3.1. FINE AND COARSE PARTICULATE MATTER
Table 1 presents the concentrations of PM2.5 and PM2.5−10, including the mean, median, maximum, and minimum values obtained at the collection site in Canela (S1) and Gramado (S2) between April 2021 and April 2022. It was observed that the mean concentrations obtained for both PM2.5 and PM2.5−10 were higher for the municipality of Gramado compared to Canela. The results demonstrated that five samples of PM2.5 and six samples of PM2.5−10 were not in accordance with the air quality guidelines established by the WHO.
Table 1
Mean, median, maximum, minimum, and observed concentrations of PM2.5 (µg m-³) and PM 2.5-10 (µg m-³) in Canela and Gramado from April 2021 to April 2022
|
Period
|
Canela (S1)
|
Gramado (S2)
|
Parameter
|
|
PM2.5
|
PM2.5−10
|
PM2.5
|
PM2.5−10
|
WHO
|
|
15
|
60
|
15
|
60
|
CONAMA 491/2018
|
|
60
|
120
|
60
|
120
|
|
Apr 21
|
-
|
-
|
6.15
|
9.69
|
May 21
|
0.23
|
9.92
|
-
|
-
|
Jun 21
|
2.81
|
1.04
|
-
|
-
|
July 21
|
10.78
|
7.91
|
8.33
|
8.26
|
Aug 21
|
10.44
|
5.56
|
9.29
|
5.87
|
Sept 21
|
5.40
|
5.48
|
6.67
|
11.62
|
Oct 21
|
18.41(*)
|
24.44
|
21.20(*)
|
2.51
|
Nov 21
|
-
|
-
|
5.17
|
61.81(*)
|
Dec 21
|
21.52(*)
|
35.08
|
102.50(*)(#)
|
145.85(*)(#)
|
Jan 22
|
5.14
|
2.76
|
1.39
|
112.50(*)
|
Feb 22
|
9.10
|
7.44
|
12.51
|
163.90(*)(#)
|
Mar 22
|
0.36
|
5.71
|
12.19
|
150.01(*)(#)
|
Apr 22
|
6.43
|
3.93
|
21.31(*)
|
120.84(*)(#)
|
Mean
|
|
7.23
|
8.48
|
18.79
|
72.08
|
Median
|
|
5.91
|
5.63
|
9.28
|
61.81
|
Maximum
|
|
21.52
|
35.08
|
102.50
|
163.90
|
Minimum
|
|
0.23
|
1.04
|
1.39
|
2.51
|
Number of samples
|
|
11
|
11
|
11
|
11
|
Legend: (*) Values above WHO limits; (#) values above CONAMA 491/2018 limits |
Source: Authors (2023) |
No significant differences were observed in the mean values of PM2.5 (t=-0.108; p = 0.915) and PM2.5−10 (t=-1.98; p = 0.82) when comparing the two municipalities using the t-test for independent samples.
The highest concentrations of PM2.5 were reported in December 2021 in Canela (21.52 µg m−³) and Gramado (102.50 µg m−³), exceeding the air quality standards recommended by the WHO guidelines (15 µg m−³). Although the Brazilian legislation (CONAMA 491/2018) establishes less restrictive conditions (60 µg m−³), the WHO global air quality guidelines, updated in 2021, provides new evidence-based standards concerning the health effects of air pollution (WHO, 2021).
High concentrations were also recorded in Canela (S1) and Gramado (S2) in October 2021. Such periods (October and December) comprise the time when major events of the cities take place: Natal Luz (Gramado) and Sonho de Natal (Canela), which occurred between October 2021 and January 2022. These festivities were estimated to attract over 3.7 million visitors. In Canela, many attractions occurred in front of the Catedral de Pedra and next to the Praça João Côrrea (City Hall of Canela, 2023). The sampling site at S1 (Canela) is located approximately 300 m away from these locations, including the RS-235 highway, which serves as the main access route to the city. According to Dasgupta et al. (2020), the urban traffic and pollution issues are primarily influenced by geographic factors, as the incidence and impact of air pollution by vehicle emissions depend, among other factors, on the spatial distribution of economic activities.
