels increase significantly in a more representative cycle of present driving patterns in the Metropolitan Area of Mexico City (MAMC). The use of a more representative cycle during certification testing, would provide an incentive for vehicle manufacturers to design emissions control systems to remain effective during operation modes that are not currently represented in the official test procedures used in the certification process. Based on the results of the study, the use of MC cycle, which better represents current day driving patterns during testing of vehicle fleets in emissions laboratories, would improve the accuracy of emissions factors used in the MAMC emissions inventories.

Remote sensing study of emissions from motor vehicles in the Metropolitan Area of Mexico City.

Remote sensing was employed for the first time to measure nitric oxide (NO) levels of on-road light-duty motor vehicles of the Metropolitan Area of Mexico City (MAMC). The sensor placed at 12 different sites also measured the concentration of CO2, CO, and total hydrocarbons (THC) in the exhaust emissions. A database was compiled containing 122 800 readings, of which 84 650 (69%) records were valid emissions measurements. CO, HC, and NO valid readings were 68.9, 63.4, and 62.9%, respectively, of the total attempted measurements. Furthermore, 42 822 vehicles were number-plate-matched to model year with the information provided by the Inspection/Maintenance Program. The mean emissions of total valid readings for CO, HC, and NO were determined to be 1.31 vol %, 440 ppm (propane), and 914 ppm, respectively. In 1991 and 1994, remote sensing measurements of CO and HC tailpipe emissions were performed in the MAMC in five different locations (30 000 valid readings). Large drops in both pollutants were observed for the intervening years, but sufficient vehicle information was not available at that time to fully explain the observed trends. Compared with those reports, our results point out to a steady decrease in CO and HC exhaust emissions with vehicle model year. The fleet emissions measured exhibit a gamma-distribution, with 10% of the most polluting fleet studied being responsible for 45%, 25%, and 29% of the CO, HC, and NO emissions, respectively. NO emissions in taxis are the highest among the vintage of vehicles, a matter of concern since according to the distance traveled per year, they represent 22% of the total activity in the MAMC.

Evaluation of the vehicle inspection/maintenance program in the Metropolitan Area of Mexico City.

The Inspection/Maintenance Program in the Metropolitan Area of Mexico City (MAMC) mandates a test every 6 months for all gasoline motor vehicles as one of the strategies to decrease emissions of vehicular pollutants. FTP-75 and ASM procedures were performed in our facilities to a fleet of 108 in-use motor vehicles before and after the approval of the I/M mandatory test When our laboratory-simulated ASM data were compared with those of the official certificate, a large difference was observed between them. On the other hand, audits at the test-only centers indicate poor maintenance of the analytical instruments and dynamometers. On the basis of our FTP results, an estimation of the emissions change for the MAMC fleet shows a net 4% decrease in CO emissions, while total hydrocarbons and NOx increased 9 and 8%, respectively. Our results indicate that the I/M system in the MAMC lacks the technical capability and investment to ensure that software and hardware are properly maintained, calibrated, and upgraded. Sometimes limited attention is paid to ensure adequate training of inspectors, auditors, and quality control staff.

Contribution of the gasoline distribution cycle to volatile organic compound emissions in the metropolitan area of Mexico City.

Gasoline distribution in the metropolitan area of Mexico City (MAMC) represents an area of opportunity for the abatement of volatile organic compound (VOC) emissions. The gasoline distribution in this huge urban center encompasses several operations: (1) storage in bulk and distribution plants, (2) transportation to gasoline service stations, (3) unloading at service stations' underground tanks, and (4) gasoline dispensing. In this study, hydrocarbon (HC) emissions resulting from breathing losses in closed reservoirs, leakage, and spillage from the operations just listed were calculated using both field measurements and reported emission factors. The results show that the contribution of volatile HC emissions due to storage, distribution, and sales of gasoline is 6651 t/year, approximately 13 times higher than previously reported values. Tank truck transportation results in 53.9% of the gasoline emissions, and 31.5% of emissions are generated when loading the tank trucks. The high concentration of emissions in the gasoline transportation and loading operations by tank trucks has been ascribed to (1) highly frequent trips from distribution plant to gasoline stations, and vice versa, to cope with excessive gasoline sales per gasoline station; (2) low leakproofness of tank trucks; and (3) poor training of employees. In addition, the contribution to HC evaporative and exhaust emissions from the vehicles of the MAMC was also evaluated.

Environmental implications on the oxygenation of gasoline with ethanol in the metropolitan area of Mexico City.

