Presence of aliphatic and polycyclic aromatic hydrocarbons in the atmosphere of Northwestern Mexico City, Mexico (original) (raw)
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Environmental Pollution, 1999
Total suspended particles (TSP), particulate-(ALIp) and semi-volatile aliphatic hydrocarbons (ALIsv) were measured in air sampled during the day and night over 7±8 months in industrial, commercial and residential sectors of La Plata, Argentina. TSP, ALIp and ALIsv ranges were 23±219 mg/m 3 , 11±447 and 12±719 ng/m 3 , respectively. Maximum values were recorded at a downtown site whereas the residential station showed lower levels. Concentrations were usually higher during the day and during fall and winter. Two-and three-way ANOVA were performed to evaluate the day-night, inter-station, and inter-month variability. The amount of total variability accounted by these factors was 14, 25 and 23% (p < 0.01) for TSP; 0.8, 11 and 39% (p < 0.03) for ALIp; and 0.6, 7.9 and 15% (p < 0.3) for ALIsv, respectively. Overall, the inter-month variability prevailed; inter-station dierences were most signi®cant in the summer when the day-night variability was lower. For the particulate phase, the day-night dierences were more signi®cant at the downtown and residential sites. The composition of ALIp and ALIsv re¯ected the contribution from biogenic long chain odd n-alkanes and petrogenic lower molecular weight n-alkanes. Plant cuticular waxes accounted for 34±96% of ALIp with higher values during the summer and at the Residential station. A principal component analysis clearly discriminated ALIsv, almost entirely derived from exhaust and diesel fuel emissions, from ALIp composed of mixed biogenic-petrogenic sources. The lowest day-night dierences observed during the summer were related to a higher proportion of biogenic``natural'' material during this period of full plant grow and lower vehicle circulation. The larger day-night dierences registered at the downtown station were related to an enhanced input of anthropic sources (vehicles, fossil fuels, lubricating oils) during the most active day period.
Sources and transformations of particle-bound polycyclic aromatic hydrocarbons in Mexico City
Atmospheric Chemistry and Physics, 2006
Understanding sources, concentrations, and transformations of polycyclic aromatic hydrocarbons (PAHs) in the atmosphere is important because of their potent mutagenicity and carcinogenicity. The measurement of particlebound PAHs by three different methods during the Mexico City Metropolitan Area field campaign in April 2003 presents a unique opportunity for characterization of these compounds and intercomparison of the methods. The three methods are (1) collection and analysis of bulk samples for time-integrated gas-and particle-phase speciation by gas chromatography/mass spectrometry; (2) aerosol photoionization for fast detection of PAHs on particles' surfaces; and (3) aerosol mass spectrometry for fast analysis of size and chemical composition. This research represents the first time aerosol mass spectrometry has been used to measure ambient PAH concentrations and the first time that fast, real-time methods have been used to quantify PAHs alongside traditional filter-based measurements in an extended field campaign. Speciated PAH measurements suggest that motor vehicles and garbage and wood burning are important sources in Mexico City. The diurnal concentration patterns captured by aerosol photoionization and aerosol mass spectrometry are generally consistent. Ambient concentrations of particlephase PAHs typically peak at ∼110 ng m −3 during the morning rush hour and rapidly decay due to changes in source activity patterns and dilution as the boundary layer rises, although surface-bound PAH concentrations decay faster. The more rapid decrease in surface versus bulk PAH concentra-Correspondence to: L. C. Marr (lmarr@vt.edu) tions during the late morning suggests that freshly emitted combustion-related particles are quickly coated by secondary aerosol material in Mexico City's atmosphere and may also be transformed by heterogeneous reactions.
