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A significant proportion of the solar irradiance that reaches the Earth's surface is normally attenuated by atmospheric properties and overcast conditions related to the rainy season. The Solar Analyst (SA) model, irradiance and long term precipitation data were used to assess this relationship in Guadalajara, Mexico. A spatial analysis based on morphological and statistical criteria increased the model's certainty. The SA model explains 95.4% of the irradiation variability observed on the ground, with average uncertainties of 3.7% during clear sky conditions in the dry season and 4.4% on sunny days in the wet season. The meteorological data analysis shows that total precipitation in 2014 had an atypical temporal distribution and was slightly lower (12.6%) than the average from 1991 to 2012. A deficit of 39% in precipitation compared to the long term average was found in the first half of the season, which was later partially compensated. This deficit was interpreted as a temporary delay in high values of precipitation. Based on the potential average irradiation from the SA model and field observations, it can be concluded that overcast conditions related to rainfall through 2014 attenuated approximately 28.5% of the incoming solar energy. Taking the global energy balance into account, this fraction was higher in comparison to the energy proportion reflected by the cloud's albedo (ca 23%). These results suggest that both the high proportion of energy attenuated and atypical weather conditions may be local effects of large-scale phenomena such as the El Niño-Southern Oscillation.

Polycyclic aromatic hydrocarbons (PAHs) and quinones in the gas phase and as submicron particles raise concerns due to their potentially carcinogenic and mutagenic properties. The majority of existing studies have investigated the formation of quinones, but it is also important to consider both the primary and secondary sources to estimate their contributions. The objectives of this study were to characterize PAHs and quinones in the gas and particulate matter (PM 1 ) phases in order to identify phase distributions, sources, and cancer risk at two urban monitoring sites in the Guadalajara Metropolitan Area (GMA) in Mexico. The simultaneous gas and PM 1 phases samples were analyzed using a gas chromatography-mass spectrometer. The lifetime lung cancer risk (LCR) due to PAH exposure was calculated to be 1.7 × 10 −3 , higher than the recommended risk value of 10 −6 , indicating a potential health hazard. Correlations between parent PAHs, criteria pollutants, and meteorological parameters suggest that primary sources are the main contributors to the Σ 8 Quinones concentrations in PM 1 , while the secondary formation of 5,12-naphthacenequinone and 9,10-anthraquinone may contribute less to the observed concentration of quinones. Additionally, naphthalene, acenaphthene, fluorene, phenanthrene, and anthracene in PM 1 , suggest photochemical degradation into unidentified species. Further research is needed to determine how these compounds are formed.

In recent years, the interest in aerosol particles has increased due to concerns about the effects on human health. The study of the chemical characterization (organic matter, sulfates, nitrates, and black carbon) has improved the knowledge about the negative contribution of chemicals to the environment. The identification of secondary processes (from pollutants such as SO 2 , NO x , and PAHs) and their role when combined with environmental factors such as humidity, solar radiation, and temperature are also of interest. With this background, this chapter seeks to highlight the most recent findings on the chemical composition of aerosol particles in the ambient air of one of the main cities of Mexico: the Metropolitan Area of Guadalajara. This megalopolis has almost 60% of the population of the Jalisco state, approximately 2.2 million vehicles and an extensive artisan brick production. Furthermore, due to its geographical position, it experiences frequent episodes of thermal inversion and exposition to high levels of solar radiation, mainly during the first half of the year.

The spatial assessments of water supply quality from wells, springs, and surface bodies were performed during the dry and rainy seasons in six municipalities in the eastern regions of Michoacán (Central Mexico). Different physicochemical parameters were used to determine the supplies’ Water Quality Index (WQI); all of the communities presented good quality. The analysis indicates that many water quality parameters were within limits set by the international standards, showing levels of “excellent and good quality” according to WQI, mainly during the dry season (except at San Pedro Jácuaro and Irimbo communities in the rainy season). However, some sites showed “poor quality” and “unsuitable drinking water” related to low pH levels (<5) and high levels of turbidity, color, Fe, Al, Mn, and arsenic. Multivariate statistical analysis techniques (Principal Component and Hierarchical Cluster) and geographic information system (GIS) identify potential sources of water pollution and estimate the geographic extension of parameters with negative effects on human health (mainly in communities without sampling). According to multivariate analysis, the Na+/K+ ratio and water temperature (22–42 °C) in various sites suggest that the WQI values were affected by geological and geothermal conditions and physical changes between seasons, but were not from anthropogenic activity. The GIS established predictions about the probable spatial distribution of arsenic levels, pH, temperature, acidity, and hardness in the study area, which provides valuable information on these parameters in the communities where the sampling was not carried out. The health risk assessment for dermal contact and ingestion showed that the noncancer risk level exceeded the recommended criteria (HQ > 1) in the rainy season for three target groups. At the same time, the carcinogenic risk (1 × 10−3) exceeded the acceptability criterion in the rainy season, which suggests that the As mainly represents a threat to the health of adults, children, and infants.

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The diel variation of meteorological conditions strongly influences the formation processes of secondary air pollutants. However, due to the complexity of sampling highly reactive chemical compounds, significant information about their transformation and source can be lost when sampling over long periods, affecting the representativeness of the samples. In order to determine the contribution of primary and secondary sources to ambient levels of polyaromatic hydrocarbons (PAHs) and quinones, measurements of gas and PM1 phases were conducted at an urban site in the Guadalajara Metropolitan Area (GMA) using a 4-h sampling protocol. The relation between PAHs, quinones, criteria pollutants, and meteorology was also addressed using statistical analyses. Total PAHs (gas phase + PM1 phase) ambient levels ranged between 184.03 ng m−3 from 19:00 to 23:00 h and 607.90 ng m−3 from 07:00 to 11:00 h. These figures both coincide with the highest vehicular activity peak in the morning and at night near the sampling site, highlighting the dominant role of vehicular emissions on PAHs levels. For the gas phase, PAHs ranged from 177.59 to 595.03 ng m−3, while for PM1, they ranged between 4.81 and 17.44 ng m−3. The distribution of the different PAHs compounds between the gas and PM1 phases was consistent with their vapour pressure (p °L) reported in the literature, the PAHs with vapour pressure ≤ 1 × 10−3 Pa were partitioned to the PM1, and PAHs with vapour pressures ≥ 1 × 10−3 Pa were partitioned to the gas phase. PAHs diagnostic ratios confirmed an anthropogenic emission source, suggesting that incomplete gasoline and diesel combustion from motor vehicles represent the major share of primary emissions. Quinones ambient levels ranged between 18.02 ng m−3 at 19:00–23:00 h and 48.78 ng m−3 at 15:00–19:00 h, with significant increases during the daytime. The distribution of quinone species with vapour pressures (p °L) below 1 × 10−4 Pa were primarily partitioned to the PM1, and quinones with vapour pressures above 1 × 10−4 Pa were mainly partitioned to the gas phase. The analysis of the distribution of phases in quinones suggested emissions from primary sources and their consequent degradation in the gas phase, while quinones in PM1 showed mainly secondary formation modulated by UV, temperature, O3, and wind speed. The sampling protocol proposed in this study allowed obtaining detailed information on PAHs and quinone sources and their secondary processing to be compared to existing studies within the GMA.