Towards long term observation of individual aerosol particle charging with optical tweezers

Aerosol particles, including dust, pollen and viruses, surround us in our everyday lives. These particles are often electrostatically charged. Charge can accumulate on aerosol particles due to various mechanisms, including interactions with other particles and scavenging of ions. The charge of microscopic particles and aerosols can influence aggregation and how long particles remain airborne: understanding the microscopic nature of aerosol charging can give important insights into the behaviour of larger systems such as dust transport across oceans and air filtration. In order to study how the charge evolves on individual micro-meter sized aerosol particles, we need a non-contact technique capable of holding both charged and uncharged particles. Optical tweezers are one such tool. Our group has been using optical tweezers to study charging of aerosol particles: preliminary results suggest that the rate at which particles charge depends on numerous factors, most importantly, the humidity of the surrounding air. Our hypothesis is that this occurs due to preferential adsorption/desorption of OH- or H+ ions. When we artificially increase the number of ions surrounding our particle, we observe rapid discharging. Currently we have only studied charging behavior over relative short time frames (several hours) due to limitations in system stability. We are working towards extending the capabilities of our system to study charging over longer time frames.