In my world, the humans left Earth a few centuries ago because it was too heavily polluted with chemical smog. They've settled a new planet and have so far managed to keep it clean. However, they are looking to restore the Earth and conduct periodic checks on its health and the state of the chemical pollution.
The current situation is this. The last check on Earth revealed that the chemical pollution is now negligible. So, the humans filled up a spacecraft with supplies, a team of 10, and enough fuel to get to Earth. However, these astronauts get there, land, and soon discover that they're not safe: although the chemical pollution is less potent, one of their number drops dead after a few days from chemical poisoning. The chemical smog is a mixture of a few chemicals: primarily carbon monoxide, with some vaporised phosgene and (just for variety) some LPS.
The question now is how the remaining 9 could survive until their rescue ship arrives in a years' time, given a 5-4 split of women to men and anything from the 21st century that might have survived on Earth. Assume they know their way around and have enough skilled people that they can use any method of transport; additionally, they have brought a 21st century nuclear fission reactor with them for power. Their ship can support them for 5 days each month before the oxygen runs out and needs to recharge.
What methods could they use to avoid chemical poisoning?