Violeta Mugica

Hydrocarbon source apportionment in Mexico City using the chemical mass balance receptor model

Abstract A field study was conducted in Mexico City during May–November 1997 to determine non-methane hydrocarbons (NMHC) species emitted from different sources: application of slow curing asphalt pavement, liquefied petroleum gas (vapour phase), dry cleaning, graphic arts, landfill, emissions of motor vehicle exhaust inside a tunnel, hot soak, whole gasoline, painting operations and degreasing. Forty-five ambient air samples of NMHC were simultaneously collected from 6:00 to 9:00 a.m. at three different sites, Xalostoc, Pedregal and La Merced, denominated receptors, during the spring and fall of 1996. In both cases samples were collected in stainless-steel canisters and analysed by gas chromatography with flame ionisation detection system. Based on these measurements the chemical mass receptor model (CMB) was applied to estimate the contribution of the different NMHC source to ambient pollution. The average results for the two sampling periods showed that the major sources of NMHC for the three sites were: motor vehicle exhaust with an average contribution of 54.9, 57.4 and 63.8% for Xalostoc, Pedregal and La Merced, respectively, followed by handling and distribution of liquefied petroleum gas with 28.5% in Xalostoc, 20.0% in Pedregal and 24.0% in La Merced.

Chemical composition of fugitive dust emitters in Mexico City

The gravimetric and chemical composition of fugitive dust emitters of Mexico City were analyzed to determine the particulate matter source profiles. Samples of geological material, unpaved and paved roads, agricultural soil, dried lake, asphalt, cement plants, landfill, gravel, and tezontle soil, were collected directly from the ground using a broom and a dustpan. These were dried, sieved and taken through a laboratory resuspension chamber to emulate the natural wind-blown processes of bulk soils and also to provide a uniform deposit on Teflon membrane and quartz fiber filters for further gravimetric and chemical analyses of PM2.5 and PM10 size fractions. Chemical analyses of the filters included X-ray fluorescence for elemental composition, ion chromatography for water soluble anions, atomic absorption for water soluble metals, automated colorimetric analysis for ammonium and thermal/optical reflectance analysis for carbon species. The data show that most fugitive emitters are composed of 20–30% PM2.5, which is relatively less than the reported contribution by fossil fuels and biomass (40–60%).

Temporal and spatial variations of metal content in TSP and PM10 in Mexico City during 1996–1998

Abstract Metal constituents of filters collected from 1996 through 1998 from five monitoring network stations of Mexico City, were identified using ionization argon coupled plasma. Nine metals were quantified: cadmium, chromium, copper, manganese, nickel, lead, titanium, iron and vanadium. The statistical analysis shows that in general the metal concentration diminished from 1996 to 1998 in total suspended particles and PM10 although there are some exceptions. The correlation between TSP and PM10 shows that there is a higher proportion of metals in the respirable fraction than in the particles with bigger diameter. Lead content did not exceed the standard concentration of 1.5 μg/m 3 ; with an average value of 0.09 in PM10 and 0.17, in TSP and the highest values of this metal were 1.03 and 0.96 for PM10 and TSP, respectively, both in January of 1996. The study of size and shape by scanning electronic microscopy led us to identify particles from natural soils and clays, from combustion and from industrial processes.

Determination of Motor Vehicle Profiles for Non-Methane Organic Compounds in the Mexico City Metropolitan Area

