Non-linear photochemical pathways in laser induced atmospheric aerosol formation

TL;DR

This study investigates how femtosecond laser pulses induce aerosol formation in the atmosphere, revealing the chemical composition, size distribution, and the effects of water droplets on particle growth.

Contribution

It provides new insights into the non-linear photochemical pathways involved in laser-induced atmospheric aerosol formation, highlighting the roles of nitric acid and organics.

Findings

Nitric acid condenses as ammonium nitrate in aerosols.

Oxidized organics significantly contribute to particle growth.

Water droplets enhance organic condensation under laser illumination.

Abstract

We measured the chemical composition and the size distribution of aerosols generated by femtosecond-Terawatt laser pulses in the atmosphere using an aerosol mass spectrometer (AMS). We show that nitric acid condenses in the form of ammonium nitrate, and that oxidized volatile organics also contribute to particle growth. These two components account for two thirds and one third, respectively, of the dry laser-condensed mass. They appear in two different modes centred at 380 nm and 150 nm. The number concentration of particles between 25 and 300 nm increases by a factor of 15. Pre-existing water droplets strongly increase the oxidative properties of the laser-activated atmosphere, substantially enhancing the condensation of organics under laser illumination.