Let's get some perspective. If you live in an urban area, especially a major city like London/New York/Paris/etc, then second hand tobacco smoke is the least of your concerns regarding what your children are inhaling. Most towns and cities around the globe, including in the West, have pollution levels far above international standards that are considered safe. Me and my wife are well aware of this. It's safer for my children to be around smokers 24/7 and live in the countryside than it is for them to live in a city with non-smoking parents.
Citation please
at least in North America, air pollution in cities are way below international and national standards (some exceptions, but usually in remote regions, for a variety of reasons), per the EPA and Environment Canada.
Moreover, those pollutants are *usually* the fault of dust from unpaved roads, heat-induced ozone concentration, or forest fire smoke.
Air quality, at least in in North America (but probably in the rest of the Western world, with exceptions) has been steadily improving for the past 20 years