## 1 State of the Art
Among those mentioned, according to the US Environmental Protection Agency, the most-used models belong to the following categories: photochemical, dispersion and receptor models. Although air quality modeling has evolved rapidly, there are still problems in its application, caused by limiting factors such as unusual emissions or meteorological factors [16; 17]. In this regard, a series of patents have been published in Romania referring to devices for air purification and salinization [18], methods for reducing pollutants in industrial fine gases by combining ionizing radiation with non-ionizing radiation [19] or with fine water droplets [20], methods for determining the tritium concentration in the air [21], or wet desulfurization of waste gases [22]. Internationally, there are several patents in the field of air quality, and some include methods for the real-time monitoring of suspended particle concentrations [23], removal of air pollutants [24], or fusing of fire sensors [25], while others refer to monitoring systems based on improved chemical spectrophotometric sensors [26] or automatic air sample analysis [27]. Based on all aspects previously mentioned, it is generally agreed that air quality monitoring is extremely important to prevent damage to environmental quality and human health and to improve air quality as well [28; 29]. The purpose of this work was to prove that even though the air quality indicator measurements are under the maximum allowed concentrations, according to the environmental standards, there are remaining high risks in the case of children's exposure to certain pollutants. To our best knowledge, this is the first study in Romania that considers 11 years of air quality measurements, based on which an integrated approach to impact, risk, and health hazard assessments are developed. Having all these aspects in mind, the objectives of this paper were (1) to evaluate, over the last 11 years (2011-2021), the air quality of four cities in Romania, considering the daily measurements of three monitoring stations in each city for three pollutants: PM\({}_{2.5}\), As, and CO, (2) to assess the air quality using the air pollution index, and (3) to assess the impacts, risks, and health hazards. Depending on the toxicological effects and the major impacts on human health, three different pollutants were selected, namely, one in the form of gas (CO), one in the form of dust (PM\({}_{2.5}\)), and one heavy metal (As), all of them with high toxicity. Suspended particles are very dangerous (especially PM\({}_{2.5}\)), managing to penetrate deep into the respiratory system, thus causing major health problems, such as cancer and cardiovascular or neurodegenerative diseases, as well as playing a role in viral infections. Current data claim that there are approximately four million deaths caused by cardiopulmonary diseases, with the inhalation of PM\({}_{2.5}\) as the triggering factor. One of the most recent studies published in 2022 describes the mechanisms and pathways of PM\({}_{2.5}\), as well as the toxic effects of this pollutant, along with the causal associations between health and suspended particles [30]. Arsenic, an inorganic priority pollutant with high toxicity, can be found among the finest particles of PM\({}_{2.5}\) and has carcinogenic effects. At the same time, heavy metals can bioaccumulate in the human body, and they have a low degradation potential and a high degree of toxicity. One of the latest studies draws attention to the high potential of this pollutant to cause cancer and highlights the negative effects on the digestive and cardiovascular systems, as well as DNA [31]. In the case of carbon monoxide, among other negative aspects, it is well-known for its destructive effects on the atmosphere, contributing to global warming. The toxicity of this pollutant consists in its reaction with hemoglobin, which results in carboxyhemoglobin, causing serious health problems, including poisoning and even death from hypoxia [32].