Your chances of being affected by air pollution increase the more strenuous your activity and the longer you are active outdoors in bad air. The U.S. EPA created recommended color-coded charts that have activity guidelines for different levels of pollution. These charts can be used with the air pollution numbers reported from the U.S. embassy in Delhi (the AQI). If you are looking at air pollution measurements from other sites, pay particular attention to the numbers for particulate matter (PM : PM 2.5 and PM 10) as these are the most concerning to health. You can convert these PM numbers into an AQI number so that you can use the EPA color-coded charts.
The right mask can provide protection from the harmful health effects of breathing in bad air. But you have to wear it, it has to fit right (meaning that there be no gaps to allow outside air in), and it has to have the right type of filter and fabric to be effective.
High quality air filters can filter the air of harmful air pollution in closed rooms. Many factors play into the success of these products, including the technology of the product, the size of the room it needs to filter, the pollution load in the air and the cleanliness of the internal filter pieces.
There are many organizations in Delhi that focus on cleaning up the air and increasing awareness of air quality in the region and country. Contact them to see how you can get involved!