Atmospheric water-soluble organic gases such as pyruvic acid are produced in large quantities by 13 photochemical oxidation of biogenic and anthropogenic emissions and undergo water-mediated 14 reactions in aerosols and hydrometeors. These reactions can contribute to aerosol mass by forming 15 less volatile compounds. While progress is being made in understanding the relevant aqueous 16 chemistry, little is known about the chemistry that takes place during droplet evaporation. Here we 17 examine the evaporation of aqueous pyruvic acid droplets using both the Vibrating Orifice Aerosol 18 Generator (VOAG) and an electrodynamic balance (EDB). In some cases pyruvic acid was first 19 oxidized by OH radicals. The evaporation behavior of oxidized mixtures was consistent with 20 expectations based on known volatilities of reaction products. However, independent VOAG and 21 EDB evaporation experiments conducted without oxidation also resulted in stable residual 22 particles; the estimated volume yield was 10-30% of the initial pyruvic acid. Yields varied with 23 temperature and pyruvic acid concentration across cloud, fog, and aerosol-relevant concentrations. 24The formation of low volatility products, likely cyclic dimers, suggests that pyruvic acid accretion 25 reactions occurring during droplet evaporation could contribute to the gas-to-particle conversion 26 of carbonyls in the atmosphere. 27 mass. [4][5][6] However, the contribution of aqueous reactions to SOA mass remains uncertain due in 35 part to a limited understanding of precursors and limited laboratory results to parameterize 36 models. 1,[7][8][9][10][11] Quantifying the impacts of aqueous and multiphase chemistry on aerosol mass 37 remains challenging, and a more detailed understanding of product volatility is needed.A significant fraction of low molecular weight acids, aldehydes and carbonyls dissolve into 39 cloud or fog droplets. In the absence of additional reactions, these WSOGs largely evaporate 40 during water evaporation; the trace amounts that remain in the aerosol phase are determined by 41 their partial pressure in the gas phase and activity in the aerosol matrix. However, multiphase 42 reactions can generate low-volatility products that are retained in the equilibrated aerosol. Several 43 important criteria determine whether aqueous processing can appreciably increase SOA mass: (1) 44 the precursor must be abundant, (2) it must have a high vapor pressure before aqueous reactions, 45(3) it must have a high Henry's law coefficient and thus strongly partition into water, and (4) it 46 must react in the aqueous phase to form less volatile products. 47