Motor vehicle emission tests were performed on 12 in-use light duty vehicles, made up of the most representative emission control technologies in Mexico City: no catalyst, oxidative catalyst, and three way catalyst. Exhaust regulated (CO, NOx, and hydrocarbons) and toxic (benzene, formaldehyde, acetaldehyde, and 1,3-butadiene) emissions were evaluated for MTBE (5 vol %)- and ethanol (3, 6, and 10 vol %)-gasoline blends. The most significant overall emissions variations derived from the use of 6 vol % ethanol (relative to a 5% MTBE base gasoline) were 16% decrease in CO, 28% reduction in formaldehyde, and 80% increase in acetaldehyde emissions. A 26% reduction in CO emissions from the oldest fleet (< MY 1991, without catalytic converter), which represents about 44% of the in-use light duty vehicles in Mexico city, can be attained when using 6 vol% ethanol-gasoline, without significant variation in hydrocarbons and NOx emissions, when compared with a 5% vol MTBE-gasoline. On the basis of the emissions results, an estimation of the change in the motor vehicle emissions of the metropolitan area of Mexico city was calculated for the year 2010 if ethanol were to be used instead of MTBE, and the outcome was a considerable decrease in all regulated and toxic emissions, despite the growing motor vehicle population.

Long-term efficiency of catalytic converters operating in Mexico City.

A 1999 ordinance by the Government of Mexico City bans 1993 model-year vehicles from on-road operation if their catalytic converters are not replaced with new ones. To validate the benefits of this action, we examined three issues related to exhaust emissions of vehicles equipped with catalytic converters. After selecting representative fleets of in-use vehicles, a comparison between emissions and catalyst efficiency in cars with two categories of exhaust emission limits was carried out. For that purpose, two fleets were selected, each made up of 10 vehicles run under similar conditions. A third, larger fleet with emissions control systems was used to evaluate and simulate real-world conditions of vehicles in a controlled laboratory. Finally, the aging effect on the catalytic converter was studied on vehicles run for 100,000 km, replacing their old emission control devices for new ones. The 1991-1992 model-year vehicles showed a high percentage of compliance with the corresponding emissions standard (90%) in comparison with 1993 model-year and later vehicles (Tier 0). However, NOx emissions were higher for the newer vehicles. Fifty percent of the 1991-1992 model-year vehicles evaluated under the official inspection/maintenance (I/M) procedure did not meet the regulated emissions standard when the results were compared with those of the U.S. Federal Test Procedure FTP-75. Our results suggest that the replacement of old catalytic converters with new ones will have little effect on decreasing polluting emissions because these vehicles were in very bad mechanical condition. Results of catalytic activity as a function of mileage indicated inefficient catalyst performance for the fleets tested. All pollutant conversions were below 90% efficiency, and they deteriorated by an average of 30% after the vehicles were run for 100,000 km.

Effect of methyl tertiary butyl ether concentrations on exhaust emissions from gasoline used in the metropolitan area of Mexico City.

In this work, the primary objective was to assess the impact of oxygenated fuel on the exhaust emissions from an important fraction of vehicles in the Metropolitan Area of Mexico City (MAMC). The results aim to provide information on the actual effect of MTBE on a fleet that represents more than 60% of the in-use vehicles in the MAMC. Ten vehicles were tested with a low-octane base gasoline, and 10 more with a regular-grade unleaded base gasoline. Three MTBE concentrations, 5, 10, and 15 vol %, were tested following the U.S. Federal Test Procedure (FTP). CO, total HC, and NOx from the exhaust gases were quantitatively evaluated and also characterized for FTP speciated organic emissions. From this data, the O3-forming potential of the fuels was calculated. Results show that for the fleet using low-octane gasoline, the addition of 10% MTBE substantially reduced CO emissions, but total HC concentration in the exhaust showed a modest decrease. For the regular gasoline, the 10% MTBE blend seemed to be the best choice, but there was not a significant decrease in emissions. The specific reactivity of each fuel, expressed in grams of O3 per gram of nonmethane organic gases, increased with MTBE concentration in both cases. This result is important to consider, especially for a region like Mexico City, which has high atmospheric O3 concentrations.

An evaluation of the LPG vehicles program in the metropolitan area of Mexico City.

The environmental agency in the metropolitan area of Mexico City has launched a program to introduce more energy-efficient modes of transport, one of which is the use of alternative and less polluting fuels. With the perspective in mind, a liquefied petroleum gas (LPG) fleet of vehicles is exempt of the mandatory "one day without a car" program if the emission of pollutants is below the standard authorized for that specific purpose. Today, about 28,000 light-duty vehicles and heavy-duty trucks circulate in the area, most of them as aftermarket converted vehicles. In this work, we evaluated regulated exhaust emission and other parameters on 134 representative vehicles of that fleet. From the data obtained, an estimate of emission factors and their contribution to the global emission in the metropolitan area is provided. It is concluded that more than 95% of the in-use vehicles using LPG presented regulated emissions which exceeded in one or more the environmental regulations values required for certification. The poor maintenance of the vehicles and the type of conversion kit installed could be the culprits of the results obtained.

