Scavenging of atmospheric formaldehyde by wet precipitation

Despite the great importance that formaldehyde has in atmospheric photochemistry, few studies have been reported on rain water. In this paper, concentrations of HCHO in rain fractions within rain events are presented. Two sampling sites were chosen: one at Mexico City, a great polluted urban area, and the second at Rancho Viejo, a forested area under the meteorological influence of the city. The results show a general decrease during the early portion of the rain event. This seems to indicate that below-cloud scavenging is the most important mechanism while, from the small variations observed in the latter portion of the rainfall, it is possible to assume within-cloud scavenging as the predominant mechanism. Using the HCHO concentrations in rain water, the mixing ratios were estimated for the two sampling sites. The values were 0.68 ppb and 0.44 ppb at Mexico City and Rancho Viejo, respectively. Measurements at ground level in Mexico City gave a mean HCHO concentration in air of 24 ppb, much higher than the estimated mixing ratio. The high levels of HCHO found in ambient air and in rain water reflect anthropogenic emissions as the potential atmospheric sources.     

Measurements of formaldehyde and acetaldehyde in the atmosphere of Mexico City

Ambient levels of carbonyls were measured at the University of Mexico campus, Mexico City. Only formaldehyde and acetaldehyde were measured, since aldehydes with higher molecular weight were not detected. The most abundant aldehyde was formaldehyde, with an overall ratio CH3CHO/H2CO of 0.43. Maximum concentrations occurred for formaldehyde at 10:00 h while for acetaldehyde at 8:00 h. Comparing the concentration measured in this work with those in urban areas it was found that the formaldehyde and acetaldehyde levels in Mexico City are among the highest reported in the literature.     

Diurnal and seasonal trends in carbonyl levels in a semi-urban coastal site in the Gulf of Campeche,Mexico

Concentrations of formaldehyde, acetaldehyde, acetone, propionaldehyde and butyraldehyde were measured in a semi-urban coastal site in the Gulf of Campeche, Mexico, during the winter, summer and autumn seasons. Measurements were carried out from 10 February 2004 to 16 November 2004. Carbonyl compound levels showed pronounced diurnal and seasonal variations. Maximum concentrations occurred between 13:00 h and 16:00 h, when vehicular traffic and photochemical activity were intense, and during the summer (when there was greater solar radiation). Only acetone during the first campaign (winter) did not correlate with temperature; it showed an inverse diurnal pattern, with higher concentrations during the night, probably due to a local and temporal source. The low concentrations of the main carbonyls found in this study, compared with the values reported for other urban areas, seem to indicate that air quality is still satisfactory in Carmen City.     

Fluoride levels in well-water from a chronic arsenicism area of Northern Mexico

This paper reports on the concentrations and geographical relationships between fluoride and total arsenic in 129 water wells of the Región Lagunera, Mexico, where arsenic has caused severe health effects. Fluoride concentrations ranged from less than 0.5 to 3.7 mg liter(-1); 25 samples (19.4%) had levels above 1.5mg liter(-1), the current WHO and Mexican drinking water standard, whereas 45 (34.9%) had levels below 0.5 mg liter(-1). The range of total arsenic concentrations was 0.008-0.624 mg liter(-1) and 64 (50%) had levels above 0.050 mg liter(-1), the current WHO standard. A linear regression analysis of arsenic and fluoride concentrations showed a highly positive correlation (r = 0.774), consistent with their geographical distribution. The highest concentrations of both elements were found in the northeastern part of the Región, mostly corresponding to rural areas, whereas the lowest concentrations were found in the southwestern part of the Región, as well as in the cities of Torreón in the state of Coahuila, and Gómez Palacio and Lerdo in the state of Durango. In consequence, people exposed to high arsenic concentrations are also exposed to fluoride at levels above the drinking water standard. The possibility of interactions between both elements is also discussed.     

