3.2 Elemental Concentration
The elements linked to PM2.5 concentrations in Faridabad, Haryana, India, between July 2022 and July 2023 are shown in Fig. 2. During the entire period of sampling, 41 elements (B, Na, Mg, Al, P, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Ga, Zr, Mo, Br, Nb, Ag, Pb, Ba, Sr, Pm, Y, Rb, Pd, Fr, U, In, As, Sn, Th, La, Cs, Sb, Po, Se, Si) at site 1 and 43 elements ( B, Na, Mg, Al, P, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Ga, Zr, Mo, Br, Nb, Ag, Pb, Ba, Sr, Pm, Y, Rb, F, Pd, Fr, U, In, As, Sn, Th, La, Pu, Os, Tl, Cd, Te, Si ) at site 2 were identified by WD-XRF in all the PM2.5 samples (Table S1). The mean levels of major and trace components in PM2.5 were measured at site 1 is 16.2 ± 2.2 µg m− 3 (14.9%) and at site 2 is 26.1 ± 5.1 µg m− 3 (16.9%). The Major elements in PM2.5 samples were assessed that include Cl, K, Fe, S, Si, Zn, Ca, and Al at site 1 and Si, K, Fe, S, Cl, Ca and Al at site 2 (Fig S1).
The seasonal statistics for each element for both the sites in relation to PM2.5 are summarized in Table S2 and Table S3, respectively, along with each element's specific contribution to PM2.5. Major components in PM2.5 samples were estimated for Cl, K, Fe, S, Si, Ca, and Al at both sites throughout all seasons. The summer months accounted for ~ 22% at site 1 and ~ 23% at site 2, making it the season with the largest percentage contribution to the total elemental composition of PM2.5 mass. The monsoon season contributed ~ 19% at site 1 and ~ 19% at site 2. The post-monsoon season contributed ~ 11% at site 1 and ~ 17% at site 2 to the overall elemental composition of PM2.5 mass, while the winter months provided ~ 12% at site 1 and ~ 11% at site 2.
Major elements that contributed to the concentration of PM2.5 during the winter season included Cl (4.58 ± 1.24 µg m− 3), Fe (2.82 ± 0.33 µg m− 3), K (2.74 ± 0.39 µg m− 3), S (2.72 ± 0.40 µg m− 3), Zn (1.37 ± 0.18 µg m− 3) and Si (0.95 ± 0.15 µg m− 3) at Site 1 and S (3.63 ± 0.42 µg m− 3), Fe (3.42 ± 0.33 µg m− 3), Si (3.37 ± 0.44 µg m− 3), K (3.40 ± 0.53 µg m− 3), Cl (2.65 ± 0.66 µg m− 3), Ca (1.96 ± 0.33 µg m− 3), Zn (1.38 ± 0.20 µg m− 3), and Al (1.35 ± 0.18 µg m− 3) at site 2, comprising 74% and 81% of the total elemental contribution at sampling locations, respectively. On the other hand, during the summer season, significant contributions from Cl (3.83 ± 0.76 µg m− 3), K (2.78 ± 0.32 µg m− 3), Fe (2.14 ± 0.24 µg m− 3), S (1.75 ± 0.15 µg m− 3), Si (1.34 ± 0.23 µg m− 3), Zn (0.99 ± 0.14 µg m− 3), La (0.89 ± 0.89 µg m− 3) and Pd (0.7546 ± 0.3793 µg m− 3) at Site 1 and Fe (2.82 ± 0.40 µg m− 3), Ag (2.76 ± 1.40 µg m− 3), Si (2.76 ± 0.31 µg m− 3), Pd (2.21 ± 1.45 µg m− 3), K (2.01 ± 0.37 µg m− 3), Ca (1.52 ± 0.18 µg m− 3), S (1.45 ± 0.18 µg m− 3), Cr (1.40 ± 0.38 µg m− 3) and Al (1.10 ± 0.12 µg m− 3) at site 2 having a combined elemental contribution to PM2.5 elemental concentrations of 77% and 81% respectively at both sites. In the monsoon season, notable contributors were Fe (1.69 ± 0.16 µg m− 3), K (1.36 ± 0.09 