We study the physical and chemical properties of aerosols using single particle mass spectrometry and optical trapping approaches. Aerosols are relevant to a wide range of applications, from climate to health to materials science, so our work is by nature highly interdisciplinary. We develop our own instruments to tackle important questions about aerosol processes and properties. Current research interests include resolving the factors that govern photoinitiated chemistry in aerosols, quantifying the surface composition of picolitre volume droplets, and elucidating the growth mechanisms of engineered nanoparticles.