Measurements of carbonyls in a 13-story building

BACKGROUND, AIM AND SCOPE: Formaldehyde and acetaldehyde are emitted by many mobile and stationary sources and secondary aldehydes are intermediates in the photo-oxidation of organic compounds in the atmosphere. These aldehydes are emitted indoors by many materials such as furniture, carpets, heating and cooling systems, an by smoking. Carbonyls, mainly formaldehyde and acetaldehyde, have been studied because of their adverse health effects. In addition, formaldehyde is a suspected carcinogen. Therefore, the concentrations of formaldehyde and acetaldehyde were determined to assess the inhalation exposure doses to carbonyls for people who work in a 13-story building and in order to evaluate the cancer hazard. METHODS: Carbonyl compounds in indoor and outdoor air were measured at a 13-story building located in Mexico City. The mezzanine, fifth and tenth floors, and the third level-parking garage were selected for sampling. Samples were collected in two sampling periods, the first from April 20 to 29, 1998 and the second from December 1 to 20, 1998. Carbonyls were sampled by means of DNHP-coated cartridges at a flow rate of 1 l min(-1) from 9:00 to 19:00 hours, during 2-hour time intervals and analyzed by HPLC with hours, during 2-hour time intervals and analyzed by HPLC with UV/VIS detection. RESULTS: Mean carbonyl concentrations were highest in the 3rd level-parking garage, with the formaldehyde concentration being the highest ranging from 108 to 418 microg m(-3). In working areas, the highest carbonyl arithmetic mean concentrations (AM) were observed on the 5th floor. Acetone and formaldehyde concentrations were highest in April ranging from 161 to 348 microg m(-3) (AM = 226) and from 157 to 270 microg m(-3) (AM = 221), respectively. Propionaldehyde and butyraldehyde were present in smaller concentrations ranging from 2 to 25 and 1 to 28 microg m(-3), respectively, considering all the samples. Mean indoor/outdoor ratios of carbonyls ranged from 1.8 to 9.6. A reduction of inhalation exposure doses of 41% and 45% was observed in the fifth floor air after the air conditioning systems had been repaired. Formaldehyde and acetaldehyde concentrations were higher in smoking environments. CONCLUSION: Indoor carbonyl concentrations were significantly greater than outdoor concentrations. Tobacco smoke seems to be the main indoor source of formaldehyde. After the air conditioning system was maintained and repaired (as was recommended), an important reduction in the emission of formaldehyde and acetaldehyde was achieved on all floors, except for the 3rd level parking garage, thereby reducing the inhalation exposure doses. RECOMMENDATION: The results obtained in this research demonstrated that maintenance of air conditioning systems must be carried out regularly in order to avoid possible adverse effects on health. Additionally, it is mandatory that isolated smoking areas, with air extraction systems, be installed in every public building.     

Chemical characterization of extractable water soluble matter associated with PM10 from Mexico City during 2000

We report the chemical composition of PM10-associated water-soluble species in Mexico City during the second semester of 2000. PM10 samples were collected at four ambient air quality monitoring sites in Mexico City. We determined soluble ions (chloride, nitrate, sulfate, ammonium, sodium, potassium), ionizable transition metals (Zn, Fe, Ti, Pb, Mn, V, Ni, Cr, Cu) and soluble protein. The higher PM(10) levels were observed in Xalostoc (45-174 microg m(-3)) and the lowest in Pedregal (19-54 microg m(-3)). The highest SO2 average concentrations were observed in Tlalnepantla, NO2 in Merced and O3 and NO(x) in Pedregal. The concentration range of soluble sulfate was 6.7-7.9 and 19-25.5 microg m(-3) for ammonium, and 14.8-29.19 for soluble V and 3.2-7.7 ng m(-3) for Ni, suggesting a higher contribution of combustion sources. PM-associated soluble protein levels varied between 0.038 and 0.169 mg m(-3), representing a readily inhalable constituent that could contribute to adverse outcomes. The higher levels for most parameters studied were observed during the cold dry season, particularly in December. A richer content of soluble metals was observed when they were expressed by mass/mass units rather than by air volume units. Significant correlations between Ni-V, Ni-SO4(-2), V-SO4(-2), V-SO2, Ni-SO2 suggest the same type of emission source. The variable soluble metal and ion concentrations were strongly influenced by the seasonal meteoclimatic conditions and the differential contribution of emission sources. Our data support the idea that PM10 mass concentration by itself does not provide a clear understanding of a local PM air pollution problem.     