The concentration of PM2.5 (18.41 µg m−³) reported for Gramado (S2) in October 2021 was observed under the incidence of prevailing winds blowing from the South to Northeast, with speeds ranging from 2.10 to 3.60 m s− 1. To the South of this location, the two main access routes to the city (RS-235 and RS-115 highways) are located, which receive significant contribution from vehicles that access the city by these highways. Alves et al. (2020) demonstrated that vehicular and industrial emissions were the primary sources contributing to the incidence of PM in the cities of São Leopoldo and Canoas/RS (Brazil), located 200 m and 60 m away from BR-116 highway, respectively. Thus, the proximity of the RS-235 and RS-115 highways may have influenced the contributions of PM observed at S1 and S2 during the periods of October and December 2021. The impacts of the presence of atmospheric particles corroborate with epidemiological studies that provided sufficient evidence for the WHO to determine that short- and long-term exposure to PM2.5 are related to negative effects on respiratory health (WHO, 2021). Additionally, Drakaki et al. (2014) revealed that atmospheric pollutants associated with vehicular traffic, such as HPAS, VOCs, and particulate matter, can cause skin blemishes, highlighting the importance of monitoring these pollutants.
Regarding PM2.5−10, 6 samples collected in Gramado (S2) between November 2021 and April 2022 showed concentrations that exceeded the values considered safe for public health according to the WHO guidelines (60 µg m−³) (WHO, 2021). Conversely, the results obtained for Canela (S1) were in accordance with the air quality standards for PM2.5−10, with the highest concentration observed in December 2021 (35.08 µg m−³). Coarse particles commonly have their origin associated with natural sources and can be generated through the resuspension of solid materials under conditions of great atmospheric stability. The transportation of PM at higher altitudes can occur over long distances, leading to pollutants concentrations at ground level, even in the absence of nearby pollution sources (Alleman et al., 2010). Alves et al. (2020) correlated atmospheric particles found in PM2.5−10 samples with natural sources associated with the Earth’s crust. However, since the sample content was not subjected to more advanced analysis, the association of these particles in this study with natural sources remains suggestive.
3.2. MICROSCOPIC ANALYSIS
The criteria for the identification and classification of particles under the microscope followed the procedures described by Dehghani et al. (2017), regarding the analysis of color and shape of particles. The shape of polymeric particles is attributed to fibers, fragments, and spheres. The colors can be varied, predominantly among them, are the colors black and blue. Figure 4 presents some of the particles analyzed under the microscope.
The atmospheric particles observed in Fig. 4a, 4b, and 4c correspond to PM2.5, while the particles identified in Fig. 4d, 4e, and 4f correspond to PM2.5−10. Most of these samples were collected in the municipality of Gramado (S2). It is observed that the atmospheric particles had an elongated shape, with a predominant black color and a lesser amount of blue and green, corroborating Agullo et al. (2021), who also identified a prevalence of black color for fibers and fragments and a significant presence of blue color in fibers.
Dyachencko et al. (2017) evaluated the composition of blue polymeric fibers using Fourier transform spectroscopy (FTIR) and found that these fibers can be made of cotton or acrylic. Although it is necessary the application of other techniques to confirms the microplastic content in the atmospheric particle samples, the result of this study suggests that the identified particles contain characteristic traces of polymeric material.
3.3. SEM AND EDS ANALYSIS
The morphological analyses were performed using Scanning Electron Microscopy (SEM) coupled with Energy Dispersive X-Ray Spectroscopy (EDS). Figure 5 shows the atmospheric particles collected in the municipality of Gramado with traces of artificial polymeric fibers and their elemental composition.
Anthropogenic activities are the primary contributors in the insertion of microplastic into the atmosphere (Abbasi et al., 2018). Among the most common sources of airborne microplastic include synthetic fabrics, tire abrasion, dust from urban areas, construction sites, waste incineration, particle resuspension, and dryer emissions (Dris et al., 2016; Prata et al., 2019).
Figure 5a shows a particle identified in S2 (Gramado). A study conducted by Li et al. (2018b) in Beijing observed these particles on a surface dust and classified them as artificial polymeric fiber composed mainly of Si and O (Fig. 5b). These particles are characteristics for being fibrous or in regular bar-shape and some of them have varied compositions, including Si, Mg and Al or Si, Al and K, indicating a mixture of minerals and fibers. In this sense, the high levels of Si and O (Fig. 5b) and the morphology of the particle demonstrate in Fig. 5a are in accordance with the findings reported by Li et al. (2018b), suggesting that this particle may be a polymeric fiber of artificial origin. Such particles represent an important fraction of inorganics, being contained in construction materials such as tiles, cement, and thermal insulation materials (Khadem et al., 2018). Thus, there may be a relationship between the identified particle and ongoing construction activities in the city of Gramado. According to the Union of the Region of Hortênsias/RS (Sinditur) the hotel sector alone, has experienced substantial growth, with the addition of over 35 thousand beds, due to the increasing number of visitors in the region (Sinditur, 2020).
