Data validation has shown that the results are valid. Table 2 presents all of the model's required indicators. The results provided were obtained using a data analysis that has been thoroughly discussed in other literature (Asl et al., 2018, Bonyadi et al., 2020a, Miri et al., 2016). The daily and annual standard values for PM2.5 is 35 μg/m3, and 15 μg/m3, respectively, according to the U.S. EPA-National Ambient Air Quality Standards (NAAQS) (Liang and Su, 2009). Furthermore, the WHO Air Quality Guidelines for PM2.5 are 5 μg/m3 per year and 15 μg/m3 per day (WHO, 2021). The Department of Environment Islamic Republic of Iran follows and implements the U.S. EPA-NAAQS for criteria air pollutants. Table 3 depicts a summary of RR, AP, and the number of excess cases in 2018 and 2019 for PM2.5 effects on human health as determined by the AirQ software. The results showed the average annual concentration of PM2.5 were 31 μg/m3 and 26 μg/m3 during the 2018 and 2019 years, respectively, which were 2.06 and 1.73 times greater than NAAQS. These results demonstrate that PM2.5 has an undeniable impact on all-cause mortality and annual additional cases from short-term exposure to PM2.5. Several studies have shown that PM2.5 adversely affects human health at concentrations below current air pollution standards. This suggests that existing guidelines may not provide adequate protection from a public health perspective(Asl et al., 2018, Ozcan, 2012). For every 10 μg/m3 rise in PM2.5 concentration, the relative risks of PM2.5 were calculated and the results for the 2018 and 2019 years included the lower (5%), central (50%), and upper (95%) classes of RR (as seen in Table 3). According to the median relative risk to this factor, the RR of mortality increases by 1.5% for every 10 μg/m3 rise in PM2.5 concentration. In Table 3, the estimated AP of total mortality attributable to PM2.5 was 3.11% and 2.37% in 2018 and 2019, respectively. Moreover, the estimated number of excess cases of PM2.5 were 339.7, and 264.4 in 2018 and 2019 years, respectively. The estimated AP for the cumulative number of total mortality and different PM2.5 concentrations, with lower, central, and upper categories in 2018 and 2019 years, has been shown in Fig. 2 and Fig. 3, respectively. The findings in Table 3, Fig. 2, and Fig. 3 show that PM2.5 concentrations in both 2018 and 2019 years had a greater effect on the total number of deaths.
These results are in line with the study conducted by Bahrami Asl et al. (Asl et al., 2018) who reported that the estimated AP for the total number of mortality attributable to PM2.5 in Hamadan, Iran was 4.42, and the corresponding estimated number of excess cases was 131.9, which led to cardiovascular and respiratory mortality rates. Also, Bonyadi et al. (Bonyadi et al., 2020b) stated that the yearly mean PM2.5 concentration in Shiraz, Iran was 14.35, and 16.45 μg/m3 in 2016 and 2017 years, respectively. In the 2016 and 2017, there were 25 and 20 cases, respectively, of acute myocardial infarctions (AMIs) related to PM2.5. In addition, Hadei et al., (Hadei et al., 2020) reported that the average yearly PM2.5 concentrations in 25 Iranian cities were 1.5–6.1 times greater than the WHO's guideline value of 10 μg/m³ with 13,321 cases of death (95% C.I.: 8837 – 17378) ascribed to it each year. In the other study, Sicard et al. (Sicard et al., 2019) stated long-term exposures to outdoor O3, PM10, and PM2.5 have significantly increased mortality and hospitalizations in a number of cities of Iran, Italy, and France in 2014–2019. Moradi et al. (Moradi et al., 2022) perused the concentrations of PM2.5 in Ardabil, Iran (2018), and found that the annual average PM2.5 concentration was 15.47 μg/m3. In Isfahan, the annual average PM2.5 concentration in 2018 and 2019 was 31 and 26 μg/m³, respectively. This is greater than the finding of Harvard University researchers who studied PM2.5 in six American cities, and found that the pollutant's yearly average concentration was 18 μg/m³ (Dockery et al., 1993). A lower PM2.5 concentration was connected to a lower death rate, according to a different United States study. Likewise, it was shown that 2732 additional mortality would be expected for every 10 μg/m3 rise in the average PM2.5 concentration (Laden et al., 2006). A review of studies on the effects of frequent or short exposure to pollution in two industrial cities in northern Italy found PM2.5 as one of the 177 pollutants assessed annually for a population of 24,000 caused the most deaths at 4.5% imputed share, 8 deaths (Fattore et al., 2011). Hopke et al. (2018) studied at the PM2.5 concentrations in 10 significant Iranian cities from 2013 to 2016 and discovered that they were all over the WHO Air Quality Guideline value on an annual average (Hopke et al., 2018). However, as the values measured at the sampling points reflect average human exposure, setting additional sampling points at various locations may increase the credit of the outcomes and the practicality of the associated health risk assessment.
Table 2. Statistical parameters required for models to estimate mortality attributed to PM2.5.
Year
|
Data
|
Concentration (μg/m3)
|
2018
|
Annual
Winter
Summer
|
Mean
Maximum
Mean
Maximum
Mean
Maximum
|
31
166
37
117
26
166
|
2019
|
Annual
Winter
Summer
|
Mean
Maximum
Mean
Maximum
Mean
Maximum
|
26
80
29
80
24
72
|
Table 3. Estimated AP and number of extra cases per year caused by short-term PM2.5 exposure.
Year
|
Health Endpoint
|
Relative Risk
|
Estimated
AP (%)
|
Estimated
number of
excess cases
|
2018
|
Total Mortality
|
Lower
Central
Upper
|
2.3053
3.1175
3.9163
|
251.2
339.7
426.8
|
2019
|
Total Mortality
|
Lower
Central
Upper
|
1.7514
2.3731
2.9871
|
195.1
264.4
332.8
|