Vertical and diurnal characterization of volatile organic compounds in ambient air in urban areas

More than half of the world's population lives in cities, and their populations are rapidly increasing. Information on vertical and diurnal characterizations of volatile organic compounds (VOCs) in urban areas with heavy ambient air pollution can help further understand the impact of ambient VOCs on the local urban environment. This study characterized vertical and diurnal variations in VOCs at 2, 13, 32, 58, and 111 m during four daily time periods (7:00 to 9:00 a.m., 12:00 to 2:00 p.m., 5:00 to 7:00 p.m., and 11:00 p.m. to 1:00 a.m.) at the upwind of a high-rise building in downtown, Kaohsiung City, Taiwan. The study used gas chromatography-mass spectrometry to analyze air samples collected by silica-coated canisters. The vertical distributions of ambient VOC profiles showed that VOCs tended to decrease at greater heights. However, VOC levels were found to be higher at 13 m than at ground level at midnight from 11:00 p.m. to 1:00 a.m. and higher at 32 than 13 m between 7:00 and 9:00 a.m. These observations suggest that vertical dispersion and dilution of airborne pollutants could be jointly affected by local meteorological conditions and the proximity of pollution sources. The maximum concentration of VOCs was recorded during the morning rush hours from 7:00 to 9:00 a.m., followed by rush hours from 5:00 to 7:00 p.m., hours from 12:00 to 2:00 p.m., and hours from 11:00 p.m. to 1:00 a.m., indicating that the most VOC compounds in urban air originate from traffic and transportation emissions. The benzene-toluene-ethyl benzene-xylene (BTEX) source analysis shows that BTEX at all heights were mostly associated with vehicle transportation activities on the ground.     

Effect of liquefied petroleum gas on ozone formation in Guadalajara and Mexico City

Leakages of liquefied petroleum gas (LPG) are suspected to contribute greatly to ozone (O3) formation in Mexico City. We tested such a hypothesis by outdoor captive-air irradiation (CAI) experiments in the two largest Mexican metropolitan areas: Guadalajara (GMA) in 1997 and Mexico City (MCMA) in 2000. O3 was monitored in each city for 20 days (8:00 a.m.-6:00 p.m.) in smog chambers containing unaltered morning air or morning air enriched with either commercial LPG or LPG synthetic mixture 60/40 (propane and butane). Tested additions of both components were 35% (by volume) in GMA and 60% (by volume) in MCMA. The addition effects on O3 (max) were compared with effects from diluting LPG components or total nonmethane hydrocarbons (tNMHCs) by 50%. Diluting tNMHCs had the greatest absolute effect at both cities: it lowered O3 (max) by 24% in GMA and 55% in MCMA. Adding commercial LPG increased O3 (max) by 6% in GMA and 28% in MCMA; whereas adding LPG synthetic mixture 60/40 caused a similar increase in O3 (max), 4 and 21% in GMA and MCMA, respectively. Compared with dilution of tNMHCs, dilution of LPG-associated compounds had a smaller decreasing effect on O3 (max), only 4% in GMA and 15% in MCMA. These results show that commercial LPG and LPG synthetic mixture 60/40 affect O3 formation to a lesser extent than estimated previously.     

Decline of sacred fir (Abies religiosa) in a forest park south of Mexico City

Decline of sacred fir (Abies religiosa) trees in the high elevation forest park, Desierto de los Leones, located south of Mexico City, is described. Trees located in the windward zone (exposed to air masses from Mexico City) were the most severely affected, especially trees at the distal ends of ravines. Examination of tree growth rings indicated decreases in ring widths for the past 30 years. Polluted air from Mexico City may be an important causal factor in fir decline. Drought, due to excessive removal of soil water, insects, mites and pathogens, and poor forest management are possible contributing and interactive factors in fir decline.     