Figure 6 shows atmospheric particles in Gramado that demonstrate characteristics suggestive of microplastic fibers, along with their corresponding chemical composition as identified by EDS.
Fibers are commonly found in our daily lives, including textile plastics, thermal insulation, and construction materials and suffer degradation as they are used, releasing fiber particles into the environment (Gasperi et al., 2018).
Li et al. (2018b) also developed a similar study to characterize microplastic fibers, associating the regular shape and predominant composition of C and O in these particles, in addition to small amounts of Na, Mg, Al, Si, K and Ca. Similar results were reported by Dehghani et al. (2017) corroborating with microplastic fibers that presented traces of Al, Na, Ca, Mg, and Si, in addition to C and O. The authors related the street dust as a potentially important source for the contamination of microplastics. Polymeric materials with low density are likely to be suspended and resuspended in the atmosphere by the action of winds and vehicle flow (Abbasi et al., 2018). All particles identified in Fig. 6a, 6b, 6c, 6g, and 6h had regular shapes and elevated peaks for C and O as in accordance with Li et al. (2018b) and Dehghani et al. (2017).
Liao et al. (2021) used the FTIR spectroscopy technique for the microplastic characterization, identifying about 20 types of suspect plastics with a size range of 10–300 µm. This technique is widely used and was applied to identify polymeric particles in a study on microplastics in the China region. In the present study, the size of the atmospheric particles varied approximately between 20 and 120 µm. The variability among the results of the studies from airborne microplastic may stem from the lack of standardized methods for collecting, quantifying, and interpreting data.
According to Weinstein et al. (2016), after being released into the environment, these particles continue to physically decompose into smaller particles over time, however, particles smaller than 500 µm are difficult to accurately determine when using a visual observation alone. Besides, the measurements of atmospheric microplastics using active pump sampling, like the one used in this study, are very scarce, since for this type of evaluation, most of the studies use the passive deposition method (Liao et al., 2021).
Due to the scarcity of methodologies and studies related to the concentration and dispersion of atmospheric particles that contain plastic material, this study found limitations in the records of polymeric particles. Therefore, secondary analyses are necessary to confirm the suspicion and evaluate the degradation of these particles in the environment.
Small soot spheres are formed in internal combustion engines from explosion of gaseous mixtures of air and hydrocarbons (Micic et al., 2003). A study performed by Alves (2019) in the city of São Leopoldo/RS (Brazil)identified vehicular soot in the samples. Thus, it is possible to associate the particle identified in Fig. 7a as a particle from motor vehicles, which is similar to those found in the study performed by Alves (2019). Among the factors that contribute to this occurrence, the proximity of the collection point to the RS-235 highway, which serves as an access route to the city of Gramado, can be mentioned to be favoring the appearance of this type of particle in PM2.5.
Figure 7c shows a particle in a spheric shape, recorded in PM2.5 in S2 (Gramado). Similar particles were identified by Micic et al. (2003) as a spherical agglomerate of fine fly ash particles from local power plants in the region of Belgrade, Serbia. The fly ash particles have a perfectly spherical shape, generated by the solidification of molten silicate materials in the flow of smokes and flames, and soot particles can be absorbed on their surface. Although in the region of this study there are no coal plants, atmospheric pollutants can spread across continents, especially those with little reactivity and particulate matter that depend on the atmospheric stability, topography, and meteorological conditions of the region (Guimarães, 2017). Figure 7b represents a particle found in PM2.5−10 in Canela (S1), a similar particle was suggested by Alves (2019) as coming from the Earth’s crust, having a natural origin.
It is observed that atmospheric particles identified in Figs. 5 and 6 have a different morphology when compared to atmospheric particles from known sources, such as vehicle soot and fly ash, reinforcing the indication that these particles may be polymeric particles. However, there are not enough studies to evaluate the presence of microplastics in the atmosphere of the study region.
Studies reported that the atmosphere is an important route for transporting microplastics and influences the flow of plastic pollution in other environments, such as land and sea (Bank & Hansson, 2019). Microplastic particles have already been found in urban atmosphere and in remote regions, far from any source of emission of these particles (Allen et al., 2019; Liu et al., 2019). This indicates that if the presence of plastic material is confirmed in the sampling area of this study, environments and areas close to the municipalities of Canela and Gramado may be being influenced by the presence of this material. However, systematic studies on microplastic patterns in the air are needed to understand the exposure to these particles transported in different environments.