Non-methane organic compound (NMOC) profiles for on-road motor vehicle emissions were measured in a downtown tunnel and parking garages in Mexico City during 1996. Hydrocarbon samples from the tunnel and ambient air samples (C2-C12) were collected using stainless steel canisters, and carbonyl compounds were collected using 2,4-dinitrophenylhydrazine (DNPH) impregnated cartridges. Canister samples were analyzed by gas chromatog-raphy/flame ionization detection (GC/FID) to ascertain detailed hydrocarbon composition. DNPH samples were analyzed by high performance liquid chromatography (HPLC). NMOC source profiles were quantified for evaporative emissions from refueling, cold start, and hot soak, and on-road operating conditions. The ultimate purpose will be to determine the apportionment of ambient NMOC concentrations using the Chemical Mass Balance (CMB) model. The tunnel profile contained 42.3 ppbC% of alkanes, 20.6 ppbC% of unsaturated compounds, and 22.4 ppbC% of aromatics. The most abundant species were acetylene with 7.22 ppbC%, followed by ipentane with 5.69 ppbC%, and toluene with 5.42 ppbC%. These results were compared with those from studies in the United States. The cold start profile was found to be similar to the tunnel profile, although there were differences in the content of acetylene, isopentane, and oxygenates. The abundance of saturated NMOC in the hot soak profile was similar to gasoline head space profiles; it was also much larger than saturated NMOC in the roadway profile.

Speciated non-methane organic compounds emissions from food cooking in Mexico

Abstract Non-methane organic compound (NMOC) emissions from different sorts of food preparation sites, were quantified for the first time in Mexico, in order to develop emission profiles for further application in the chemical mass balance receptor model (CMB). Restaurants using charcoal grills and LP gas stoves, “tortillerias”, food frying places and rotisseries were sampled using SUMMA ® stainless-steel canisters to analyse NMOC by high-resolution gas chromatography. The results obtained show that profiles determined from food cooking processes have similarities to those found in LP gas combustion, which is the most common fuel in Mexico used for this purpose, although there were differences in the relative composition of propane and butane in both cases. This suggests that, the rates of combustion of propane and butane are different. It has also been detected that propene, a reactive olefin is produced during the combustion process. The obtained profiles of restaurants, rotisseries and fried food show an important contribution of two carbon compounds (ethane, ethylene and acetylene) that can be attributed to the complex process of grease and meat cooking. The presence of these compounds cannot be attributed to vehicular sources since the concentrations are higher than in ambient air. These were also determined from aromatic compounds such as benzene, toluene and xylene in the combustion of vegetal charcoal. The measured concentrations indicate that NMOC emissions from cooking may become an important indoor source of NMOC under crowded conditions in closed places.

Seasonal variation of polycyclic aromatic hydrocarbon exposure levels in Mexico City.

Abstract This work presents the results obtained when determining the priority polycyclic aromatic hydrocarbon (PAH) concentration contained in particulate matter 10 μm in aerodynamic diameter or less (PM10) and in the gas phase in Mexico City’s atmosphere by means of a field study conducted during 2005. PM10 and vapor-phase PAHs were collected on prebaked quartz fiber filters and PUF-XAD-4 resin and quantified by gas chromatography (GC)-mass spectrometry. Vapor-phase PAHs comprised 86–97% of the total PAH mass, and naphthalene was the most abundant PAH determined, contributing 84–93% to the total mass. The benzo[a]pyrene content was on average 7% of the PAHs’ particle phase and 0.2–1% of the gas phase. The PAH concentrations measured where large industrial areas are located were 2–8 times greater during the fall/winter months (dry-cold season), when winds bear north- north-easterly, than in spring and summer. In contrast, the largest partition gas/particle ratio occurred during the dry-warm season (March–May). The results of statistical analysis using multivariate techniques suggest that motor vehicles are the main PAH contributors. The toxicity equivalence factors (TEFs) related to the carcinogenic benzo[a]pyrene potency were used for the assessment of the carcinogenic potential risk because of the measured airborne PAHs. Benzo[a]pyrene equivalent (BAPeq) concentrations were determined through multiplication of the individual PAH concentrations by their corresponding TEF value. The estimated total BAPeq for the whole field study considering only PM10 PAHs was 1085 pg m-3.However, when taking into account the PAHs in both phases, the estimated total BAPeq was 1250 pg m-3; in either case, the values were greater than the 1000-pg m-3 limit proposed by European countries.

