Products of Lead(II) nitrate decomposition
Check if the green condensate is $\ce{N2O3}$. It has been reported to be blue-green.
In the presence of water vapor and oxygen, the nitrogen dioxide that you are trying to obtain is in equilibrium with nitric acid and nitrogen trioxide, as explained here.
As reported in the Journal of Industrial and Engineering Chemistry, volume 12, number 6, page 531-538 (1920), condensation of gaseous nitrogen dioxide in a spiral condensor at -5 °C in the presence of oxygen and water vapor resulted in liquid with distinct upper and lower layers, the upper layer being a concentrated nitric acid layer (essentially no water) and the lower layer being a diluted nitric acid layer (27 %) water.
So the reason you are getting side products is likely that water vapor and oxygen are also present and causing equilibrium reactions that yield nitric acid, nitrous acid and nitrogen trioxide.
Reference

CCXIV.—The dissociation of gaseous nitrogen trioxide, Bernard Mouat Jones,  J. Chem. Soc., Trans., 1914, 105, 2310-2322, DOI: 10.1039/CT9140502310