Anthropogenic pollution elevates the peak height of new particle formation from planetary boundary layer to lower free troposphere

New particle formation (NPF) and subsequent growth are primary sources of atmospheric aerosol particles and cloud condensation nuclei. Previous studies have been conducted in relatively clean environments; investigation of NPF events over highly polluted megacities is still lacking. Here we show, based on a recent yearlong aircraft campaign conducted over Beijing, China, from April 2011 to June 2012, that NPF occurrence peaks in the lower free troposphere (LT), instead of planetary boundary layer (PBL), as most previous studies have found and that the distance of NPF peak to PBL top increases with increasing aerosol loading. Further analysis reveals that increased aerosols suppress NPF in PBL, but enhance NPF in LT due to a complex chain of aerosol-radiation-photochemistry interactions that affect both NPF sources and sinks. These findings shed new light on our understanding of NPF occurrence, NPF vertical distribution, and thus their effects on atmospheric photochemistry, clouds, and climate. Plain Language Summary Comparing with planetary boundary layer (PBL) and upper free troposphere (UT), the lower free troposphere (LT) is thought as weak new particle formation (NPF) region, where particles are thus thought to be either uptransported from PBL or downtransported from UT. Whereas, such distribution seems to be changed under highly aerosol-polluted regions. Our observations collected during a yearlong (April 2011 to June 2012) aircraft field campaign over Beijing, China, show that NPF peak region has been elevated from PBL to LT. Further analysis reveals that increased aerosols suppress NPF in PBL but enhance NPF in LT due to a complex chain of aerosol-radiation-photochemistry interactions that affect both NPF sources and sinks. These findings shed new light on our understanding of NPF occurrence, NPF vertical distribution, and thus their effects on atmospheric photochemistry, clouds, and climate.