Total Volatile Organic Compounds in the Urban Environment of Delhi

ABSTRACT

Total volatile organic compounds (TVOCs) in the urban ambient environment of Delhi were monitored from November 1994 to June 1995 at 13 sites using an inexpensive and a manual-labor-intensive sample collection procedure in want of sophisticated equipment. The results of the study show appreciable levels of TVOCs in the ambient environment of Delhi. The amount of TVOCs in the ambient environment was found to vary between 3 and 42 ppmv and exhibited wide temporal and seasonal variations. On a diurnal cycle, TVOC levels mostly peaked at 9:00 a.m., which coincided with the peak traffic hour. TVOC buildup in the urban atmosphere has serious implications for air quality through the formation of highly toxic oxidants. The results of this preliminary study make out a strong case for a regular monitoring of TVOCs in the urban environment of Delhi.     

Effect of Liquefied Petroleum Gas on Ozone Formation in Guadalajara and Mexico City

Abstract

Leakages of liquefied petroleum gas (LPG) are suspected to contribute greatly to ozone (O₃) formation in Mexico City. We tested such a hypothesis by outdoor captive-air irradiation (CAI) experiments in the two largest Mexican metropolitan areas: Guadalajara (GMA) in 1997 and Mexico City (MCMA) in 2000. O₃ was monitored in each city for 20 days (8:00 a.m.–6:00 p.m.) in smog chambers containing unaltered morning air or morning air enriched with either commercial LPG or LPG synthetic mixture 60/40 (propane and butane). Tested additions of both components were 35% (by volume) in GMA and 60% (by volume) in MCMA. The addition effects on O₃ (max) were compared with effects from diluting LPG components or total nonmethane hydrocarbons (tNMHCs) by 50%. Diluting tNMHCs had the greatest absolute effect at both cities: it lowered O₃ (max) by 24% in GMA and 55% in MCMA. Adding commercial LPG increased O₃ (max) by 6% in GMA and 28% in MCMA; whereas adding LPG synthetic mixture 60/40 caused a similar increase in O₃ (max), 4 and 21% in GMA and MCMA, respectively. Compared with dilution of tNMHCs, dilution of LPG-associated compounds had a smaller decreasing effect on O₃ (max), only 4% in GMA and 15% in MCMA. These results show that commercial LPG and LPG synthetic mixture 60/40 affect O₃ formation to a lesser extent than estimated previously.     

Ultraviolet Irradiance over Mexico City

Abstract

This article compiles and analyzes information on the interaction of both ground-level ultraviolet radiation and anthropogenic ozone in the extremely polluted atmosphere of Mexico City. Simultaneous anthropogenic ozone and global flux (sun and sky) measurements were recorded in near ultraviolet radiation (295-385 nm) for a 30-month period (March 1990 to August 1992). Results reveal that under clear sky conditions, high concentrations of ozone (and presumably of other pollutants) impede UV-fluxes from reaching their maximum values. Furthermore, heavy cloud cover causes ozone concentrations to reach their minimum values together with UV-minimum fluxes. Seasonal variation in UV-irradiance is also discussed. Findings indicate that maximum UV-fluxes occur in spring and summer and that minimum values occur in autumn and winter. Significant daily local reductions in UV-fluxes (up to 50%) during afternoon hours in Mexico City can be attributed to air pollution. Finally, the growing incidence of rickets in children residing in the Mexico City metropolitan area may be related both to dietary deficiencies and to the UV-flux depletion on the ground.     

Reduction of atmospheric emissions due to switching from fuel oil to natural gas at a power plant in a critical area in Central Mexico

