Table 2.

Conversion Fraction of ISOPOOH to HCHO in ISAF.

Room Temperature Measurements	Conversion fraction	Estimated Uncertainty*
(1,2)-ISOPOOH, dry	0.03	0.04
(4,3)-ISOPOOH, dry	0.06	0.03
(1,2)-ISOPOOH, humid	0.06	0.02
(4,3)-ISOPOOH, humid	0.10	0.04

^*The uncertainty was conservatively estimated using data without applying the pre-instrument conversion correction. The ratio of the HCHO data / ISOPOOH data, both background-subtracted, was plotted for each experiment. The highest value of the ratio, taken as a mean for each data section selected for the conversion fits (red dots in Fig. 3, top panel), was determined for each experiment and was averaged if there were two of that experiment type. For the dry experiments, the uncertainty was set to the difference between the highest value and the fit value. For the humid experiments, the uncertainty was taken as twice the difference.