There's no smoke without fire: A deep time perspective on the effects of fires on air quality, human health and habitability in the Palaeolithic and prehistory

The use and control of fire is arguably one of the most important technological advancements of the Homo genus. Prehistoric populations exploit the combustion properties of fires (light, heat and smoke) for daily tasks such as food preparation, insect repellent, extension of daylight hours and modification of technology. The habitual use of fire can however lead to significant health implications through sustained exposure to smoke which can affect air quality resulting in respiratory complications. While smoke is often an important tool in hunter-gatherer activities such as smoking meats, curing hides, accessing highly prized food items' such as honey and as an insect repellent, to date, little research has been conducted on the actual levels of exposure to harmful toxins contained in smoke that Palaeolithic hunter-gatherers would have been exposed to during their daily lives. In this paper, we present a new methodological protocol for future studies wishing to examine the effects of smoke from open fires on air quality, human health and habitability in the Palaeolithic using environmental monitoring systems. We present the first systematic study of concentration levels of harmful particulate matter (PM2.5) in smoke relative to the use of other combustion properties of fires (light, smoke and radiative heat) from a wide range of fuels used in Palaeolithic fireplaces, recording different types of fires (smoking, glowing and flaming) and activity types (smoking food items, sleeping and cooking). Our empirical findings highlight significant variability in light and heat output, as well as concentrations of harmful particulate matter in smoke (PM2.5). We argue that this variation and the aim to minimise exposure to the harmful elements of smoke, likely influenced the placement of fixed fire features in habitation spaces whether open, semi-open and closed (outdoors, rock shelters, caves, huts and houses) relative to the use of combustion properties. Our results also show how humanenvironment interactions around fire, fuel and habitability (air quality) may have changed over time in some living structures from the Palaeolithic through to later time periods (Neolithic and Iron Age).