Anatomy of the winter 2017 air quality emergency in Delhi

The Indian capital Delhi experienced an environmental emergency in early November 2017 when levels of toxic PM_2.5 particles surpassed WHO guidelines by 25 times (11 times by Indian Standards) for a prolonged period of a week (peak 24 h average ~650 μg/m³). We hereby demonstrate the role that monsoon dynamics played in linking and mixing dust emitted from a large natural dust storm, 3000 km away in the Middle East, with smoke from agriculture fires in northwest India. This dust and smoke rich air was then transported to Delhi where, under stagnant conditions, it mixed with local emissions resulting in very high pollution levels. The heavy aerosol-laden air altered the land-skin surface air temperature difference resulting in increased surface wind speeds, favouring faster dispersion and an unusual sharp decline in PM_2.5 (PM_2.5-110 μg/m³). Understanding the multi-scale nature of such events is important in improving our abilities to forecast these events and in developing effective air quality management strategies for the mega cities.

Biofuels that cause land-use change may have much larger non-GHG air quality emissions than fossil fuels

Although biofuels present an opportunity for renewable energy production, significant land-use change resulting from biofuels may contribute to negative environmental, economic, and social impacts. Here we examined non-GHG air pollution impacts from both indirect and direct land-use change caused by the anticipated expansion of Brazilian biofuels production. We synthesized information on fuel loading, combustion completeness, and emission factors, and developed a spatially explicit approach with uncertainty and sensitivity analyses to estimate air pollution emissions. The land-use change emissions, ranging from 6.7 to 26.4 Tg PM(2.5), were dominated by deforestation burning practices associated with indirect land-use change. We also found Brazilian sugar cane ethanol and soybean biodiesel including direct and indirect land-use change effects have much larger life-cycle emissions than conventional fossil fuels for six regulated air pollutants. The emissions magnitude and uncertainty decrease with longer life-cycle integration periods. Results are conditional to the single LUC scenario employed here. After LUC uncertainty, the largest source of uncertainty in LUC emissions stems from the combustion completeness during deforestation. While current biofuels cropland burning policies in Brazil seek to reduce life-cycle emissions, these policies do not address the large emissions caused by indirect land-use change.

The effect of the limited availability of H2O2 in the competitive deposition of sulfur and oxidized nitrogen

To understand the influence of the reduction of SO2 emissions from a single source in the S and N deposition around its local environment, the application of the Sulphur Transport Eulerian Model 2 (STEM-II) was introduced in this paper. Observed local deposition patterns were analysed and explained in terms of the main processes involved in the pollutants deposition. It was necessary to take into account the limited availability of H2O2 because of its influence on both S(IV) and oxidized nitrogen deposition. In order to estimate the quantitative relationship between the SO2 emissions reduction and the observed S and N deposition patterns, these processes were simulated for different meteorological conditions. Simulation results were in agreement with both observed deposition patterns and limited availability of H2O2, specially if significant changes in the S deposition patterns were considered. Both observed and estimated S deposition patterns changed their top value location from the Southwest (1990) to the Northwest (1997) of the domain, because of the reduction of dry deposition. The global reduction of total S depositions, estimated and observed, were in good agreement too. Model simulations could explain the higher S dry deposition reduction, considering the emissions reduction strategy applied.

Acid rain and acidification in China: the importance of base cation deposition

Acid deposition has been recognized as a serious environmental problem in China. Most acid deposition studies have focused on sulfur deposition and the pH of precipitation. However, as high concentration of alkaline dust is an important feature of the atmosphere in large parts of China, base cation deposition must be taken into account when discussing possible effects on soils and vegetation from acid deposition. We estimate the deposition of sulfur as well as calcium, i.e. the dominating anion and cation, on a regional scale in China using data both from measurements and modeling. The ratio of sulfur/calcium in deposition is then used as an indicator for identifying areas where deposition acidity exceeds alkalinity, and where soils may be at risk to acidification. The dynamic soil acidification model MAGIC is applied with data from two sites receiving high deposition loads in southwest China. The model predictions indicate that considerable soil acidification has been going on for the last decades due to acid deposition inputs. Effects on the spatial distribution of acidic deposition in China, using different future deposition scenarios, are illustrated. As the size of the anthropogenic fraction of the base cation deposition is unknown, different possible future trends in calcium deposition were used. Soil response, according to the model, using different combinations of sulfur and calcium deposition scenarios is shown. Applying the most strict measures to reduce sulfur emission will almost eliminate the acid deposition problem; however, such a scenario is not economically feasible in the short term. A strict, but possibly realistic, future scenario for sulfur may be enough to keep the situation at the present level, assuming only moderate reductions in calcium deposition. With large decreases in base cation deposition, increased soil acidification can be expected even with considerable sulfur emission reductions.

General model for dissolution rates of n-component, nondisintegrating spheres

The dissolution rates of compressed spheres consisting of two and three components were measured. A general model for dissolution rates of n-component, nondisintegrating spheres is discussed. Experimental cases are presented to support the model for two- and three-component spheres, two-component interacting spheres, and three-component spheres containing two components that complex.