ABSTRACT

A case study was conducted to evaluate the SO₂ emission reduction in a power plant in Central Mexico, as a result of the shifting of fuel oil to natural gas. Emissions of criteria pollutants, greenhouse gases, organic and inorganic toxics were estimated based on a 2010 report of hourly fuel oil consumption at the “Francisco Pérez Ríos” power plant in Tula, Mexico. For SO₂, the dispersion of these emissions was assessed with the CALPUFF dispersion model. Emissions reductions of > 99% for SO₂, PM and Pb, as well as reductions >50% for organic and inorganic toxics were observed when simulating the use of natural gas. Maximum annual (993 µg/m³) and monthly average SO₂ concentrations were simulated during the cold-dry period (152–1063 µg/m³), and warm-dry period (239–432 µg/m³). Dispersion model results and those from Mexico City’s air quality forecasting system showed that SO₂ emissions from the power plant affect the north of Mexico City in the cold-dry period. The evaluation of model estimates with 24 hr SO₂ measured concentrations at Tepeji del Rio suggests that the combination of observations and dispersion models are useful in assessing the reduction of SO₂ emissions due to shifting in fuels. Being SO₂ a major precursor of acid rain, high transported sulfate concentrations are of concern and low pH values have been reported in the south of Mexico City, indicating that secondary SO₂ products emitted in the power plant can be transported to Mexico City under specific atmospheric conditions.

Implications: Although the surroundings of a power plant located north of Mexico City receives most of the direct SO₂ impact from fuel oil emissions, the plume is dispersed and advected to the Mexico City metropolitan area, where its secondary products may cause acid rain. The use of cleaner fuels may assure significant SO₂ reductions in the plant emissions and consequent acid rain presence in nearby populated cities and should be compulsory in critical areas to comply with annual emission limits and health standards.     

Carbonyls in the metropolitan area of Mexico City: calculation of the total photolytic rate constants Kp(s(-1)) and photolytic lifetime (tau) of ambient formaldehyde and acetaldehyde

A great number of studies on the ambient levels of formaldehyde and other carbonyls in the urban rural and maritime atmospheres have been published because of their chemical and toxicological characteristics, and adverse health effects. Due to their toxicological effects, it was considered necessary to measure these compounds at different sites in the metropolitan area of Mexico City, and to calculate the total rate of photolytic constants and the photolytic lifetime of formaldehyde and acetaldehyde. Four sites were chosen. Sampling was carried out at different seasons and atmospheric conditions. The results indicated that formaldehyde was the most abundant carbonyl, followed by acetone and acetaldehyde. Data sets obtained from the 4 sites were chosen to calculate the total rate of photolysis and the photolytic lifetime for formaldehyde and acetaldehyde. Maximum photolytic rate values were obtained at the maximum actinic fluxes, as was to be expected.     

An air pollution modeling study using three surface coverings near the New International Airport of Mexico City

The dry lakebed of what once was the lake of Texcoco is the location selected for the New International Airport of Mexico City. This project will generate an important urban development near the airport with regional implications on air quality. Using a prognostic air quality model, the consequences of photochemical air pollution in the metropolitan area of Mexico City resulting from three possible coverings for the areas of the lakebed that are not occupied by the runway and terminal building are investigated. These coverings are desert, grassland, and water and occupy an area of 63 km2. This study is based on a representative high pollution episode. In addition to reducing the emission of primary natural particles, the water covering generates a land-water breeze capable of maintaining enough ventilation to reduce pollutant concentrations over a localized region of the metropolitan area and may enhance the wind speed on the coasts of the proposed lake.     

Carbon Monoxide Trend,Meteorology, and Three-Way Catalysts in Mexico City

ABSTRACT

From the analysis of data of the Inspection/Maintenance (I/M) program, and of the long-term trend of ambient CO concentrations in Mexico City, it is inferred that three-way catalysts (TWCs) have a 45% efficiency, well below the expected 90% value. The most probable causes are sulfur poisoning, lead contamination, and ceramic breakage due to bumps and potholes on the streets. Also, we have found a ratio between the average daily peak value of atmospheric CO and gasoline consumption: (11 ± 1) ppbCO/MLm (million liters of gasoline per month) in 1988 decaying to (10 ±1) in 1991 for Mexico City before the introduction of TWCs. In addition, we found a correlation between the monthly averages of CO daily peak and meteorological variables, explaining most of the seasonal changes using only the intensity of the inversion layer and surface wind speed.     

