Light Absorption for Volatile Aerosol Particles: A New Measurement Approach
Lead Research Organisation:
University of Bristol
Department Name: Chemistry
Abstract
Aerosols are liquid or solid particles suspended in a gas and are pervasive in our atmosphere. Sources of atmospheric aerosol include anthropogenic emissions from burning of fossil fuels, and natural sources from sea spray, desert dust, and biomass burning sources such as wildfires. These aerosols have significant impacts on our environment, affecting regional air quality as well as global climate through interacting with sunlight and cloud droplets. Indeed, the representation of aerosols in atmospheric models is one of the largest uncertainties in predicting future climate. Globally, the net aerosol cooling effect provided by aerosol particles scattering sunlight back to space partially offsets the warming impact of greenhouse gases. On a regional basis, light absorbing aerosols such as those from combustion can heat the atmosphere, driving changes in atmospheric dynamics and regional meteorology such as the formation of clouds. However, large uncertainties in quantifications of aerosol-light interactions degrade the confidence we have in models of regional meteorology and of future climate. Improvements to our understanding of aerosol-light interactions could lead to more effective risk mitigation strategies in managing climate change impacts.
Aerosol light absorption is particularly uncertain and is represented poorly in climate models. In part, this uncertainty arises from poor observations of aerosol absorption that hamper the development of accurate descriptions of aerosol optical properties and how these depend on factors such as aerosol source, lifetime, and ambient humidity. Thus, very recent years have seen the development of photoacoustic spectroscopy (PAS) techniques that can be deployed from atmospheric research aircraft for in situ sampling of aerosol absorption. Dr Cotterell has collaborated with Met Office researchers in developing bespoke, internationally-leading PAS instruments that are deployed from the FAAM research aircraft, providing the atmospheric science community with extensive observations of aerosol light absorption. However, as with other techniques that directly quantify aerosol absorption, PAS measurements are limited to particles that do not contain any volatile components (such as water); the presence of in-aerosol volatiles introduces significant biases in determined absorption coefficients arising from evaporative effects during spectroscopic interrogation. Indeed, there is very little knowledge of how aerosol absorption varies with water uptake in the elevated humidity environments often encountered, and thus the variation in absorption with humidity is neglected in atmospheric models. Thus, it is of paramount importance that new techniques are developed that enable observations of absorption for volatile-containing particles.
This project develops a new implementation of photoacoustic spectroscopy, referred to as phase shift photoacoustic spectroscopy (PS-PAS), that provides additional phase shift information during measurements on aerosol samples. Through a series of laboratory experiments in combination with modelling of photoacoustic energy transfer processes, we will demonstrate that PS-PAS data enable the correction of measured aerosol absorption coefficients for evaporative effects. In addition to providing robust characterisations of light absorption, the new phase shift data products will allow studies of aerosol particle volatility, a key property needed in climate models to predict the evolving number concentration, size distribution, and chemical composition for atmospheric aerosols. Importantly, these instruments will be readily available for deployment from the FAAM research aircraft, providing the UK with new, world leading observational capability. For the first time, atmospheric scientists will have the critical data sets required for developing new and accurate descriptions of aerosol absorption, as well as volatility, for the next generation of climate models.
Aerosol light absorption is particularly uncertain and is represented poorly in climate models. In part, this uncertainty arises from poor observations of aerosol absorption that hamper the development of accurate descriptions of aerosol optical properties and how these depend on factors such as aerosol source, lifetime, and ambient humidity. Thus, very recent years have seen the development of photoacoustic spectroscopy (PAS) techniques that can be deployed from atmospheric research aircraft for in situ sampling of aerosol absorption. Dr Cotterell has collaborated with Met Office researchers in developing bespoke, internationally-leading PAS instruments that are deployed from the FAAM research aircraft, providing the atmospheric science community with extensive observations of aerosol light absorption. However, as with other techniques that directly quantify aerosol absorption, PAS measurements are limited to particles that do not contain any volatile components (such as water); the presence of in-aerosol volatiles introduces significant biases in determined absorption coefficients arising from evaporative effects during spectroscopic interrogation. Indeed, there is very little knowledge of how aerosol absorption varies with water uptake in the elevated humidity environments often encountered, and thus the variation in absorption with humidity is neglected in atmospheric models. Thus, it is of paramount importance that new techniques are developed that enable observations of absorption for volatile-containing particles.
This project develops a new implementation of photoacoustic spectroscopy, referred to as phase shift photoacoustic spectroscopy (PS-PAS), that provides additional phase shift information during measurements on aerosol samples. Through a series of laboratory experiments in combination with modelling of photoacoustic energy transfer processes, we will demonstrate that PS-PAS data enable the correction of measured aerosol absorption coefficients for evaporative effects. In addition to providing robust characterisations of light absorption, the new phase shift data products will allow studies of aerosol particle volatility, a key property needed in climate models to predict the evolving number concentration, size distribution, and chemical composition for atmospheric aerosols. Importantly, these instruments will be readily available for deployment from the FAAM research aircraft, providing the UK with new, world leading observational capability. For the first time, atmospheric scientists will have the critical data sets required for developing new and accurate descriptions of aerosol absorption, as well as volatility, for the next generation of climate models.
