Understand how the air quality index in Brazil It's not just a matter for technicians or people who work in the environment. It directly affects how we breathe every day in cities like Brasilia, São Paulo, or Rio de Janeiro, and what people with asthma, heart problems, or simply those who want to go for a run without inhaling a cloud of pollution can expect.
In recent decades, Brazil has developed a own air quality assessment structurewith national regulations, monitoring stations distributed throughout the territory, and Air Quality Index (AQI) calculation models inspired by international standards, such as those of the United States Environmental Protection Agency (US EPA) and the recommendations of the World Health Organization (WHO). There are also comparable experiences, such as the air quality index in SingaporeLet's take a closer look at how it's measured, what the values mean, what pollutants are taken into account, and how the reliability of the data is ensured.
What is the Air Quality Index (AQI/ICA) in Brazil?
The Air Quality Index, known internationally as AQI and in Brazil as Ar Quality Index (IQA or ICA)It is a simplified way of translating all the complex information about substances in the air into a single number and a health category. Instead of forcing the public to interpret micrograms per cubic meter and moving averages, the index provides a score and a label (e.g., "good," "moderate," etc.).
In the case of Brazil, this index is calculated from several key pollutantsboth in the form of particles and gases: coarse particulate matter (PM10), fine particulate matter (PM2,5), sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), tropospheric ozone (O3), total suspended particles (TSP), and, in some networks, smoke (FMC). Each pollutant is measured with a specific time resolution and then converted into a sub-index; the daily AQI value is usually the most unfavorable of these. Equivalent systems can be found in the air quality index in Ecuador.
A practical example helps to illustrate the concept: in BrasiliaIn the nation's capital, an AQI of 30 was recorded, a value that, according to the US EPA scales, is classified as "Good." This equates to a situation in which the air is considered safe for outdoor activities for the entire population, including sensitive individuals.
To arrive at that number, concentrations such as the one in PM2,5 (fine particulate matter), which in that scenario is 5,5 µg/m³, and that of PM10, also 5,5 µg/m³. In the case of gaseous pollutants, nitrogen dioxide (NO2) can be measured, for example, at around 1,6 µg/m³. Each value is compared with reference tables that establish which level corresponds to a "good", "moderate" or worse quality.
This type of index allows both authorities and citizens to have a quick tool for decision makingFrom issuing health protection warnings when there are pollution spikes to proposing temporary traffic restrictions or recommending teleworking during very severe episodes of poor air quality.
Main pollutants and their role in the Brazilian ICA
The heart of the air quality system in Brazil is made up of the regulated pollutantsThese pollutants are defined according to standards, time averages, and reference thresholds. They are not chosen randomly, but rather based on their proven impact on human health and the environment.
First, there is the inhalable particulate matter (PM10)These are particles with an aerodynamic diameter of up to 10 microns. They can originate from road dust, industrial processes, biomass burning, or vehicle emissions. For this pollutant, the WHO recommendations indicate a reference limit value. annual of 15 µg/m³ and a value of 24 hours of 45 µg/m³These figures serve as a health target and are compared with measured data to assess whether they are respected or exceeded.
El fine particulate matter (MP2,5) It is even more worrying because its particles, smaller than 2,5 microns, penetrate deep into the lungs and can even enter the bloodstream. The WHO suggests a limit annual of 5 µg/m³ and a value of 24 hours of 15 µg/m³When these levels are frequently exceeded, hospital admissions for cardiovascular and respiratory diseases increase. Cases and solutions are analyzed in the air quality in Guatemala.
Among the regulated gases, the following stand out: sulfur dioxide (SO2)SO2, which typically comes from the combustion of fossil fuels containing sulfur and from certain industrial activities. The WHO guidelines set a value of 40 µg/m³ as a 24-hour average, with the aim of reducing acute episodes of bronchoconstriction, especially in people with asthma.
El nitrogen dioxide (NO2)Closely linked to road traffic and the combustion of fossil fuels in general, it has two important references: one annual average of 10 µg/m³ and a limit of 200 µg/m³ for one houralso according to WHO guidelines. Similar problems are described in the air quality in Mexico CityHigh levels of NO2 are associated with irritation of the airways, increased susceptibility to infections, and worsening of chronic respiratory diseases.
As to carbon monoxide (CO)A colorless and odorless gas produced by incomplete combustion is subject to a limit of 9 ppm as an 8-hour moving averageIts ability to bind to hemoglobin reduces oxygen transport in the blood, which can be especially problematic for people with heart disease.
