NEW PARTICLE FORMATION IS THE SOURCE OF AROUND HALF OF ALL CLOUD CONDENSATION NUCLEI IN THE TROPOSPHERE. THE SENSITIVITY OF AIR QUALITY WEATHER AND CLIMATE TO NEW PARTICLE FORMATION DEPENDS ON THE NUMBER OF PARTICLES FORMED THE NUMBER THAT SURVIVE AND REACH THE SIZE NEEDED TO FORM CLOUD DROPLETS AND ON METEOROLOGICAL CONDITIONS THAT DETERMINE THE AEROSOL-CLOUD INTERACTIONS. AEROSOL-CLOUD INTERACTIONS CAUSE THE LARGEST UNCERTAINTY ON RADIATIVE FORCING OF EARTH S CLIMATE IDENTIFIED BY THE IPCC. CONSTRAINING CLOUD DROPLET CONCENTRATIONS AND HOW THEY HAVE CHANGED WITH TIME VIA MORE REALISTIC DESCRIPTIONS OF THE AEROSOL FORMATION AND GROWTH PROCESS IS AN OBVIOUS STRATEGY TO REDUCE THIS UNCERTAINTY. THIS PROPOSAL WILL UPGRADE THE REPRESENTATIONS OF AEROSOL FORMATION AND GROWTH USED IN CLIMATE NUMERICAL WEATHER PREDICTION AND AIR QUALITY MODELS.