µg m− 3), S (1.31 ± 0.09 µg m− 3), Zn (0.69 ± 0.09 µg m− 3), Si (0.78 ± 0.07 µg m− 3), Ca (0.39 ± 0.03 µg m− 3) and Pd (0.34 ± 0.15 µg m− 3) at Site 1 and Si (2.96 ± 0.68 µg m− 3), Fe (2.08 ± 0.32 µg m− 3), Ca (1.62 ± 0.41 µg m− 3), Al (1.18 ± 0.27 µg m− 3), K (0.96 ± 0.19 µg m− 3), Pd (0.89 ± 0.34 µg m− 3), and S (0.86 ± 0.17 µg m− 3) at Site 2, contributing 71% and 64%, respectively, of the total elemental mass concentrations of PM2.5. During the post-monsoon season, Cl (5.27 ± 0.90 µg m− 3), K (3.97 ± 0.57 µg m− 3), S (3.25 ± 0.67 µg m− 3), Fe (2.67 ± 0.38 µg m− 3), Si (1.39 ± 0.23 µg m− 3), Zn (1.08 ± 0.15 µg m− 3), Ca (0.58 ± 0.04 µg m− 3) and Al (0.55 ± 3.09 µg m− 3) at Site 1 and Si (7.13 ± 1.98 µg m− 3), K (6.90 ± 1.90 µg m− 3), Cl (5.80 ± 1.09 µg m− 3), S (4.47 ± 0.70 µg m− 3), Fe (3.75 ± 0.42 µg m− 3), Al (2.85 ± 0.79 µg m− 3), Ca (2.82 ± 0.47 µg m− 3), Zn (1.18 ± 0.14 µg m− 3), and Pd (0.92 ± 0.39 µg m− 3) became significant contributors, making up 84% and 89% of the elements that contribute overall to PM2.5 concentrations.
The constant detection of Si, Ca, and Al in PM2.5 throughout all season points to a prominent contribution of the crustal dust to the PM2.5 mass loading (Gupta et al. 2024). Regional construction operations in the region, where concrete was being mixed in the vicinity of the site, are blamed for the accumulation of Ca (Gugamsetty et al. 2012). The constant monitoring of K throughout the year could be related to activities involving combustion and crustal dust (Jain et al. 2017; Sharma et al. 2022). Cl is present in PM2.5 samples, and combustion and biomass burning are the likely contributing sources (Jaiprakash et al. 2017; Chang et al. 2018; Lang et al. 2018). Due to the proximity of some metal manufacturing facilities to the sampling sites, the metal elements Fe and Zn are thought to have originated from both industrial and vehicular sources. (Gugamsetty et al. 2012; Sharma et al. 2014; Sharma and Mandal. 2023). During the sampling period, WD-XRF reliably detected 22 elements at site 1 and 21 elements at site 2 consistently in all PM2.5 samples, which was further utilized as input in the PMF (Table S5).
3.3 Source Apportionment
The PMF 5.0 version of positive matrix factorization was utilized to extract further source information for the components in PM2.5. For the 2022–2023 year, the most dependable five-factor solution was determined to use 22 species (B, Na, Mg, Al, P, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Ga, Zr, Mo, Br, Pb, Si) at site 1 (extra modelling uncertainty of 12%) and 21 elemental species (Na, Mg, Al, P, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Ga, Zr, Mo, Br, Pb, Si ) at site 2 (extra modelling uncertainty of 13%). Figure 3 (Tables S6 and S7) displays the source profiles and percentage contribution found by the PMF analysis. For the study period, PM2.5 was evaluated for five factors: fossil fuel combustion (FFC), biomass burning (BB), industrial emissions (IE), crustal dust (CD), and mixed sources at both the sampling sites.