El tropospheric ozone (O3) It is a secondary pollutant: it is not emitted directly, but is formed from photochemical reactions between nitrogen oxides and volatile organic compounds in the presence of solar radiation. A reference is used. 8-hour moving average of 100 µg/m³ And, specifically for the "peak season" (the months when conditions favor ozone formation), a guideline value is considered to be 60 µg/m³High exposures cause eye irritation, coughing, and breathing difficulties.
Brazilian regulations also consider other metrics, such as Total suspended particles (TSP) or smoke (FMC), with different temporal averages. Although today the international focus is heavily on PM10 and PM2,5, these additional parameters help to better characterize the actual mix of pollutants in certain regions and times of the year.
Air quality standards in Brazil and WHO recommendations
Brazil has national air quality standardswhich set maximum permissible levels for each pollutant. At the same time, there are the WHO guidelinesThese are recommendations aimed at protecting health, often stricter than the internal regulations of many countries.
For each pollutant (such as PM10, PM2,5, SO2, NO2, CO or O3), three key elements are defined: the unit of measurement (usually µg/m³ or ppm), the average time (annual, 24 hours, 8 moving hours, 1 hour…) and the reference value. The combination of these factors determines when air quality is considered to meet or exceed the standard.
In practice, the Brazilian system distinguishes between annual averages, which reflect chronic exposure, and short-term stockings (24 hours, 1 hour, 8 hours mobile…), which capture specific episodes. Both dimensions are important: a city can have relatively low annual averages, but suffer frequent pollution peaks that are very harmful to health.
The WHO recommendations function as international benchmarksThese measures are designed to minimize health risks. Brazilian authorities use these guidelines as a basis for designing their standards and index structures, although in some cases they may establish transition periods or intermediate values.
Beyond the comparison with the WHO, it is key to understand that compliance with national regulations does not mean a total absence of risk, but levels considered acceptable according to available scientific knowledge and the country's environmental policy objectives.
How air quality data is measured, averaged, and validated
Behind every ICA value lies a network of monitoring stations distributed throughout BrazilThese stations are equipped with instruments that continuously record the concentration of various pollutants. Many of these stations are part of interactive maps where pollution levels in cities like São Paulo, Rio de Janeiro, Belo Horizonte, Salvador, and Fortaleza can be viewed in real time.
The data is collected using different methods. temporary resolutionsDepending on the pollutant. For example, in the case of smoke (FMC), 24-hour averages are used, which are then used to calculate an annual arithmetic mean. Particulate matter (PM10) is also measured as a 24-hour average, with a subsequent annual average; the same applies to PM2,5.
For sulfur dioxide (SO2), the following are used 24-hour averages for some purposes (such as calculating the ICA and verifying daily standards), while the assessment of long-term exposure uses the annual arithmetic meanTotal suspended particles (TSP) are analyzed as a 24-hour average and then summarized in a annual geometric mean, suitable for highly variable data distributions.
Ozone (O3) is treated somewhat differently, using as the main indicator the maximum 8-hour moving average obtained during the dayIn addition, to assess what is called the "peak season" for ozone (usually warm and sunny periods), a maximum moving average every 6 monthsThis allows us to detect if high levels are occurring repeatedly during those critical intervals.
Regarding carbon monoxide (CO), the following is taken maximum 8-hour moving average for each dayThis method is used both in generating the index and in verifying air quality targets. Nitrogen dioxide (NO2), meanwhile, is analyzed using a 24-hour average and an annual average, so that both very high isolated episodes and situations of chronic exposure can be detected.
In order for this data to be statistically sound and officially usable, there is a system of validation criteria from the sampling. The goal is to ensure that the published averages are not based on a few isolated measurements, but on a sufficient number of valid observations.
In the case of a half an hourIt is required that at least three-quarters of the measurements from that period be valid. For a daily averageIt is required that, at a minimum, two-thirds of the hourly averages for the day meet the quality requirements. This logic holds true when moving to longer time scales.
So, one monthly average It is only considered valid if at least two-thirds of the daily averages for the month are available and have passed the quality filters. And for the annual averagesA particularly demanding criterion is applied: there must be at least half of the valid daily averages in each of the three four-month periods of the year (January-April, May-August, and September-December). This prevents a station with many data gaps at certain times from distorting the annual assessment.
In the specific case of ozone, a further definition is established mid-seasonThis corresponds to the last six months, during which O3 formation is most likely. To validate this average, at least two-thirds of the daily moving averages for that period are required. Only when these criteria are met are the results included in official air quality assessments.
