It’s the rainy season, Why is Air Quality Worse than Last Year?

This is the first blog in our 2021 Insight Series, a 10 part deep dive into air quality insights that the Data Science Team at Nafas discovered over the course of 2021. 

Enjoy our first insight and stay tuned for the rest!


December, according to Nafas’ data, was the best month in 2020 with an average AQI of 63 (this means air quality was in the green!). Wind speed and rain have a great influence on the AQI. The month with the greatest wind speed in 2020 was December, and the rain intensity was also classified medium to high at that time. As a result, the average AQI for December 2020 was Good, making it the best month of the year. Our team expected the same thing to happen in 2021, we expect the same amount of wind and rain in December 2021 as in December 2020 In reality, the data showed the opposite. The air quality was substantially worse during certain times in the day throughout December 2021, as shown in the graph below.

How can this happen? What makes the air quality in December 2021 much worse than in 2020?


Using the 24-hour average air quality chart for December 2020 and December 2021, the graph reveals that air quality in December 2021 is around 47% worse than it was in December 2020. We discovered two significant factors that have a significant influence on this drastic change:

  1. We know that wind has a big impact on air quality; the greater the wind speed, the better the air quality, and the lower the wind speed, the smaller the impact on air quality. According to our data, the average wind speed in December 2021 was lower than in December 2020, which explains why our air quality in December 2021 was poorer than in December 2020.
  2. We also know that rain has an influence on air quality.* Higher rain intensities have a better probability of improving air quality, whereas low rain intensities or no rain have little effect on air quality. Rainwater has the power to wash away our pollutants and lower the average AQI. According to our data, the rain intensity in December 2020 was greater than in December 2021. This can potentially explain why our air quality was worse in December 2021 than it was in December 2020.

    *more research on the impact of rain on air quality needs to be done in Indonesia to ensure that this hypothesis is applicable in all cases of rain impacting air quality


In Conclusion, due to two key climatic events, air quality was worse in December 2021 than it was in December 2020. We discovered that different levels of rain and wind have distinct effects on air quality. If the rain intensity was low and the wind speed was high, the air quality may be improved. If the rain intensity was high and wind speed was high it would help improve air quality. The air quality may also improve when there is a lot of rain and low wind speed, although this is not always the case. However, because rain intensity and wind speed were both low in 2021, air quality did not improve, therefore the average AQI in December 2021 was higher than December 2020.

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