The production of carbonyls during use of an electronic nicotine delivery system (ENDS) is of high concern, and several carbonyls appear in FDA’s list of suggested analytes for ENDS testing. Therefore, close monitoring of the levels and sources of carbonyls is of prime importance. Production of carbonyls is generally associated with the thermal degradation of e-liquid components during the heating and aerosolization process, but carbonyls can also form in the e-liquid. The carbonyls present in the aerosols are hypothesized to come from two sources - the carbonyls formed in the e-liquid and those produced during aerosolization. In this work, we study the formation of carbonyls in e-liquids after exposure to accelerated storage conditions (40 °C at 60% RH) to determine its relative contribution. Standard carbonyl analysis using DNPH complexation followed by LC-MS detection was employed to determine the carbonyl content of the e-liquid and aerosolized e-liquid prior to accelerated storage (T=0) and after 30 days of accelerated storage (T=30). At the T=0 timepoint formaldehyde was found to originate primarily due to the aerosolization process (0.010 ± 0.02 µg/mg) and not from the e-liquid (0.0014 ± 0.0005 µg/mg). At the T=30 timepoint, after e-liquid formaldehyde measurements were subtracted from the puffed measurements, the resulting contribution from the aerosolization process was found to be similar to those at T=0, 0.011 ± 0.05 µg/mg, despite the T=30 puffed formaldehyde levels ranging from 0.010 to 0.049 µg/mg. For formaldehyde, adding the T=0 aerosolization values to the T=30 e-liquid measurements was found to be a good predictor for the puffed values at T=30 (r2 = 0.96). For acetaldehyde, the contribution due to aerosolization was found to increase from T=0 (0.0022 ± 0.0006 µg/mg) to T= 30 (0.0044 ± 0.0023 µg/mg). When the T=0 aerosolized values and the T=30 values are added, it resulted in an underprediction of the T=30 values by about 10%. As the collection of aerosolized carbonyl samples is labor intensive, this work suggests that direct testing of e-liquids in accelerated storage may offer a rapid screening approach for e-liquid stability.