Availability of data, maps, and days that exceed the norms
The information generated by the stations is consolidated into interactive platforms and maps where you can consult, for example, the total number of days sampled over the years, the days that exceed national standards or WHO recommendations, and the distribution of these excesses by season.
Many websites allow you to choose between viewing information per individual station or across all stations in a network. This allows for comparisons between air quality in an industrial area versus a residential area or urban park, and helps identify cities or neighborhoods that require more urgent action.
The data available on these platforms typically includes maps of the monitoring stations, maps of annual air quality assessment, listings of the number of valid days per year and counts of days that exceed national standards and the WHO guidelines for each contaminant. This information can be downloaded in many cases for more detailed analysis.
Thanks to these systems, it is possible to answer questions such as how many days a year a given city exceeds the recommended PM2,5 level, or whether numerous ozone episodes have occurred in a specific period. These indicators are fundamental for designing Public policies for pollution control, assess the impact of new regulations and prioritize investments in public transport or clean technologies.
An additional element of interest is the data from urban green spacesIn the regional context, Brazil shows a value of around 55% in certain metrics related to green areas or urban parks, comparable to 55% for Bolivia, 53% for Montenegro, 40% for Suriname, 46% for Paraguay, and 65% for Uruguay. A higher proportion of green areas is generally associated with better microclimate regulation and potential improvements in local air quality.
Notice of use and limitations of air quality data
Although all this monitoring and analysis infrastructure offers a very useful overview, it is important to be clear that air quality data They are not always fully validated at the time of their publicationMany projects and platforms explicitly state that the information displayed may be modified later once all quality assurance controls have been applied.
In initiatives of global scope, such as the World Air Quality IndexIt is specified that, despite having applied all reasonable skills and care to compile and present the data, neither the project nor its team can assume contractual, extra-contractual or other liability for losses, injuries or damages that may arise directly or indirectly from the use of this preliminary information.
This means that users should understand the figures displayed as benchmark indicatorsThese data are especially useful for real-time monitoring, but not necessarily as definitive data for legal or scientific purposes. Once the review and validation processes are complete, the series may be adjusted and, in some cases, vary slightly from the initially published values.
In practice, this does not diminish the value of public consultation tools; it simply requires them to be interpreted with caution, bearing in mind that the competent bodies may update, correct or review the information without prior notice when necessary to ensure the quality of the records.
Technology and solutions to improve air quality in Brazilian cities
Beyond measuring and describing pollution, in Brazil and other countries, measures are being deployed technological solutions to improve air qualityespecially within the framework of so-called "smart cities." This involves integrating advanced sensors, data analysis, and interventions on the ground to reduce emissions and protect public health.
Some projects, such as those promoted by specialized companies, offer high-resolution air quality monitorsThese monitors are capable of measuring multiple pollutants in real time and sending the data to cloud platforms. They can be installed on streetlights, public buildings, schools, or traffic intersections, providing a hyperlocal map of urban pollution.
They are also being used drones equipped with sensors This technology is used to analyze pollution in hard-to-reach areas or at different altitudes. It is especially useful for detecting point leaks, characterizing industrial emission plumes, or assessing the impact of forest fires and agricultural burning on nearby population centers.
In busy outdoor spaces, solutions such as outdoor air purifiersThese systems employ mechanical filtration, electrostatic systems, or other technologies to reduce concentrations of particles and gases in specific areas. While they do not replace structural emission reduction measures, they can be a complement in areas with high pedestrian traffic.
The piece that articulates all of this is usually a control panel or data dashboardThis system integrates measurements from fixed stations, low-cost sensors, drones, and other sources. Through real-time visualizations, heat maps, time series data, and automated alerts, authorities can react quickly to pollution episodes and assess the effectiveness of implemented measures.
In parallel, smart city solutions are combined with more traditional strategies, such as improving public transport, electrifying fleets, promoting cycling, regulating industrial emissions, and protecting or expanding green areas and urban parkswhich help to partially mitigate the concentration of some pollutants and improve thermal comfort.
This entire network of regulations, stations, validations, and technological solutions makes the air quality index in Brazil a environmental and health management tool Very comprehensive. By knowing which pollutants are measured, how averages are calculated, what limits are used as a reference, and how the data is guaranteed, citizens can interpret pollution maps more effectively, assess health risks, and demand more ambitious public policies when pollution levels remain above recommended limits.
