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It concerns the open access paper published as a Review paper by Baker et al., Sci. Adv. 2021; 7 : eabd8800 7 July 2021, with the following abstract "Anthropogenic emissions to the atmosphere have increased the flux of nutrients, especially nitrogen, to the ocean, but they have also altered the acidity of aerosol, cloud water, and precipitation over much of the marine atmosphere. For nitrogen, acidity-driven changes in chemical speciation result in altered partitioning between the gas and particulate phases that subsequently affect long-range transport. Other important nutrients, notably iron and phosphorus, are affected, because their soluble fractions increase upon exposure to acidic environments during atmospheric transport. These changes affect the magnitude, distribution, and deposition mode of individual nutrients supplied to the ocean, the extent to which nutrient deposition interacts with the sea surface microlayer during its passage into bulk seawater, and the relative abundances of soluble nutrients in atmospheric deposition. Atmospheric acidity change therefore affects ecosystem composition, in addition to overall marine productivity, and these effects will continue to evolve with changing anthropogenic emissions in the future. "

This study explores the drivers of aerosol pH and their impact on the inorganic fraction and mass of aerosol in the S.E. Canadian urban environments of Hamilton and Toronto, Ontario. We find that inter-seasonal pH variability is mostly driven by temperature changes, which cause variations of up to one pH unit. Wintertime acidity is reduced, compared to summertime values. Because of this, the response of aerosol to precursors fundamentally changes between seasons, with a strong sensitivity of aerosol mass to levels of HNO3 in the wintertime. Liquid water content (LWC) fundamentally influences the aerosol sensitivity to NH3 and HNO3 levels. In the summertime, organic aerosol is mostly responsible for the LWC at Toronto, and ammonium sulfate for Hamilton; in the winter, LWC was mostly associated with ammonium nitrate at both sites. The combination of pH and LWC in the two sites also affects N dry deposition flux; NO3− fluxes were comparable between the two sites, but NH3 deposition flux at Toronto is almost twice what was seen in Hamilton; from November to March N deposition flux slows down leading to an accumulation of N as NO3− in the particle phase and an increase in PM2.5 levels. Given the higher aerosol pH in Toronto, aerosol masses at this site are more sensitive to the emission of HNO3 precursors compared to Hamilton. For both sites, NOx emissions should be better regulated to improve air quality during winter; this is specifically important for the Toronto site as it is thermodynamically more sensitive to the emissions of HNO3 precursors.

Inflammatory allergic and nonallergic respiratory disorders are spreading worldwide and often coexist. The root cause is not clear. This review demonstrates that, from a biochemical point of view, it is ascribable to protons (H+) released into cells by exogenous and endogenous acids. The hypothesis of acids as the common cause stems from two considerations: a) it has long been known that exogenous acids present in air pollutants can induce the irritation of epithelial surfaces, particularly the airways, inflammation, and bronchospasm; b) according to recent articles, endogenous acids, generated in cells by phospholipases, play a key role in the biochemical mechanisms of initiation and progression of allergic-type reactions. Therefore, the intracellular acidification and consequent Ca2+ increase, induced by protons generated by either acid pollutants or endogenous phospholipases, may constitute the basic mechanism of the multimorbidity of these disorders, and environmental acidity may contribute to their spread.

Having observed great variations in the strong primary acidity (SPA) content of the ash of fossil fuels with similar sulphur contents, we studied the chemical causes of the formation of SPA in ashes. The main factors behind these variations were found to be: (a) combustion conditions and the extent to which they favour or do not favour the formation of SO 3 (excess of oxygen, presence of suitable catalysts, etc.); (b) the amount of basic oxides present in the mineral fraction of the fuel in relation to the SO 3 produced; and (c) the basic strength of these oxides. The variable but, nevertheless, high SPA contents common only to oil ashes can be explained in the light of the modest values for factors (b) and (c) and the conditions favourable to factor (a) in this fuel. Remedies involve the in-flame addition of highly basic oxides in order to artificially increase factors (b) and (c).

The fly ashes produced by the burning of heavy oil have been identified in this study as carriers of strong primary acidity in the atmosphere in the form of sulphuric acidity and hydrolyzable metal ions. This is an acidity which is strong from the moment of its emission (strong primary acidity, SPA) and different from common sources of weak acidity (SO2 NO) which give rise to strong acidity only after some time in the atmosphere. The oil ash SPA is transmitted to water on impact resulting in highly acid pH values and high total acidity as well as significant concentrations of heavy metals. Here we present and discuss our results.