Exploring the use of ground-based remote sensing to identify new particle formation events: A case study in the Beijing area.

New Particle Formation (NPF) is an important process of secondary aerosol production in the atmosphere, which
has significant impacts on the Earth's radiation balance, air quality, and climate change. In this study, we develop
a method to identify NPF events based on ground-based remote sensing. We propose a proxy to characterize NPF
events utilizing ground-based remote sensing of gaseous precursors and aerosol optical depth (AOD). This proxy
is applied to identify the NPF events in Beijing in the winter of 2022 and tested by comparison with in-situ
observations of aerosol particle number size distributions (PNSD) from SMPS. The comparison shows that the
NPF events for regional nucleation can be identified effectively when the threshold for sulfur dioxide and organic
gases (i.e. formaldehyde) are determined as 0.44 × 10 4 and 1.07 × 10 4. Based on these thresholds, the NPF
events can be identified at a high percentage (84 %) compared with in-situ observations. The relationship be-
tween identification of NPF events and meteorological conditions shows that NPF events in Beijing winter
occurred more frequently under weather conditions with north-west wind direction, high wind speed and low
relative humidity.