3.3.1 Crustal Dust
The PMF analysis encompassed crustal dust, contributing 22% at both sites. Crustal dust with higher loadings for Mg (81%), Al (71%), Si (70%), Ca (64%), and Na (52%) at Site 1, while higher loadings for Al (71%), Si (71%), Ca (69%), Mg (52%) Ti (48%) and Fe (32%) at site 2. Mg, Al, Si, Ca, Na, and other elements are reported by a number of different studies as signs of a crustal dust source (Gugamsetty et al. 2012; Waked et al. 2014; Khan et al. 2016; Jeong et al. 2017; Manousakas et al. 2022; Cheong et al. 2024). The principal components of reconstituted dust, which are mostly from building operations, are Ca, Ti, Fe, Al, and Si (Song 2006; Cesari et al. 2018; Wang et al. 2024). An extensive collection of marker elements, including Al, Si, Ca, Ti, Fe, Pb, Cu, Cr, Ni, Co, and Mn, is used in India to identify soil dust (Gupta et al. 2012; Banerjee et al. 2015; Sharma et al. 2016b; Jain et al. 2017). The other studies on source apportionment have demonstrated the higher relative contributions of Ca in road dust; generally, construction activities and mineral dust are linked to Ca and Mg (Bukowiecki et al. 2010; Crilley et al. 2016; Maenhaut. 2017; Rai et al. 2020a b). Because of the influence of heavy traffic, the sampling site's closeness to the motorway shows that it is susceptible to the deterioration of both asphalt and concrete roads. The substantial usage of concrete and asphalt in road building may be the cause of the elevated concentration of crustal elements like Ca and Mg in road dust (Fullova et al. 2017; Gupta et al. 2024).
3.3.2 Fossil Fuel Combustion
Fossil fuel combustion, contributing 18% at site 1 and 17% at site 2 to the PM2.5 mass having higher loadings of Mo (100%), S (32%), B (30%), K (25%) and Ca (22%) at site 1 and Cl (72%), S (64%), K (58%), Zn (39%) and Mn (18%) at Site 2. Due to the presence of industries that consume a lot of fossil fuels for energy and manufacturing processes, site 1 emits more emissions in comparison to site 2. Coal combustion is represented by high Cl load to PM (Zheng et al. 2005; Song 2006). The source of PM2.5 combustion from burning fossil fuels is indicated by the amounts of Zn and Cl at the sampling locations. (Sharma et al. 2014; 2016a; 2016b). B and Mo are attributed to coal burned during combustion (Senior et al., 2020). Zn are typical coal combustion marker species (Lee et al. 2002). K+ and Cl− are also attributed to coal combustion sources (Lang et al. 2018). The contribution of K, Cl, and S to combustion was also reported in several studies (Singhai et al. 2017; Chang et al. 2018; Sharma et al. 2022; Sharma and Mandal. 2023). The burning method, product toxicity, fuel shape, fire plot orientation, temperature, oxygen concentration, and material composition all affect combustion effluents. The composition of these materials varies depending on the conditions under which they burn and their organic and elemental makeup (Chanana et al. 2023).
3.3.3 Biomass burning
The PMF analysis reveals the biomass burning factor that contributed 19% at site 1 and 20% at site 2 for PM2.5 mass composition having higher loadings for Cl (88%), K (47%), B (41%), S (35%), Zn (29%), P (26%) and Fe (24%) at Site 1 and P (75%), Ni (42%), S (31%), K (29%), Ti (24%) and Fe (24%) at Site 2. In comparison to site 1, site 2 (the residential site) has a larger population density, which encourages the more frequent and extensive use of biomass for heating and cooking. As a result, local pollutant concentrations are higher there. Biomass burning is characterized by high K (Song 2006). The farmers burn the leftover crop material every summer and post-monsoon season for the preparation of the fields for the next crop. An additional factor in the quantity of biomass burned in the post-monsoon season is the burning of leaves that have fallen throughout the city. The literature has frequently referenced K as a major tracer for a biomass or wood-burning source (Song 2006; Ram et al. 2010; Dall’Osto et al. 2013; Kim and Hopke 2007; Mustaffa et al. 2014; Wahid et al. 2013; Sun et al. 2021; Chansuebsri et al. 2024; Wang et al. 2024). According to Khan et al. (2016), the biomass burning source often consists of wild forest fires, agricultural waste and/or residue from burning wood used for residential purposes. Previous studies has shown that burning agricultural residue outdoors releases emissions of Na and Cl (Singhai et al. 2017). Burning biomass can release phosphorus into the atmosphere since P is related to the creation or use of fertilisers (Shankar et al. 2023). Plant materials contain phosphorus; when burned, they can be emitted as PM (Akagi et al. 2011; Bhuvaneshwari et al. 2019; Meng et al. 2022). High K and S concentrations have been reported in biomass burns, wood burning, and vegetative burning. (Gugamsetty et al. 2012).
