The study looked at air pollution in big cities in India. They focused on six main pollutants that can harm people's health. The researchers wanted to see how these pollutants change over time in cities like Bengaluru, Delhi, Chennai, and Mumbai. They found that each city has different levels of pollution and the pollutants behave differently in each city. The amount of pollution changes throughout the year, following patterns we already know about. The sources of pollution can be local or come from outside the city, and this varies between cities. This shows the need for specific rules to control pollution in each city.