How can outdoor pollution affect the air quality indoors?

How can outdoor pollution affect the air quality indoors?

The main cause of indoor air pollution is inefficient fuel combustion from undeveloped technologies used for cooking, heating and lighting. There are also natural indoor air pollutants, like chemical pollutants from building materials and cleaning products. However, outdoor air pollution can be a great contributor to indoor pollution, especially in highly ventilated homes or homes near pollution sources. Similarly, indoor air pollution sources may also cause outdoor air pollution, especially in cities where many homes use biomass fuels or coal for heating and cooking.