Alkaline air: changing perspectives on nitrogen and air pollution in an ammonia-rich world

Abstract

Ammonia and ammonium have received less attention than other forms of air pollution, with limited progress in controlling emissions at UK, European and global scales. By contrast, these compounds have been of significant past interest to science and society, the recollection of which can inform future strategies. Sal ammoniac ( nūshādir , nao sha ) is found to have been extremely valuable in long-distance trade ( ca AD 600–1150) from Egypt and China, where 6–8 kg N could purchase a human life, while air pollution associated with nūshādir collection was attributed to this nitrogen form. Ammonia was one of the keys to alchemy—seen as an early experimental mesocosm to understand the world—and later became of interest as ‘alkaline air’ within the eighteenth century development of pneumatic chemistry. The same economic, chemical and environmental properties are found to make ammonia and ammonium of huge relevance today. Successful control of acidifying SO 2 and NO x emissions leaves atmospheric NH 3 in excess in many areas, contributing to particulate matter (PM 2.5 ) formation, while leading to a new significance of alkaline air, with adverse impacts on natural ecosystems. Investigations of epiphytic lichens and bog ecosystems show how the alkalinity effect of NH 3 may explain its having three to five times the adverse effect of ammonium and nitrate, respectively. It is concluded that future air pollution policy should no longer neglect ammonia. Progress is likely to be mobilized by emphasizing the lost economic value of global N emissions ($200 billion yr −1 ), as part of developing the circular economy for sustainable nitrogen management. This article is part of a discussion meeting issue ‘Air quality, past present and future’.

A chronology of global air quality

“…It is notable that the reference to the brain matches an effect of ammonium-containing air pollution from naturally burning coal caves along the Silk Road in Central Asia as later recorded by the Arab geographer Al-Mas'ūdī [16]. A book by Shen Kuo (1031-1095) written during the Song Dynasty (AD 961-1279) provides further evidence of concern in China about air pollution from coal burning [17].…”

“…Emissions from combustion were the main contributors to poor air quality, but they were not the only pollutants. It is important to mention emissions of NH 3 from the large urban population of horses for transport, which would have added to NH 3 released by coal combustion [16]. The quantity of horse dung on urban roads was recognized as a growing problem in the late nineteenth century, for example 100 000 horses in New York producing 1000 tonnes of manure daily (the 'great manure crisis' in New York and London; [28]), with a major problem projected into future decades.…”

“…Whether these benefits lead to longer-term reductions in emissions is much less clear as transport and industrial emissions grow following the widespread population lockdown. It seems likely that an effect of COVID-19 will be to reduce net acidity and increase the gaseous alkaline fraction [16] as transport and combustion emission are reduced, but with little anticipated reduction in NH 3 emissions from agriculture. While this may be associated with health benefits, additional adverse effects of 'alkaline air' on ecosystems will also need to be considered.…”

Wanted: virtual or live! How lichens are becoming part of mass internet culture

“…Although able to grow in harsh environmental conditions, the impact of anthropogenic activities on lichens is considerable and their use as sensitive bioindicators of environmental change is widely established (e.g. Abas 2021;Nimis et al 2002;Sutton et al 2020). When extensive or rapid environmental changes occur, some species are unable to adapt (Munzi et al 2020), yet lichens respond to climate changes and environmental stress with shifts in community composition (Nimis et al 2002;van Herk 2001), physiological impairment (Paoli et al 2015;Yemets et al 2015) and finally, with their disappearance (Isocrono et al 2007;Munzi et al 2007).…”

Global Air Quality, past present and future: an introduction

“…The role of nitrogen compounds on air quality has grown since the mid-twentieth century, especially with the declining role of sulfur dioxide emissions. The papers by Sutton et al [11] and Liu et al [12] both focus on the role of nitrogen compounds. Sutton et al address the issue of ammonia and specifically its role in regulating the acidity of the atmosphere.…”