Nature and sources of ionic species in rainwater during monsoon periods in and around sixteenth-seventeenth century CE monuments in Yamuna River basin, India

The nature and sources of ionic species were studied in the monsoon rainwater collected from two monuments of the sixteenth-seventeenth century CE in the Yamuna River basin from 2016 to 2018. The results showed the acidic pH of the rainwater with high dissolved SO₄^-2 and NO₃^-, and soil-derived components (Ca⁺², Mg⁺², and K⁺). The anionic (SO₄^-2, NO₃^-, Cl^-, F^-, and HCO₃^-) and cationic (Ca⁺², Mg⁺², K⁺, NH₄⁺, and Na⁺) concentrations showed regional differences in yearly contribution mainly from the fossil fuel combustion, soil dust, and farm residue burning. The rainwater analysis showed low dissolved ions at SCTK (Sheikh Chilli's Tomb, Kurukshetra) compared to KBMP (Kabuli Bagh Mosque, Panipat). The mean concentration of SO₄^-2 was 1.5 times higher than the NO₃^- apportioning the sulfate as a dominant acidifying constituent in rainwater. Pearson's correlation and principal component analysis (PCA) showed terrestrial and marine origins of dissolved ions in the rainwater. The Na-normalized molar ratios and the analysis of sea salt and non-sea salt fractions indicate the dominance of non-marine contributions in the precipitation. Based on neutralization factors, cations showed neutralization of rainwater acidity as follows: NF_Ca⁺² > NF_Mg⁺² > NF_NH4⁺ > NF_K⁺. The potential index showed the dominance of the neutralization potential (NP) on acidic potential (AP) at both locations.

Sources and levels of particulate matter in North African and Sub-Saharan cities: a literature review

In order to assess the significance of PM in ambient air, it is necessary to evaluate their physical and chemical characteristics as well as identify their major emission sources. On a global scale, particulate matter in the atmosphere arises mainly from the combustion process of motorized vehicles, but natural sources are still considered as the major contributors. In Africa, PM emissions differ from those in developed countries; human activities such as biomass burning in households, poor household waste management, and the high number of diesel-powered vehicles are the predominant anthropogenic sources. Natural contributions are also observed. Saharan dust and savanna fires are the most common atmospheric natural sources of particulate matter. The present literature review gives an overview of the status of air quality in African cities and highlights the various sources of particulate matter emissions and local human activities specific to each African region. This could likely serve as a reference to evaluate the current air quality in this region and will be a useful tool in the future to develop pollution mitigation strategies at the source. Recommendations are proposed in the conclusion in order to reduce emissions from their sources, taking into account the low-income African countries.

Modeling secondary organic aerosol formation via multiphase partitioning with molecular data

A new model for atmospheric secondary organic aerosol (SOA) is presented for biogenic compounds. It is based to the extent possible on experimental molecular SOA data, and it is compatible with any existing gas-phase chemical kinetic mechanism. Six SOA precursors or groups of precursors are used to represent biogenic monoterpenes and sesquiterpenes. SOA formation is modeled using five SOA surrogates to represent classes of compounds with different partitioning properties, e.g., hydrophobicity, aqueous solubility, acid dissociation, and saturation vapor pressure. Model simulations are evaluated against smog chamber data for SOA yields and some adjustments are made to uncertain stoichiometric coefficients and saturation vapor pressure parameters to improve model performance. The model is applied undertypical atmospheric conditions to exemplify the effect of relative humidity on SOA formation and the relative contributions of hydrophilic and hydrophobic SOA.

Direct observation of completely processed calcium carbonate dust particles

This study presents, for the first time, field evidence of complete, irreversible processing of solid calcium carbonate (calcite)-containing particles and quantitative formation of liquid calcium nitrate particles apparently as a result of heterogeneous reaction of calcium carbonate-containing mineral dust particles with gaseous nitric acid. Formation of nitrates from individual calcite and sea salt particles was followed as a function of time in aerosol samples collected at Shoresh, Israel. Morphology and compositional changes of individual particles were observed using conventional scanning electron microscopy with energy dispersive analysis of X-rays (SEM/EDX) and computer controlled SEM/EDX. Environmental scanning electron microscopy (ESEM) was utilized to determine and demonstrate the hygroscopic behavior of calcium nitrate particles found in some of the samples. Calcium nitrate particles are exceptionally hygroscopic and deliquesce even at very low relative humidity (RH) of 9-11% which is lower than typical atmospheric environments. Transformation of non-hygroscopic dry mineral dust particles into hygroscopic wet aerosol may have substantial impacts on light scattering properties, the ability to modify clouds and heterogeneous chemistry.