Climate change and its consequences seem to be increasingly evident in our daily lives. However, is it possible for students to identify a relationship between these large-scale events and the chemistry taught in the classroom? The aim of the present work is to demonstrate that chemistry can assist in elucidating important environmental issues. Simple experiments are used to demonstrate the mechanism of cloud formation, as well as the influence of anthropogenic and natural emissions on the precipitation process. The experiments presented show the way in which particles of soluble salts commonly found in the environment can absorb water in the atmosphere and influence cloud formation.

Ambient aerosols were collected in an agro-industrial region of Sao Paulo State (Brazil) between May 2010 and February 2012 (n = 87). The atmosphere of the study region is highly affected by the emissions of gases and particles from sugar and fuel ethanol production, because part of the area planted with sugarcane is still burned before manual harvesting. This work proposes the quantification of total sugars as an alternative chemical tracer of biomass burning, instead of levoglucosan. The quantification of total sugars requires a small area of a filter sample and a simple spectrophotometer, in contrast to the determination of levoglucosan, which is much more complex and time-consuming. Total sugars concentrations in the aerosol ranged from 0.28 to 12.5 mu g m(-3), and (similarly to levoglucosan) the emissions were significantly higher at night and during the sugarcane harvest period, when most agricultural fires occur. The linear correlation between levoglucosan and total sugars (r = 0.612) was stronger than between levoglucosan and potassium (r = 0379), which has previously been used as a biomass burning tracer. In the study region, potassium is used in fertilizers, and this, together with substantial soil dust resuspension, makes potassium unsuitable for use as a tracer. On average, ca. 40% of the total sugars was found in particles smaller than 0.49 mu m. By including data from previous work, it was possible to identify from 35 to 42% of the total sugars, with biomass burning making the largest contribution. The high solubility in water of these sugars means that determination of their concentrations could also provide important information concerning the hydrophilic properties of atmospheric aerosols. (C) 2014 Elsevier Ltd. All rights reserved.

This work presents the first comprehensive organic characterization of atmospheric aerosols from an agro-industrial region (São Paulo State, Brazil) highly impacted by biomass burning. The organic speciation was performed using different solvents of increasing polarity, enabling the identification and quantification of 172 different organic species by GC–MS. The mass of organic compounds reached 123μgm−3 in an aerosol sample collected during the sugar cane harvest period compared with 0.82μgm−3 in the non-harvest period. The samples most impacted by biomass burning were those with the highest percentages of non-polar compounds (n-alkanes; up to 96%). However, in absolute terms, the total mass of polar compounds in such samples was greater than for samples less impacted by this activity. Retene (a marker for biomass combustion) was the most abundant of the 19 polycyclic aromatic hydrocarbons quantified, corresponding to 14%–84%. This work shows that biomass burning was responsible for a benzo(a)pyrene equivalent index value that exceeded the recommendation of the World Health Organization. Principal component analysis indicated that agricultural biomass burning and emissions from crop processing facilities explained 42% of the variance of the data, while 37% was explained by urban emissions, 10% by vehicle emissions, and 10% by biogenic sources. This study provides insights into the emissions of a suite of organic compounds that could participate in anthropic alteration of regional cloud formation and precipitation patterns.

This work aimed to better understand how aerosol particles from sugar cane burning contribute to the chemical composition of the lower troposphere in an agro-industrial region of Sao Paulo State (Brazil) affected by sugar and ethanol fuel production. During a period of 21 months, we collected 105 samples and quantified 20 saccharides by GC-MS. The average concentrations of levoglucosan (L), mannosan (M), and galactosan (G) for 24-h sampling were 116, 16, and 11 ng m(-3) respectively. The three anhydrosugars had higher and more variable concentrations in the nighttime and during the sugar cane harvest period, due to more intense biomass burning practices. The calculated L/M ratio, which may serve as a signature for sugar cane smoke particles, was 9 +/- 5. Although the total concentrations of the anhydrosugars varied greatly among samples, the relative mass size distributions of the saccharides were reasonably constant. Emissions due to biomass burning were estimated to correspond to 69% (mass) of the sugars quantified in the harvest samples, whereas biogenic emissions corresponded to 10%. In the non-harvest period, these values were 44 and 27%, respectively, indicating that biomass burning is an important source of aerosol to the regional atmosphere during the whole year. (C) 2014 Elsevier Ltd. All rights reserved.

