**1. Introduction**

Pollutant refers to chemical substances, particles, or toxic gases, introduced into the environment from various sources and that cause adverse effects to living beings and the ecosystem, compromising the soil, water, and atmospheric air. Atmospheric

pollution, in turn, can be defined as any form of matter in quantity, concentration, time, or other characteristics, which make or may make the air unsuitable or harmful to health, inconvenient to public welfare, harmful to fauna and flora, or environmental safety. Air pollution is one of the biggest environmental threats to human health, a condition related to human development activities and climate change agenda. In 2021, the World Health Organization (WHO) listed the improvement of air quality within the top 10 health challenges of the year.

The primary sources of air pollutants are anthropogenic, which originate from processes carried out by industries, mining, transport, and construction. Also, pollutants are classified as mobile sources, which include most forms of transport, such as automobiles, trucks, and planes, or fixed sources, such as industrial and housing facilities. Another form of classification is to determine the pollutants that are emitted directly by polluting sources, called primary pollutants, such as particulate matter (PM), sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), or those that result from interactions with the environment, called secondary pollutants. Among the air pollutants mentioned, PM is the pollutant that has received greater emphasis in scientific research, both in epidemiological and experimental studies.

The term PM refers to a mixture of solids and liquid droplets suspended in the air [1] classified as large "coarse" particles (PM10; particles with a diameter less than 10 μm). PM10 represents mainly the overall mass of PM and can be derived from numerous sources, such as silica-based crustal particles (e.g., soil, sand, and volcanic ash), burning of natural materials (e.g., woodsmoke), or wear of machinery (e.g., vehicle braking and tire erosion). "Fine" PM (PM2.5: particles with a diameter less than 2.5 μm) and "ultrafine" PM (PM0.1: particles with a diameter less than 100 nm) are generally derived from industrial burning of fossil fuels and traffic-related sources [2]. PM is primarily generated by fuel combustion in different sectors, including transport, energy, households, industry, and agriculture. In 2013, the outdoor air pollution and PM as carcinogenic by the WHO International Agency for Research on Cancer (IARC) [3].

The size of inhaled particles is inversely correlated to their potential to cause health problems. Small particles, less than 10 μm in diameter, are the most significant problems because they can penetrate deeply into the lungs, and some particles can reach the bloodstream [4]. The health risks associated with PM equal or smaller than 10 and 2·5μm in diameter (PM10 and PM2·5, respectively) represent a particular public health relevance. Both PM2·5 and PM10 can penetrate deep into the lungs, but PM2.5 can even enter the bloodstream, primarily resulting in cardiovascular and respiratory impacts and affecting other organs.

In 2005, the guidelines established by the WHO for PM2·5 concentrations went from 65 to 25 μg/m3 during the 24-h period and from 15 to 10 μg/m3 during the period one year [5]. However, guidelines may be different in each country. For example, in Brazil, the final air quality guidelines were established by CONAMA resolution No. 03 /90, updated in Resolution No. 491, of November 19, 2018, which provides for air quality standards. Considering the levels of fine particulate matter (PM2·5) of 25 μg/ m3 for the 24-h period and 10 μg/m3 for the annual average, the same was indicated by the WHO [6].

In 2021, the WHO released the update of air quality guidelines based on the extensive scientific evidence currently available identifying the levels of air quality necessary to protect public health worldwide. The updated WHO Global Air Quality Guidelines (AQGs) provide recommendations on air quality guideline levels and interim targets for six key air pollutants. Moreover, for PM, there was a significant

*Environmental Particulate Air Pollution Exposure and the Oxidative Stress Responses: A Brief… DOI: http://dx.doi.org/10.5772/intechopen.101394*

reduction in the recommended levels. For PM2·5, the standard established for the annual average 15 years ago was reduced by half, from 10 to 5 μg/m3 , and concerning the exposure in the 24 h, the parameter was reduced from 25 to 15 μg/m3 . About PM10, in the annual average, it reduced from 20 to 15 μg/m3 and the 24-h period values were reduced from 50 to 45 μg/m3 [7].

To achieve these goals, the WHO has set interim targets that serve as incremental steps in the progressive reduction of air pollution toward the air quality guideline levels and are intended for use in areas where air pollution is high. These levels could be used by authorities in highly polluted areas to develop pollution reduction policies that are achievable within realistic time frames [7].

According to the IQAIR website [8], the 15 most polluted cities in the world, considering only PM2.5, are located in China or India (87% are Indian cities). The city of Hotan in China was the "champion" in 2020, with an annual average of 110.6ug/m3 of pollution by PM2·5. China and India are part of the BRICS, a group formed by five large emerging countries—Brazil, Russia, India, China, and South Africa—representing about 42% of the population, 30% of the territory, and 18% of trade worldwide. In the air pollution ranking, South Africa is classified in 49th place, Brazil in 68th and Russia in 86th, with an annual average of 18.0, 14.2, and 9.3 respectively in 2020, which is considered moderate (South Africa and Brazil) and good air quality for Russia, considering the new WHO guidelines [8].

The assessment of environmental data allows us to understand the economic, social, and environmental impact of pollution in both developed or developing countries, and it is crucial for planning to reduce air pollution activities. Since air pollution can affect our health in various ways, depending on the exposure time (short or long term), type of pollutant, concentration of polluting agents, age group, and prior health condition. In this way, a study published in 2017 described ambient PM2·5 as the fifthranking mortality risk factor in 2015. Exposure to PM2·5 caused 4·2 million deaths and 103·1 million -adjusted life-years (DALYs) in 2015, representing 7·6% of total global deaths and 4·2% of global DALYs, 59% of these in the east and south Asia. Deaths attributable to ambient PM2·5 increased from 3·5 million in 1990 to 4·2 million in 2015. These deaths occur mainly due to stroke, heart disease, lung cancer, and chronic respiratory diseases [9]. Liu et al. [10], demonstrated in a study that evaluated particulate air pollution and daily mortality in 652 cities that an increase of 10 μg/m3 in the 2-day moving average of PM10 concentration was associated with increases of 0.44% in daily all-cause mortality, 0.36% in daily cardiovascular mortality, and 0.47% in daily respiratory mortality. The corresponding increases in daily mortality for the exact change in PM2·5 concentration were 0.68, 0.55, and 0.74%, respectively. Evidencing an independent association between short-term exposure to PM10 and PM2·5 and daily all-cause, cardiovascular, and respiratory mortality in more than 600 cities across the globe, reinforcing the evidence of a link between mortality and PM concentration established in regional and local studies [10].

Studies have described particulate pollution exposure to various problems, including premature death in people with heart or lung disease; non-fatal heart attacks; cardiac arrhythmia; asthma; decreased lung function; increased respiratory symptoms such as airway irritation, coughing, or difficulty breathing. People with heart or lung disease, children, and older adults are most likely to be affected by exposure to particulate pollution [11]. In addition, sensitive groups (also called at-risk populations)—A term used for a category of people at increased risk of experiencing adverse health effects related to exposure to air pollution, may be at increased risk due to intrinsic (biological) factors, extrinsic factors (external, non-biological), increased

exposure and increased levels of air pollutants. Thus, the severity of the health effects experienced by the sensitive groups may be greater than in the general population [12]. Therefore, the establishment of air quality standards in large cities has contributed to estimates of data that helps environmental management and community health. In parallel, many laboratories are carrying out research that emphasizes the mechanisms by which exposure to air pollution impacts human health, thus alerting the need to develop public health policies and stricter air quality standards.
