1) IF the smell is truly, to the average reasonable person (not just to someone who may be more sensitive to it) so bad as to render the unit uninhabitable AND you have given the landlord written notice of the issue and a reasonable amount of time after notice to cure or fix the problem and he does not (or can not), then at that time, you may withhold rent for uninhabitability. Of course, the landlord may disagree and may try to sue or evict you for unpaid rent; have the rent available (don't spend it), since if you go to court and a judge feels that the smell was tolerable, you will be forced to pay. Or to put it another way: uninhabitability is a legal reason to not pay rent, but whether a unit is uninhabitable is generally a subjective determination, so if litigation ensues, you are not guaranteed to win.2) No: if you vacate your unit while leaving it unsecured, even for what you deem good reasons (e.g. to let a smell disapate), that is *your* action, your negligence, and your responsibility, not the landlord. It is unreasonable to leave windows open in a vacant unit. You need to leave the unit secured if you are not there.a) Further, if you vacate the unit while leaving the windows open and damage is therefore caused to the unit or the landlord's building (e.g. rain gets in and wrecks a floor or wall), you would be liable for the repair costs.