Receptor Model Source Apportionment of Nonmethane Hydrocarbons in Mexico City

With the purpose of estimating the source contributions of nonmethane hydrocarbons (NMHC) to the atmosphere at three different sites in the Mexico City Metropolitan Area, 92 ambient air samples were measured from February 23 to March 22 of 1997. Light- and heavy-duty vehicular profiles were determined to differentiate the NMHC contribution of diesel and gasoline to the atmosphere. Food cooking source profiles were also determined for chemical mass balance receptor model application. Initial source contribution estimates were carried out to determine the adequate combination of source profiles and fitting species. Ambient samples of NMHC were apportioned to motor vehicle exhaust, gasoline vapor, handling and distribution of liquefied petroleum gas (LP gas), asphalt operations, painting operations, landfills, and food cooking. Both gasoline and diesel motor vehicle exhaust were the major NMHC contributors for all sites and times, with a percentage of up to 75%. The average motor vehicle exhaust contributions increased during the day. In contrast, LP gas contribution was higher during the morning than in the afternoon. Apportionment for the most abundant individual NMHC showed that the vehicular source is the major contributor to acetylene, ethylene, pentanes, n-hexane, toluene, and xylenes, while handling and distribution of LP gas was the major source contributor to propane and butanes. Comparison between CMB estimates of NMHC and the emission inventory showed a good agreement for vehicles, handling and distribution of LP gas, and painting operations; nevertheless, emissions from diesel exhaust and asphalt operations showed differences, and the results suggest that these emissions could be underestimated.

PM2.5 Emission Elemental Composition from Diverse Combustion Sources in theMetropolitan Area of Mexico City

A field study was carried out from 2003 to 2004 with the aim to develop the PM2.5 emission source profiles from light-duty gasoline and heavy-duty diesel vehicles, as well as emission source profiles from waste incineration, wood burning, LP gas combustion, and meat broiling. Over 25 chemical species were quantified from the fine particles emitted by the different combustion sources investigated, including organic and elemental carbon, ions, and elements. The OC/TC ratio found in the different PM2.5 profiles was dissimilar as well as the sulfate, nitrate, ammonium, soil species, and trace element content. Consequently, these combustion emission profiles could be used in source reconciliation studies for fine particles.

Determination Of Volatile Organic Compounds Source Profiles In Mexico City

The ozone standard is exceeded more than 300 days a year in Mexico City, therefore it is imperative to reduce the atmospheric concentrations of its precursors, NOx and VOC. There is no pollution standard index nor regulation for volatile organic compounds (VOCs) in Mexico City and the concentrations of these compounds are two orders of magnitude than those found in California. On the other hand, many individual components of VOC have been identified as hazardous air pollutants and thus require control. The Chemical Mass Balance (CMB) model has been used to determine the apportionment of the VOC sources. This model requires the profiles of each VOC emission sources. In this paper the dry cleaning, graphic arts, degreasing and painting operations, VOC source profiles are presented. In Mexico, this is the first time that these profiles are experimentally determined. The characterization of more than 100 compounds was carried out during several sampling periods in different sites of each source, using stainless steel SUMMA® canisters and subsequent analysis by gas chromatography with flame ionized detector. It was found that some species are characteristic for each source profile, although the standard deviations were high for the different sites of each source.

Finding Qualitative Patterns in Ozone Behavior

Air pollution is one of the most important environmental problems in urban areas, being extremely critical in Mexico City. The main air pollution problem that has been identified in Mexico City metropolitan area is the formation of photochemical smog, primarily ozone. This toxic gas can produce harmful effects on the populations health, especially childrens health. The study and developement of modeling methodologies that allow the capturing of time series behavior becomes an important task when it is intended to predict the future behavior of the system under study. This paper presents the Visual-FIR tool, a new platform for the Fuzzy Inductive Reasoning (FIR) methodology. FIR offers a model-based approach to modeling and predicting either univariate or multivariate time series. Visual-FIR is used in this research for long term prediction of maximum ozone concentration in the centre region of Mexico City metropolitan area.