Polycyclic aromatic hydrocarbons (PAHs), nitro-PAHs, and oxy-PAHs were studied in the atmospheric particulate matter of a subtropical rural region (São Paulo State, Brazil) affected by emissions from sugar cane burning. Diurnal and nocturnal samples were collected from May to June of 2010. In general, average PAH concentrations were significantly higher at night, suggesting that the compounds were predominantly emitted to the atmosphere during biomass burning (which was mainly performed at night). The maximum average PAH concentration was found for benzo[b]fluoranthene at night (2.9 ± 5.4 ng m−3). Among the nitro-PAH compounds, the highest average concentrations were obtained for 9-nitrophenanthrene in diurnal and nocturnal samples (1.5 ± 1.2 and 1.3 ± 2.1 ng m−3, respectively). In contrast to the PAH and nitro-PAH compounds, the oxy-PAHs could not be directly associated with sugar cane burning. The most abundant oxy-PAH compound was benzanthrone (1.6 ± 1.3 ng m−3) at night, followed by 9,10-anthraquinone (1.1 ± 0.9 ng m−3) and 9-fluorenone (0.4 ± 0.1 ng m−3) during the day.

Strong diurnal cycles in ambient aerosol mass were observed in a rural region of Southeast Brazil where the trace composition of the lower troposphere is governed mainly by emissions from agro-industry. An optical particle counter was used to record size-segregated aerosol number concentrations between 13 May 2010 and 15 March 2011. The data were collected every 10min and used to calculate aerosol mass concentrations. Aerosol samples were also collected onto filters during daytime (10:00-16:00 local time) and nighttime (20:00-06:00) periods, for subsequent analysis of soluble ions and water-soluble organic carbon. Biomass burning aerosols predominated during the dry winter, while secondary aerosols were most important in the summer rainy season. In both seasons, diurnal cycles in calculated aerosol mass concentrations were due to the uptake of water by the aerosols and, to a lesser extent, to emissions and secondary aerosol formation. In neither season could the observed mass changes be explained by changes in the depth of the boundary layer. In the summer, nighttime increases in aerosol mass ranged from 2.7-fold to 81-fold, depending on particle size, while in the winter, the range was narrower, from 2.2-fold to 9.5-fold, supporting the possibility that the presence of particles derived from biomass burning reduced the overall ability of the aerosols to absorb water.

Increased reactive nitrogen (Nr) deposition due to expansion of agro-industry was investigated considering emission sources, atmospheric transport and chemical reactions. Measurements of the main inorganic nitrogen species (NO2, NH3, HNO3, and aerosol nitrate and ammonium) were made over a period of one year at six sites distributed across an area of ∼130,000 km2 in southeast Brazil. Oxidized species were estimated to account for ∼90% of dry deposited Nr, due to the region’s large emissions of nitrogen oxides from biomass burning and road transport. NO2-N was important closer to urban areas, however overall HNO3-N represented the largest component of dry deposited Nr. A simple mathematical modeling procedure was developed to enable estimates of total Nr dry deposition to be made from knowledge of NO2 concentrations. The technique, whose accuracy here ranged from <1% to 29%, provides a useful new tool for the mapping of reactive nitrogen deposition.