Journal of the Air & Waste Management Association, 2007
This paper presents the results of the first reported study on fine particulate matter (PM) chemical composition at Salamanca, a highly industrialized urban area of Central Mexico. Samples were collected at six sites within the urban area during February and March 2003. Several trace elements, organic carbon (OC), elemental carbon (EC), and six ions were analyzed to characterize aerosols. Average concentrations of PM with aerodynamic diameter of less than 10 m (PM 10) and fine PM with aerodynamic diameter of less than 2.5 m (PM 2.5) ranged from 32.2 to 76.6 g m Ϫ3 and 11.1 to 23.7 g m Ϫ3 , respectively. OC (34%), SO 4 ϭ (25.1%), EC (12.9%), and geological material (12.5%) were the major components of PM 2.5. For PM 10 , geological material (57.9%), OC (17.3%), and SO 4 ϭ (9.7%) were the major components. Coarse fraction (PM 10 Ϫ PM 2.5), geological material (81.7%), and OC (8.6%) were the dominant species, which amounted to 90.4%. Correlation analysis showed that sulfate in PM 2.5 was present as ammonium sulfate. Sulfate showed a significant spatial variation with higher concentrations to the north resulting from predominantly southwesterly winds above the surface layer and by major SO 2 sources that include a power plant and refinery. At the urban site of Cruz Roja it was observed that PM 2.5 mass concentrations were similar to the submicron fraction concentrations. Furthermore, the correlation between EC in PM 2.5 and EC measured from an aethalometer was r 2 ϭ 0.710. Temporal variations of SO 2 and nitrogen oxide were observed during a day when the maximum concentration of PM 2.5 was measured, which was associated with emissions from the nearby refinery and power plant. From cascade impactor measurements, the three measured modes of airborne particles corresponded with diameters of 0.32, 1.8, and 5.6 m.
RESUME OF THE BOOK “FUNDAMENTAL OF AIR POLLUTION FOURTH EDITION” AUTHORS : DANIEL A. VALLERO
The principal requirement of a sampling system is to obtain a sample that is representative of the atmosphere at a particular place and time and that can be evaluated as a mass or volume concentration. The sampling system should not alter the chemical or physical characteristics of the sample in an undesirable manner. The major components of most sampling systems are an inlet manifold, an air mover, a collection medium, and a flow measurement device. One example is sampling for SO2. Liquid sorbents for SO2 depend on the solubility of SO 2 in the liquid collection medium. Certain liquids at the correct pH are capable of removing ambient concentrations of SO2 with 100% efficiency until the characteristics of the solution are altered so that no more SO2 may be dissolved in the volume of liquid provided. Under these circumstances, sampling is 100% efficient for a limited total mass of SO2 transferred to the solution, and the technique is acceptable as long as sampling does not continue beyond the time that the sampling solution is saturated. A second example is the use of solid sorbents such as Tenax for volatile hydrocarbons by the physical adsorption of the individual hydrocarbon molecules on active sites of the sorbent. Collection efficiency drops drastically when the active sites become saturated.
Atmospheric Environment, 2005
Atmospheric processes governing the fate of the polycyclic aromatic hydrocarbons (PAHs) in the atmosphere of the Eastern Mediterranean were studied for a two-year period (2000-2001). Atmospheric samples were collected off-shore over the Eastern Mediterranean Sea as well as at a background station in Northeastern Crete, Greece. PAH total concentration varied from 4.1 to 57.2 ng m(-3), with &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;90% in the gas phase. Gas-to-particle distribution of PAHs was correlated (R2 0.75-0.98, p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.001) with their subcooled vapor pressure. Seasonal changes in the total concentration of PAHs were not observed, while the origin of air mass was the dominant factor determining their atmospheric concentration levels. Air masses, originating from central and eastern Europe, were associated with the highest PAH concentrations. Gas-to-particle distribution of sigmaPAHs correlated well (R2 0.75-0.98, p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.001) with their subcooled vapor pressure. Tropospheric ozone concentration correlated with the vapor-phase PAH concentration (p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.001) but less (p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.01) with the particulate PAH concentration. Distribution of volatile PAHs over the Eastern Mediterranean basin was uniform. Conversely, particulate PAH concentrations were higher at sampling sites located close to urban centers. Calculated relative removal rates of PAHs associated with particles were significantly higher than those of volatile members.
Mexico City air quality: a qualitative review of gas and aerosol measurements (1960–2000)
Atmospheric Environment, 2001
Mexico City, one of the largest cities in the world, has a major problem with high levels of anthropogenic gases and aerosols. Some facets of this problem have been studied through measurements made during the past 40 years. These measurements are reviewed and evaluated with respect to physical processes that underlie the primary and secondary formation of gases and aerosols, their spatial and temporal evolution as well as their potential impact on the local and regional environment. Past measurements are heavily biased towards certain locations and time periods, and are of limited use for understanding fundamental processes that govern the formation and evolution of the principal pollutants. Recommendations are made whereby the measurement database could be expanded to better represent the characteristics of Mexico City gases and aerosols and to contribute to mitigation strategies that would lessen the environmental impact of these pollutants.
