1. Meteorological departments in many countries or regions will provide information about the number of blue sky or air quality index. You can log on to official website of the Meteorological Department or use their mobile phone application to get the latest blue sky data.
2. Environmental protection departments or similar institutions in some areas will also provide data on air quality and blue sky numbers. You can log on to the official websites of relevant departments or consult their information centers to obtain relevant data and reports.