3.3.4 Industrial emissions
Industrial factor attributed to 22% at Site 1 and 27% at Site 2. The higher loading of elements such as Br (94%), Ti (67%), Ni (43%), Cr (42%), Na (30%), Mn (29%), S (27%), Zr (26%), Pb (26%) and Fe (20%) at Site 1 and Ga (74%), Mo (73%), Zr (63%), Cr (56%), Cu (55%), Pb (52%), Br (44%), Mn (35%), Zn (35%) and Fe (23%) at site 2 are attributed to industrial sources. Site 2 has a higher concentration than Site 1 due to the dispersal of pollutants by wind and the absence of efficient pollution control measures at the source or during transit. An additional factor is that site 2 can include several sources of pollution, such as household activities and transportation, which might exacerbate the effects of industrial emissions. Zn, Cu, and Pb are closely associated with metal processing and industrial production (Wang et al. 2024). Mn, Mo, Fe, Cr, S, Ni, Cu, Zn, and Pb were classified as the industry sources (Gugamsetty et al. 2012; Sharma et al. 2014; Banerjee et al. 2015; Jain et al. 2017; Lang et al. 2018; Sharma and Mandal. 2023; Cheong at al. 2024) as many industries like metal manufacturing plants, iron and steel industry, electronics, dyeing, paint, rubber mill, textile, leather and automobile product industries are located near the sampling sites. In terms of fine particles, the textile industry primarily uses Br and Zn; steelworks are linked to Mn and Fe; and industrial activities like metal smelting are linked to Ni, Cu, Zn, and Pb. (Lang et al. 2018). Ti is released as TiO2, which is utilized in ore mining operations and serves as a tracer for emissions linked to dust (Gupta et al. 2024). According to Fang et al. 2019, Ga is produced through industrial processes like metal processing and semiconductor manufacture. GaO₃, which can exist in the form of small particulate particles, is created when Ga reacts with oxygen in the air.
3.3.5 Mixed Sources (Site 1: VE + IE + CD and Site 2: VE + CD)
The source of PM2.5 is extracted as a mixed source with Ga (100%), Cu (73%), Zr (54%), Zn (37%), Mn (36%), Fe (29%), Ni (23%) and Pb (22%) at Site 1 and Na (100%), Mg (38%), Ni (26%) and Cu (20%) rich profile at site 2 contributing overall 19% and 14% of total PM2.5 mass loadings, respectively at both the sampling sites. Pollutant contribution at Site 1 are higher than at Site 2 due to the dense concentration of different machinery and activities that release pollutants. Exhaust from motor vehicles is typified by heavy Pb and Zn. Tyres, brake linings, additives in motor oil and lubricating oil all release Zn emissions (Zhou et al. 2004; Song 2006; Cheong et al. 2024). Ni is frequently utilised as a traffic source tracer since it is a crucial part of three-way catalytic converters (Lang et al. 2018). Tyres and brake wear are linked to Cu, Pb, Ni, Zn, Fe, and other elements (Gugamsetty et al. 2012; Cesari et al. 2018; Shankar et al. 2023; Cheong et al. 2024). While Ga and Cu originate from the metal processing and manufacturing industries, Na and Mg elements are the primary components of airborne soil and road dust and typically contribute significantly to coarse aerosol (Lang et al. 2018; Fang et al. 2019; Gugamsetty et al. 2012; Sharma and Mandal. 2023). Cu and Ga are released by the electroplating, metal finishing, and electronics manufacturing industries present near site 1. Moreover, the region's emissions may potentially be influenced by the recycling and metal processing processes. Mg, Fe, and Mn, originate from crustal elements (Cheong et al. 2024).