Climate change : how guilty are aerosol particles ?

Aerosol particles may be tiny enough to escape gravity and float up for days in the atmosphere, but their impact on the climate is anything but. These suspensions of solid or liquid particles, scaling from nanometers to tens of microns, can arise from both natural (sand dust, volcanic emissions, sea salt, forest fires) and human sources (anthropogenic fuel combustion and biomass burning). These particles have two opposite but complementary effects on the climate : they cool down the earth by blocking and sending some of the Sun's rays back to space (the parasol effect), and warm it up by contributing to trapping infrared rays emitted by the surface in the atmosphere (the famous greenhouse effect). But the increase in greenhouse gas emissions resulting from human activity is distorting the balance, making particles active contributors to climate change. Moreover the aerosols are chemical constituents that degrade the air quality, thereby constituting a threat to human health.

For more than a decade now, scientist have been investigating the role these tiny particles play in warming the climate and on human health, but many grey areas remain. Among them are the exact roles of three types of aerosols : black carbon (BC), brown carbon (BrC) and soil dust particles. Dr. Paolo Tuccella's project aims to enrich and enhance current air quality and climate-chemistry models by investigating the space-time distribution of these particles and their effects on the climate system. The ultimate objective is to contribute to the development and implementation of effective sustainable risk mitigation policies by providing a better understanding of the environmental risks associated with BC, BrC and soil dust particles.

Shedding light on grey areas

"The effects of aerosols on the climate are still largely unknown because their treatment in current models is insufficient", Dr. Paolo Tuccella points out. "We need to further investigate their impact on environmental change and that means including aerosols which have been ignored or insufficiently studied in the past and their impact on various environmental components"."Unlike black carbon, which has been known for some time to absorb sunlight and warm the atmosphere, brown carbon, its organic cousin, is just beginning to be taken into account as a possible contributor to climate change ", the researcher in atmospheric physics explains. "Including this species in current models is crucial if we want to obtain more realistic estimates". In addition to investigating the role of brown carbon on environmental change, Dr. Paolo Tuccella also intends to shed light on two other major grey areas of aerosol research. Specifically, the project aims to study the effect of ageing on the ability of aerosols to scatter and absorb light, as well as the impact of aerosol particles deposition on the capacity of ice to reflect light. "The latter phenomenon likely contributes to an enhancement of the melting of Arctic sea ice, Arctic and Alpine glaciers and snow pack", the researcher specifies. Taking these three innovative aspects into account, Dr. Paolo Tuccella aims to obtain better estimates of the budget of BC, BrC and soil dust and to refine our understanding of the direct and indirect radiative effect of these particles at global and European scales with a focus on the Mediterranean basin.

The Earth's radiation field relies on a fragile balance. Over the course of history, naturally-processed aerosols have proven their ability to punctually offset this balance and affect the Earth's climate. A recent example is the eruption of Mount Pinatubo in 1991, whose production of sulphate aerosols pushed down global average temperatures for as long as two to three years. But the emission of particles resulting from human activity is now threatening to durably throw the Earth's climate off balance, with far-reaching, long-lasting and, in many cases, devastating effects. To avoid an irreversible build-up of nocive and climate forcing particles, we need to act urgently and efficiently. In this sense, initiatives such as Dr. Paolo Tuccella's project are absolutely crucial to the implementation of informed and effective mitigation policies.