Organic Compound in Airborne Particles and their Genottoxic Effects in Mexico City
Air Quality Monitoring, Assessment and Management, 2011
Aerosol is constituted by a mixture of gases and suspended particles (liquid and solid). However, the particulate phase is commonly referred to as aerosol. Aerosols have been considered to play a significant role in atmospheric chemistry physical processes, meteorology and climate change, justifying in all cases the impact on humans. Their study will add to the knowledge regarding their transport and atmospheric processes, their spatial and temporal behavior and their impact on materials, visibility, climate and human health. In this sense, the particle phase of an aerosol, called airborne particles, is of relevance to www.intechopen.com Air Quality Monitoring, Assessment and Management 346 public health due to their proven morbidity and mortality effects on humans (Pope & Dockery, 2006). The magnitude of these effects generally depends upon their seasonal behavior, sources, chemical composition, number, mass, surface area and size, which increases the human health risk when the particles are inhaled because particle size is inversely proportional to the deep deposition area in the respiratory system (Sugita et al., 2004). An essential step is to measure these variables which may all be important physicalchemical properties that influence particle toxicology (Sen et al., 2007). The risk to human health is related with a long period of exposure to environmental pollutants, which increases in children and elderly persons. Human exposure to particles for both a short-and a long-term has been associated with measures of genetic damage (Lewtas, 2007). Airborne particles can be generated through grinding activities, soil resuspension due to wind or other natural processes as soil erosion, or they can be a product of the incomplete combustion of fossil and non-fossil materials as well as a result of chemical reactions and condensation onto preexistent particles (Solomon et al., 2001). Their chemical composition is a complex mixture that depends upon several factors as emission sources, geographic and climatic conditions, atmospheric reactivity, and the like. The main process of aerosol production in nature and the most important mass-transfer via gas-phase and particle-phase is by condensation, through a supersaturated vapor initiated by the presence of small particles (heterogeneous or homogeneous nucleation) or ions that serve as sites for particle formation (Hinds, 1999). Micrometer-sized particles are strongly attached to any surface they contact through the London-van der Waals forces-, which is one of the most important adhesive forces to form aggregates (Hinds, 1999). Particle size, density and shape are some of the physical properties that influence pulmonary deposition, ground deposition rate, aging during atmospheric transport and residence time in the air. These properties help identify emission sources and /or the atmospheric formation process. Size, which ranges from 10 nm to 100 µm and is commonly analyzed by lognormal distributions, is one of the most important physical properties of the particles. It is measured in terms of the aerodynamic diameter defined as the equivalent spherical particle diameter that has a density of 1 g cm-3 with the same settling velocity as the target particle, and it is used for characterizing filtration, respiratory deposition and the performance of many types of air cleaners and air particle samplers. 3. Organic aerosol 3.1 Impact on climate and air quality Aerosol particles influence the Earth's radiative and hydrological balance (Ramanathan et al., 2001). Knowledge of their contribution to radiative forcing is still uncertain (IPCC, 2007). Soot particles, which are aggregated carbonaceous spherules of tens of nanometers in size, and which have graphitic structures, are emitted from incomplete combustion of fossil fuel, biofuel, and biomass carbon together with organic matter. Soot particles contribute to the warming effect in the atmosphere through absorption of sunlight (Bong & Bergstrom, 2006). Black carbon is found throughout the atmosphere, and it is thought to be the most important component to aerosol absorption of solar radiation although attention has recently turned to "brown" organic carbon (Sun et al., 2007) as a source of significant absorption, particularly in the near-UV. The scattering and absorption of incoming solar radiation is also affected by the organic aerosol component (Jacobson et al., 2000). Organics can alter the hygroscopicity www.intechopen.com Organic Compounds in Airborne Particles and their Genotoxic Effects in Mexico City 347 of the particles (Thomas et al., 1999), and this changes the radiative forcing that involves cloud condensation and nuclei formation; such forcing may have opposite signs depending on the type of particulate carbon (NRC, 1996). Emissions of organic species have the potential to influence aerosol-cold cloud interactions and climate (Cziczo et al., 2004). The hygroscopicity of atmospheric aerosols has a considerable effect on particle size and therefore on visibility (Vasconcelos et al., 1994). Dissolved and surface-active organic compounds in droplets and aerosols affect the albedo of clouds and rain development (Facchini et al., 1999). Size distributions as well as the optical and hydrophilic properties of organic particles are also uncertain due to the lack of data (Liousse et al., 2005), in part owing to the complexity of the organic content which may involve several hundreds of compounds of a different chemical class and which have different biological effects. Although biological particles such as spores, bacteria, algae, pollen, vegetation and insect debris, animal cell fragments, and the like (Winiwater et al., 2009) can be considered as part of the particle organic fraction, their discussion goes beyond this chapter.