Observations of nighttime new particle formation in the troposphere

We present atmospheric observations which indicate efficient new particle formation during the nighttime in the troposphere under low condensation sinks, in contrast to the current prevailing assumption that aerosol nucleation takes place only during the daytime and typically from sulfinic acid. High concentrations of ultrafine particles with diameters from 4 to 9 nm (ℓ1000 cm^-3) were measured from the three days of nighttime observations in the upper troposphere during the NSF/NCAR GV Progressive Science Missions. Long-term ground-based observations of charged and neutral clusters and aerosols made in Tumbarumba, Australia, also showed surprisingly high frequency of nighttime new particle formation (30%) with low condensation sinks. Nighttime nucleation can be significant for global aerosol load and cloud condensation nuclei productions and thus needs to be included in global climate models. Future studies are required to understand the nighttime nucleation mechanisms.