  Sea salt aerosols composed mainly of micrometer-sized sodium chloride
particles not only pose a potential threat to human health and traffic safety,
but also directly affect climate prediction. The long-range and high-precision
sensing of sea salt aerosols remains a challenge for existing composition
analysis methods. As the development of ultrashort laser technology,
femtosecond laser filamentation provides a new opportunity for molecular remote
sensing in complex environments. However, the accuracy at long-distance of this
method is still hard to meet the demand (<10 ng/m3) for the remote aerosol
monitoring. To solve this problem, we built a remote detection system for sea
salt aerosol fluorescence spectroscopy and obtained a very high system
sensitivity by introducing a terawatt-class high-performance femtosecond laser
and optimizing the filament and aerosol interaction length. The system achieves
a Na+ detection limit of 0.015 ng/m3 at a detection distance of 30 m, and 0.006
ng/m3 when supplemented with a deep processing learning algorithm.
