These are the 10 cities with the worst air pollution throughout September 2023, with Tangerang topping the list.

A recent report from Nafas, an air quality monitoring application, indicates that Tangerang had the worst air pollution in Indonesia throughout September 2023.

Air pollution levels in Tangerang were calculated based on particulate matter (PM) 2.5 pollution levels. The area recorded an average PM2.5 concentration of 57 micrograms per cubic meter.

According to the World Health Organization (WHO), the ideal air quality standard has a PM2.5 concentration weight between 0 and 5 micrograms per cubic meter.

Based on the United States Environmental Protection Agency (US EPA) air quality index, a PM2.5 air pollution level in the range of 0-12 micrograms per cubic meter signifies good air quality, while the range of 12.1-35.4 micrograms per cubic meter indicates moderate air quality, and the range of 35.5-55.4 micrograms per cubic meter indicates unhealthy air quality for sensitive groups.

Furthermore, unhealthy air quality is in the range of 55.5-150.4 micrograms per cubic meter, very unhealthy air quality is in the range of 150.5-250.4 micrograms per cubic meter, and hazardous or toxic air quality has a range exceeding 250.4 micrograms per cubic meter.

Referring to this index, the air quality in Tangerang is classified as unhealthy. In addition, one other city in September 2023 fell into the unhealthy category: South Tangerang, with an average PM2.5 concentration of 56 micrograms per cubic meter.

Nafas's Co-founder & CEO, Nathan Roestandy, stated that September was a month filled with festivities, with numerous large-scale outdoor events, including music festivals and sporting events.

Generally, Nathan continued, the average monthly pollution level in September 2023 showed a slight decrease compared to the previous month. "However, pollution spikes still routinely occur in various regions daily. This means that air quality has not truly improved," said Nathan, as quoted from the report.

The following are the 10 cities with the highest PM2.5 air pollution levels in September 2023:

1. Tangerang: 57 micrograms per cubic meter (unhealthy)
2. South Tangerang: 56 micrograms per cubic meter (unhealthy)
3. Bogor: 48 micrograms per cubic meter (moderate)
4. Bekasi: 48 micrograms per cubic meter (moderate)
5. Bandung Raya: 48 micrograms per cubic meter (moderate)
6. Depok: 45 micrograms per cubic meter (moderate)
7. DKI Jakarta: 44 micrograms per cubic meter (moderate)
8. Semarang: 39 micrograms per cubic meter (moderate)
9. Yogyakarta: 38 micrograms per cubic meter (moderate)
10. Malang Raya: 37 micrograms per cubic meter (moderate)

Nafas also reported that in September, there were times when the Jabodetabek area enjoyed fairly good air quality during the afternoon.

According to Nafas's monitoring, the lowest average hourly PM2.5 concentration during these periods of fairly good (moderate) air quality occurred in the afternoon, ranging from 22-26 micrograms per cubic meter between 11:00 AM and 5:00 PM.

"With the average hourly PM2.5 concentration varying, and aided by wind speeds of 7-10 meters per second, the Jabodetabek sky during these times appeared quite clean and a clear blue," stated Nafas in its report.