Contribution of LPG-derived emissions to air pollution in the metropolitan area of Guadalajara City.

Measurements of hydrocarbon (HC) emissions generated by the use of liquefied petroleum gas (LPG) in the metropolitan area of Guadalajara City (MAG) are presented in this work. Based on measurements in the course of distribution, handling, and consumption, an estimated 4407 tons/yr are released into the atmosphere. The three most important contributors to LPG emissions were refilling of LPG-fueled vehicles and commercial and domestic consumption. The MAG shows a different contribution pattern of LPG emission sources compared with that of the metropolitan area of Mexico City (MAMC). These results show that each megacity has different sources of emissions, which provides more accurate strategies in the handling procedures for LPG to decrease the impact in O3 levels. This work represents the first evaluation performed in Guadalajara City, based on current measurements, of the LPG contribution to polluting emissions.

Exhaust Emissions from Gasoline- and LPG-Powered Vehicles Operating at the Altitude of Mexico City.

Unburned hydrocarbons (HCs), carbon monoxide (CO), and oxides of nitrogen (NOx) are the compounds regulated as pollutants by an environmental standard in the Metropolitan Area of Mexico City (MAMC). The main fuel used in vehicular transportation is gasoline, and the use of liquefied petroleum gas (LPG) is now an alternative as low emission technology to decrease the environmental impact of transportation operations. The environmental impact of commercial gasoline consumption in the Valley of Mexico was estimated by on-road and FTP-75 testing of three formulations of gasoline (one leaded [octane 81] and two unleaded [one octane 87 and one octane 93]). A fleet of 30 vehicles was used: 10 were chosen that had pre-1990 technology, while 12 were 1991-1996 vehicles equipped with fuel injection, catalytic converters, and air/ fuel ratio control technology. The remaining eight vehicles were high-performance new model vehicles (1995-1996) equipped with the newest technology available for pollution control. Fifteen vehicles in the fleet were also tested for the effect of changing from leaded to unleaded gasoline. Three different LPG formulations were tested using three vehicles representative of the LPG-powered fleet in the MAMC. Two gasoline-to-LPG conversion certified commercial systems were evaluated following the BAR-90 and the HOT-505 procedures. Emissions corresponding to the high-octane (premium) gasoline showed a 15% higher contribution to HCs with a 6% lower reactivity than the 87 octane gasoline; the HCs in the exhaust for premium gasoline are mainly isoparaffins. When the vehicles were tested on the road at high speeds, an average 3% increase in mileage was obtained when vehicles were switched from leaded to unleaded gasoline, while a 5% increase in mileage was observed when vehicles were switched from 87 octane to premium gasoline. The tests of LPG formulations indicated that a change in composition from 60% vol of propane to 85.5% vol reduces levels of HCs and CO emissions; such is not the case for the NOx emissions. The higher the concentration of propane, the higher the levels of NOx that reached values above the maximum limits set by the environmental standard. A value of 70% vol of propane in the LPG mixture, with variations no greater than 4%, seems to be the best method for reducing pollutant emissions in Mexico City.

[Preferential habits of consumers of common bean (Phaseolus vulgaris L.) in Mexico]. / Hábitos preferenciales de los consumidores de frijol común (Phaseolus vulgaris L.) en México.

A detailed knowledge of the consumer's preferences for the different classes of common bean is useful to define objectives in bean breeding and quality projects in a given region or country and it is also a valuable tool to design marketing strategies. The present work consisted on the application of a survey to 1514 common bean consumers in 14 states of Mexico. To facilitate the interpretation of the results the country was divided in four regions: North East, North West, Center and South. In the North West region, 98% of the surveyed individuals eat the "Azufrado" types (sulphur yellow); in the North East, 70% of the consumers prefer "pinto" (beige with brown mottles) and "Bayo" (cream) types; in the South, 90% of the consumers prefer the "Black" type; and in the Center of the country, all commercial classes are consumed. Within a commercial class, specific characteristics are demanded. For instance, in the black type, small and opaque seeds are preferred while in the "Flor de mayo" (Beige with pink mottles) type medium to large seeds having bright seed coat are preferred. The main characteristics utilized by consumers to select a given bean type are cooking time and flavor. It was observed that preferential classes are well established among the consumers since 70% responded that they would not change the preferred class even if the alternative class was sold to a lower price. Consumers do not soak the beans, because it changes the flavor and the aspect of the cooked beans and they do not add salt at the beginning of the cooking process due to the same reason. Organoleptic studies conducted in the laboratory confirmed that soaking of beans or addition of salts in the soaking water or at the beginning of the cooking process negatively affected acceptability of cooked beans by panelists. In this paper aspects related to ways of processing and consuming common beans as well as marketing aspects are discussed.