## 1 Introduction
Both environmental and occupational exposures to inorganic arsenic have been related to an increased cardiovascular mortality [20], and clinical studies demonstrated arsenic induced hypertension atherosclerosis, stroke, coronary heart disease, and diabetes mellitus in a dose-dependent manner [21]. Additionally, the occupational exposure limit for lead in air set out in the Regulations is 0.15 ug/m\({}^{3}\), and a concentration above that level may have been shown to affect blood which may lead to anemia, and affect the nervous system and kidney, as well as infertility in males [22]. Cadmium, being carcinogenic in humans, had an exposure limit measured over a 15 min period and has been set at 0.05 mg/m\({}^{3}\) of air [23]. In addition, the exposure to elements such as, Cd, Hg, and Pb is statistically associated with cardiovascular diseases [21]. Nickel exposure limit was set at 0.5 mg/m\({}^{3}\) averaged over an 8 h period [24] and its exposure above the accepted level has shown significant effect on heart rate variability [25], and increased concentrations of nickel, zinc, and lead have been reported to be associated with an increase in emergency department (ED) visits for cerebral hemorrhage in China [26]. Several published papers have suggested that PM2.5 is associated with cardiovascular or respiratory diseases, and dementia [27]; still level or component of indoor PM2.5 components affecting health remains insufficient. Due to such vital importance of PM2.5 components, recently, studies on heavy metals in PM2.5 have been actively conducted to identify their sources. Inductively Coupled Plasma (ICP) Spectrometer and X-Ray Fluorescence Spectrometer (XRF) have been used to analyze the heavy metals [28; 29; 30]. Although ICP has a lower detection limit which ranges from <1 ppm to >100 ppm [31], and XRF detection limits for most elements are 2-20 ng/cm\({}^{2}\) for micro sample surface, thin samples, aerosols, and liquids [32], both XRF and ICP devices have comparable element detection capacities for ambient samples, with lower measurement error. Both techniques are capable of giving excellent accuracy and precision [33]. However, ICP requires relatively sophisticated pre-sample treatment techniques using ferric acid with hydrochloric acid [34], and ICP is often a destructive analytical procedure, meaning that the sample cannot be recovered after analysis, whereas XRF is a completely non-destructive method of testing that provides accurate materials analysis, and the same sample can be used for other analyses with a short sample preparation time, thus more advantageous in the analysis [35]. According to [PERSON] et al. [36], in a two-week study that assessed the effect of heavy metals in PM2.5 on human health using ICP-MS and XRF, Fe, Mn, Zn, Pb, and Cu, these were found to show correlation coefficients of 0.7 or more. For 24 h filter samples studied with Inductively Coupled Plasma Mass Spectrometry (ICP-MS), the detection limit was low; therefore, the number of elements that passed the quality criteria was high. By default, direct comparison of the two different techniques, ICP-MS, and Energy Dispersive X-ray Fluorescence (ED-XRF), showed good correlation for both 24-hour and 2-week filter samples [36]. Results of previous studies had shown that ICP is beneficial for the precise analysis of low-concentration samples as low as 1.3 ng/m\({}^{3}\)[36], although the sample preparation process was relatively longer. XRF data, on the other hand, can be analyzed in various ways without sample preparation, suggesting the analysis to be relatively faster and reproducible. XRF can sufficiently measure heavy metals in the atmosphere with samples collected at a low flow rate (0.5 L/min). Most heavy metals can be analyzed as long as the PM mass in the filter is above a certain level because low sample mass affect the reliability of metal analysis for both XRF and ICP-MS, therefore the 0.06 mg minimum cut-off for particle mass ensures reliable analysis results for most elements using ICP-MS [37].