During pregnancy, especially is you suffer morning sickness, it is easy to find yourself even more sensitive to unwanted smells and fumes. However, what's dangerous and what's just plain annoying?

Tobacco smoke
PUSH Maternity
Smoking during pregnancy has been known to affect increased chances of a baby dying of cot death. However, it is also not healthy for you or your baby to be around other people who are smoking.
If someone else who lives in your house smokes, they should be encouraged to smoke outside the home, not just in another room. It's good practice for them, as the problem could be even more dangerous for a new baby than it is for you when you are pregnant.
Don't worry about times when you are waiting at a bus stop and someone is smoking. Unpleasant as it can be, it is not a level of exposure that can cause you harm.
However, if you work in a smoky environment (eg a bar), you should seriously think about changing your job or putting your case to your employer.
The law today protects workers from secondary smoke inhalation, but in many bars, this still just means asking people not to smoke right by the bar, while they can, a few feet away from it. Obviously this will change when the full smoking ban comes in next year.
See below for more on air pollution and your job.

Paint fumes
These days, most of the harmful ingredients which used to make even regular housepaint a potentially deadly hazard, have been removed. This makes it safer to choose paints for your nursery, and also a lot more pleasant to do a spot of decorating yourself during pregnancy.
The fumes will not reach your unborn child. However, paint fumes are strong and heady, and may easily bring about an unexpected dizzy spell which could result in a fall.
Nausea is never pleasant, and if you are in the later stages of pregnancy, an episode of vomiting could make you dangerously unwell.
Try to be away from rooms or places where there is the strong smell of paint, and to keep your space well ventilated, even in winter.
Avoid paint strippers altogether, which can contain harmful chemicals.

A lack of fresh air
Tests have not found a link between regular daily contact to pollution such as city traffic and any harm to the unborn baby. Indeed, even when it is bad enough to make the mother feel sick, it does not seem to have been passed on to the baby.
However, as above, you may feel dizzy or nauseous, because breathlessness and a heightened sense of taste and smell can mean that you notice the lack of quality oxygen in the air you are breathing.
Think about your route to work. Is there a back route that may be a little longer but is not so busy with traffic? Or a route through a park, which you could at least take to work, if not on your way home when it might be dark.
Always carry a small bottle of water, so you can revive yourself even if fumes make you feel sick.
In your work, on a bus or even in your home, try to keep fresh air flowing through the place. Don't be afraid to incur the wrath of less healthy types who moan about a draught - you and your bump deserve fresh air!
If you are for some reason staying or living in an area with bad air problems, try to find other ways to keep the air fresher. Try an ioniser (you can get some quite small models now that look more suitable for lounges and bedrooms, than the old office-style models.) Pharmacists or homeware stores should stock these.
Have plenty of plants around the place. These help take the bad stuff out of the air and put back some valued cleaner air!

Air conditions at work
Whether or not you are pregnant, the law is on your side when it comes to a healthy working atmosphere.
The Health and Safety Executive feature valuable, downloadable information on the HSE website about safe working for expectant and breastfeeding mothers.