Direct‐sampling and remote‐sensing measurements were made at the crater rim of Masaya volcano (Nicaragua) to sample the aerosol plume emanating from the active vent. We report the first measurements of the size distribution of fine silicate particles (d < 10 μm) in Masaya's plume, by automated scanning electron microscopy (QEMSCAN) analysis of a particle filter. The particle size distribution was approximately lognormal with modal d ∼ 1.15 μm. The majority of these particles were found to be spherical. These particles are interpreted to be droplets of quenched magma produced by a spattering process. Compositional analyses confirm earlier reports that the fine silicate particles show a range of compositions between that of the degassing magma and nearly pure silica and that the extent of compositional variability decreases with increasing particle size. These results indicate that fine silicate particles are altered owing to reactions with acidic droplets in the plume. The emission flux of fine silicate particles was estimated as ∼1011 s−1, equivalent to ∼55 kg d−1. Sun photometry, aerosol spectrometry, and thermal precipitation were used to determine the overall particle size distribution of the plume (0.01 < d(μm) < 10). Sun photometry and aerosol spectrometry measurements indicate the presence of a large number of particles (assumed to be aqueous) with d ∼ 1 μm. Aerosol spectrometry measurements further show an increase in particle size as the nighttime approached. The emission flux of particles from Masaya was estimated as ∼1017 s−1, equivalent to ∼5.5 Mg d−1 where d < 4 μm.

Particle size distributions for soluble and insoluble species in Mt. Etna's summit plumes were measured across an extended size range (10 nm < d < 100 μm) using a combination of techniques. Automated scanning electron microscopy (QEMSCAN) was used to chemically analyze many thousands of insoluble particles (collected on pumped filters) allowing the relationships between particle size, shape, and composition to be investigated. The size distribution of fine silicate particles (d < 10 μm) was found to be lognormal, consistent with formation by bursting of gas bubbles at the surface of the magma. The compositions of fine silicate particles were found to vary between magmatic and nearly pure silica; this is consistent with depletion of metal ions by reactions in the acidic environment of the gas plume and vent. Measurements of the size, shape and composition of fine silicate particles may potentially offer insights into preemission, synemission, and postemission processes. The mass flux of fine silicate particles from Mt. Etna released during noneruptive volcanic degassing in 2004 and 2005 was estimated to be ∼7000 kg d−1. Analysis of particles in the range 0.1 < d/μm < 100 by ion chromatography shows that there are persistent differences in the size distributions of sulfate aerosols between the two main summit plumes. Analysis of particles in the range 0.01 μm < d < 0.1 μm by scanning transmission electron microscopy (STEM) shows that there are significant levels of nanoparticles in the Mt. Etna plumes although their compositions remain uncertain.

The Cubatão industrial complex of southeast Brazil is sited on a coastal strip bounded on the continental side by a mountainous scarp covered with tropical forest. Four cities have developed around the complex. The metropolitan region of São Paulo is located on a plateau above the scarp. The combination of the region’s topography, the industrial installations, and an intensely trafficked road network causes widespread atmospheric pollution. In November 2004, measurements were made of the 16 polycyclic aromatic hydrocarbons designated as priority pollutants by the US Environmental Protection Agency, as well as of aerosol mass and ionic composition. Use of characteristic concentration ratios for emission sources show that tailpipe emissions from diesel vehicles was the main source of the compounds. This means that a shift from gasoline to ethanol as fuel in spark ignition engines will have only minor influence on atmospheric polycyclic aromatic hydrocarbon concentrations, despite very low emissions during ethanol combustion. On the other hand, reduction in emissions associated with increasing use of biodiesel in compression ignition engine fuel mixtures could significantly reduce atmospheric concentrations.