The Valley of Mexico: summary of observational studies on its air quality and effects on vegetation

Present day Mexico City was established on the banks of the now dead Lake Texcoco by Aztec Indians in a.d. 1325. Over time, increasing population growth, urbanization, vehicular traffic and the number of diverse stationary sources, coupled with its topography and the resultant frequency of prevalent stagnant air masses make Mexico City one of the most polluted areas in the world. Use of biological indicator plants since the early 1970s has shown the critical nature of phytotoxic photochemical oxidants in the region. More recent empirical studies with bean, soybean and pine species confirm these observations and raise concern regarding the geographic magnitude of the problem. Surface measurements of air quality in the region are inadequate and require much additional support. Ultimately, ambient air quality measurements must be coupled with the observations on responses of sensitive vegetation. While the results presented in this paper are primarily observational or qualitative, they hopefully serve the purpose of bringing attention to a critical air quality issue in a developing country.     

Ozone exposure among Mexico City outdoor workers

In researching health effects of air pollution, pollutant levels from fixed-site monitors are commonly assigned to the subjects. However, these concentrations may not reflect the exposure these individuals actually experience. A previous study of ozone (O3) exposure and lung function among shoe-cleaners working in central Mexico City used fixed-site measurements from a monitoring station near the outdoor work sites as surrogates for personal exposure. The present study assesses the degree to which these estimates represented individual exposures. In 1996, personal O3 exposures of 39 shoe-cleaners working outdoors were measured using an active integrated personal sampler. Using mixed models, we assessed the relationship between measured personal O3 exposure and ambient O3 measurements from the fixed-site monitoring station. Ambient concentrations were approximately 50 parts per billion higher, on average, than personal exposures. The association between personal and ambient O3 was highly significant (mixed model slope p < 0.0001). The personal/ambient ratio was not constant, so use of the outdoor monitor would not be appropriate to rank O3 exposure and evaluate health effects between workers. However, the strong within-worker longitudinal association validates previous findings associating day-to-day changes in fixed-site O3 levels with adverse health effects among these shoe-cleaners and suggests fixed-site O3 monitors may adequately estimate exposure for other repeated-measure health studies of outdoor workers.     

Impact of wildfires on the air quality of Mexico City, 1992-1999

Wildfires in Mexico increased in 1998, compared to information for the last 6 years. The average number of wildfires in the Mexico City Metropolitan Area (MCMA) for this year (1998) were 58% (1916 events) more events than the 1992-1997 (average cases 1217 events). Mexico City affected area corresponds to 1.3% of the national affected area. The purpose of this paper is to evaluate the impact on the particles air quality due to the wildfire emissions at the MCMA and surrounding areas. Using the corresponding US EPA emission factors for wildfires, the tons of particulate matter, nitrogen oxides, carbon monoxide, and total hydrocarbons emitted by this source for the MCMA case were obtained. The calculated emissions during wildfires were correlated with the levels of particles present in the atmosphere. A comparison of the concentration levels of particles, both as PM10 as well as TSP, were made for the years 1992-1998, during wet and dry season, being March, April, and May the critical months due to the presence of wildfires. A good correlation is observed between particulate wildfire emissions and particulate air quality, being stronger for TSP. A clear impact on the particles air quality due to the increase of wildfires in 1998, is observed when this year is compared with 1997, presenting an increment of 200-300% for some monitoring stations.     

An Air Pollution Modeling Study Using Three Surface Coverings Near the New International Airport of Mexico City

Abstract

The dry lakebed of what once was the lake of Texcoco is the location selected for the New International Airport of Mexico City. This project will generate an important urban development near the airport with regional implications on air quality. Using a prognostic air quality model, the consequences of photochemical air pollution in the metropolitan area of Mexico City resulting from three possible coverings for the areas of the lakebed that are not occupied by the runway and terminal building are investigated. These coverings are desert, grassland, and water and occupy an area of 63 km². This study is based on a representative high pollution episode. In addition to reducing the emission of primary natural particles, the water covering generates a land-water breeze capable of maintaining enough ventilation to reduce pollutant concentrations over a localized region of the metropolitan area and may enhance the wind speed on the coasts of the proposed lake.