Rio Branco appears this Tuesday (6) as the third city in the country with the worst air quality among the Brazilian cities listed by the IQAir platform. The capital of Acre is behind Manaus (AM) and Porto Velho (RO), which occupy the first two positions in the ranking. All three are from the North region.
According to data from the platform, the Air Quality Index (AQI⁺) in the capital of Acre is 59, with PM2.5 as the main pollutant. The platform's forecast is for the index to reach 61 throughout the day.
⏩ Based on WHO recommendations on exposure to polluted air, the Air Quality Index (AQI) is an international scale designed to help monitor air pollution in various countries by bodies and authorities. The AQI has six levels, ranging from “good” to “dangerous”.
😷PM2.5 is made up of very small particles suspended in the air, with a diameter of up to 2.5 micrometers. Because of their size, these particles can be inhaled and reach the deepest parts of the respiratory system.
The platform's guidelines include reducing outdoor exercise, keeping windows closed to prevent the entry of contaminated air and, in outdoor environments, wearing a mask. IQAir also recommends that sensitive groups use an air purifier.
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Rio Branco is the 3rd city in the North with the worst air quality — Photo: Aline Nascimento/ g1 AC
AQI Index
The AQI uses three measures to classify concentrations:
Parts per million (ppm) by volume
Parts per billion (ppb) by volume
Microgram per cubic meter (µg/m3) of air
These units of measurement are used to express the concentration of very dilute solutions. Through their detection, the AQI expresses pollution levels, which start at zero and can exceed 300.
Legend with the colors associated with each level of air pollution on the AQI scale — Photo: Reproduction/World Air Quality Index
0 to 50 – good
Satisfactory air quality, with little or no health risk.
51 to 100 – moderate
Acceptable air quality, however for some pollutants there may be a moderate health problem for a very small number of people sensitive to air pollution.
101 to 150 – unhealthy for sensitive groups
Members of sensitive groups may suffer health effects. However, the general public is not affected.
151 to 200 – unhealthy
Everyone can start to feel health effects. Members of sensitive groups may suffer more serious effects.
201 to 300 – very harmful
The entire population is more likely to be affected.
From 300 – dangerous
Everyone can suffer more serious health effects.
Fires in September
The scenario occurs amid an increase in fires in Acre. Data from the National Institute for Space Research (Inpe) show that the state registered 877 outbreaks in September, a number 80% higher than that recorded in August, when 487 were recorded.
In comparison with September 2025, when the state had 840 outbreaks, there was an increase of 4.4%. In September of this year alone, Acre recorded more outbreaks than it had accumulated in the first eight months of 2026. Between January and August, there were 584 occurrences.
The period with the highest concentration of fires in the Amazon region usually occurs between August and October, when there is a reduction in rainfall and an increase in cleaning practices in areas using fire.
Among the municipalities in Acre, Rio Branco was the third with the highest number of outbreaks in September, with 84 records. Feijó led the ranking, with 165, followed by Tarauacá, with 153.
The two municipalities together concentrated 318 outbreaks, around 36% of the total registered in the state that month.
The increase in outbreaks came after months of low numbers in Acre. There were two registrations in January, two in February, none in March and two in April. From May onwards, the numbers began to rise: there were 15 outbreaks that month, 20 in June, 56 in July and 487 in August.
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