Improving the constraints on the atmospheric fate and depletion rates of acidic compounds persistently emitted by non-erupting (quiescent) volcanoes is important for quantitatively predicting the environmental impact of volcanic gas plumes. Here, we present new experimental data coupled with modelling studies to investigate the chemical processing of acidic volcanogenic species during tropospheric dispersion. Diffusive tube samplers were deployed at Mount Etna, a very active open-conduit basaltic volcano in eastern Sicily, and Vulcano Island, a closed-conduit quiescent volcano in the Aeolian Islands (northern Sicily). Sulphur dioxide (SO2), hydrogen sulphide (H2S), hydrogen chloride (HC1) and hydrogen fluoride (HF) concentrations in the volcanic plumes (typically several minutes to a few hours old) were repeatedly determined at distances from the summit vents ranging from 0.1 to similar to 10 km, and under different environmental conditions. At both volcanoes, acidic gas concentrations were found to decrease exponentially with distance from the summit vents (e. g., SO2 decreases from similar to 10 000 mu g/m(3)at 0.1 km from Etna's vents down to similar to 7 mu g/m(3) at similar to 10 km distance), reflecting the atmospheric dilution of the plume within the acid gas-free background troposphere. Conversely, SO2/HC1, SO2/HF, and SO2/H2S ratios in the plume showed no systematic changes with plume aging, and fit source compositions within analytical error. Assuming that SO2 losses by reaction are small during short-range atmospheric transport within quiescent (ash-free) volcanic plumes, our observations suggest that, for these short transport distances, atmospheric reactions for H2S and halogens are also negligible. The one-dimensional model MISTRA was used to simulate quantitatively the evolution of halogen and sulphur compounds in the plume of Mt. Etna. Model predictions support the hypothesis of minor HC1 chemical processing during plume transport, at least in cloud-free conditions. Larger variations in the modelled SO2/HC1 ratios were predicted under cloudy conditions, due to heterogeneous chlorine cycling in the aerosol phase. The modelled evolution of the SO2/ H2S ratios is found to be substantially dependent on whether or not the interactions of H2S with halogens are included in the model. In the former case, H2S is assumed to be oxidized in the atmosphere mainly by OH, which results in minor chemical loss for H2S during plume aging and produces a fair match between modelled and measured SO2/ H2S ratios. In the latter case, fast oxidation of H2S by Cl leads to H2S chemical lifetimes in the early plume of a few seconds, and thus SO2 to H2S ratios that increase sharply during plume transport. This disagreement between modelled and observed plume compositions suggests that more in-detail kinetic investigations are required for a proper evaluation of H2S chemical processing in volcanic plumes.

The abundance and the behavior of metals (Al, Ti, Mn, Fe, Co, Ni, Cu, Zn, Se, Ag, Cd, Sn, Ba, Pt, Hg, and Pb) and ions (Na+ K+ Mg2+ Ca2+, NH4+, Cl-, NO3-, SO4(2-), PO4(3-), and oxalate) in size-fractionated atmospheric particulate matter (PM) were studied in the U. K. and Ireland at four observation sites simulating extreme degrees of vehicular-traffic influence in the environment. Trace metals in urban PM showed distinct types of size-fractionated behavior depending on the particle sources from which they originate. In coarse PM (1.5 < Dp < 3.0 microm) the concentrations of copper, barium, and iron correlated closely across over 2 orders of magnitude in urban air, which is seen as evidence that major portions of transition metals (Cu, Ba, Fe, and Mn) are released through abrasive vehicular emissions, particularly the wear of brake linings. Further results are strongly indicative of a decoupling of coarse iron and calcium, the former arising predominantly from vehicles, the latter from soil resuspension. In fine PM (Dp < 0.5 microm), several combustion and secondary sources of particulates were identified, but these were much less unique in terms of elemental fingerprints. An analysis of the water solubility of trace metals yielded that solubility varies considerably with element and, to a lesser extent, with particle size. Notable differences were found to the elemental water solubilities determined in previous work, partially explained by differences in extraction procedures.

The number concentrations and size distributions of aerosol particles >0.3 μm diameter were measured at the summit of Mount Etna and up to 10 km downwind from the degassing vents during July and August 2004. Aerosol number concentrations reached in excess of 9 × 106 L−1 at summit vents, compared to 4–8 × 104 L−1 in background air. Number concentrations of intermediate size particles were higher in emissions from the Northeast crater compared to other summit crater vents, and chemical composition measurements showed that Northeast crater aerosols contained a higher mineral cation content compared to those from Voragine or Bocca Nuova, attributed to Strombolian or gas puffing activity within the vent. Downwind from the summit the airborne plume was located using zenith sky ultraviolet spectroscopy. Simultaneous measurements indicated a coincidence of elevated ground level aerosol concentrations with overhead SO2, demonstrating rapid downward mixing of the plume onto the lower flanks of the volcano under certain meteorological conditions. At downwind sites the ground level particle number concentrations were elevated in all size fractions, notably in the 2.0–7.5 μm size range. These findings are relevant for assessing human health hazard and suggest that aerosol size distribution measurements may aid volcanic risk management.

An intensive two month measurement campaign has been performed during a two year study of major component composition of urban PM10 and PM2.5 in Ireland (J. Yin, A. G. Allen, R. M. Harrison, S. G. Jennings, E. Wright, M. Fitzpatrick, T. Healy, E. Barry, D. Ceburnis and D. McCusker, Atmos. Res., 2005, 78(3-4), 149-165). Measurements included size-segregated mass, soluble ions, elemental carbon (EC) distributions, fine and coarse fraction organic carbon (OC) and major gases along with standard meteorological measurements. The study revealed that urban emissions in Ireland had mainly a local character and therefore were confined within a limited area of 20-30 km radius, without significantly affecting regional air quality. Gaseous measurements have shown that urban emissions in Ireland had clear, but fairly limited influence on the regional air quality due to favorable mixing conditions at higher wind speeds, in particular from the western sector. Size-segregated mass and chemical measurements revealed a clear demarcation size between accumulation and coarse modes at about 0.8 microm which was constant at all sites. Carbonaceous compounds at the urban site accounted for up to 90% of the particle mass in a size range of 0.066-0.61 microm. Nss SO4(2-) concentrations in PM2.5 were only slightly higher at the urban site compared to the rural or coastal sites, while NO3- and NH4+ concentrations were similar at the urban and coastal sites, but were a factor of 2 to 3 higher than at the rural site. OC was highly variable between the sites and revealed clear seasonal differences. Natural or biogenic OC component accounted for <10% in winter and up to 30% in summer of the PM2.5 OC at urban sites. A contribution of biogenic OC component to PM2.5 OC mass at rural site was dominant.

The Central American volcanic arc supplies a significant proportion of the persistent annual global sulphur dioxide emissions from volcanoes. In November/December 2003, we completed a survey of the arc section from Mombacho to San Cristóbal in Nicaragua recording individual mean fluxes of 800, 530 and 220 Mg day−1 in the plumes from San Cristóbal, Telica and Masaya, respectively. An assessment of fluxes published since 1997 along the entire Central America arc yields a mean total arc flux of SO2 of 4360 Mg day−1 or 8–16% of the annual estimated global volcanic SO2 flux to the troposphere. New field data shows that Masaya volcano continues to show stable HCl/SO2 and HF/SO2 ratios, suggesting a sustained flux of these components of ∼220 and 30 Mg day−1, respectively (1997 to 2004). Masaya's plume composition also appears to have been stable, between 2001 and 2003, with respect to all the particulate species measured, with significant fluxes of SO42− (4 Mg day−1), Na+ (0.9–1.3 Mg day−1) and K+ (0.7 Mg day−1). Extrapolating the Masaya plume species ratios to the entire Central American arc gives mean HCl and HF fluxes of 1300 and 170 Mg day−1 and a particulate sulphate flux of 40 Mg day−1 for 1997 to 2004, although without further understanding of the degassing processes and sources at depth of these different volatiles, these arc-scale estimates should be treated with caution. Combining our arc scale mean SO2 flux with published measurements of volcanic gas compositions with respect to CO2 and H2O allows us to estimate mean CO2 fluxes of 4400–9600 Mg day−1 and H2O fluxes of 70,000–78,000 Mg day−1 for the arc. Preliminary comparisons of these estimates of outgassing rates with published volatile input fluxes into the Central American subduction zone, suggest that Cl is more efficiently recycled through the subduction zone than CO2. The results for H2O are inconclusive.