In this study, we show that black carbon (BC) mass concentrations measured by different techniques are consistent and traceable. First, we present the volatilities of 13 organic compounds passed through a heated inlet. These data were used to quantify the interference of organic aerosols on the BC measurement techniques. The masses of the refractory particles that incandesce (m*_ref) were used to calibrate BC mass measured by a single-particle soot photometer (SP2), which uses laser-induced incandescence. This calibration was influenced little by refractory organics and agreed well with that of fullerene soot, which indicates the consistency of the standards. We estimated the interference of pyrolyzed refractory organics on the BC measured with a filter-based absorption photometer continuous soot monitoring system (COSMOS) with a heated inlet to be small in Asia. This was also confirmed by the stable mass absorption cross section (MAC) obtained by the high correlations between BC mass concentrations measured by COSMOS (M _COSMOS) and those measured by the thermal-optical transmittance method (M _TOT) ( Kondo et al. 2009 Kondo, Y. , Sahu, L. , Kuwata, M. , Miyazaki, Y. , Takegawa, N. , Moteki, N. , Imaru, J. , Han, S. , Nakayama, T. , Hu, M. , Kim, Y. J. and Kita, K. 2009. Stabilization of the Mass Absorption Cross Section of Black Carbon for Filter-Based Absorption Photometry by the Use of a Heated Inlet. Aerosol Sci. Technol., 43: 741–756. [Taylor & Francis Online], [Web of Science ®] [Google Scholar] ). M _COSMOS was also compared with total BC mass concentrations measured with an SP2 (M _SP2) in Tokyo in 2009. M _COSMOS and M _SP2 were highly correlated (r ²= 0.97) and agreed to within about 10% on average. These results demonstrate that M _SP2, M _COSMOS, and M _TOT were nearly identical. Use of the masses of incandescing refractory BC particles for calibration of BC mass concentrations determined by different techniques gave consistent results.

The health implications of PM_2.5 in the tropical region of Southeast Asia (SEA) are significant as PM_2.5 can pose serious health concerns. PM_2.5 concentration and sources here are strongly influenced by changes in the monsoon regime from the south-west quadrant to the north-east quadrant in the region. In this work, PM_2.5 samples were collected at a semi-urban area using a high-volume air sampler at different seasons on 24 h basis. Analysis of trace elements and water-soluble ions was performed using inductively coupled plasma mass spectroscopy (ICP-MS) and ion chromatography (IC), respectively. Apportionment analysis of PM_2.5 was carried out using the United States Environmental Protection Agency (US EPA) positive matrix factorization (PMF) 5.0 and a mass closure model. We quantitatively characterized the health risks posed to human populations through the inhalation of selected heavy metals in PM_2.5. 48 % of the samples collected exceeded the World Health Organization (WHO) 24 h PM_2.5 guideline but only 19 % of the samples exceeded 24 h US EPA National Ambient Air Quality Standard (NAAQS). The PM_2.5 concentration was slightly higher during the north-east monsoon compared to south-west monsoon. The main trace metals identified were As, Pb, Cd, Ni, Mn, V, and Cr while the main ions were SO₄²⁻, NO₃⁻, NH₄⁺, and Na. The mass closure model identified four major sources of PM_2.5 that account for 55 % of total mass balance. The four sources are mineral matter (MIN) (35 %), secondary inorganic aerosol (SIA) (11 %), sea salt (SS) (7 %), and trace elements (TE) (2 %). PMF 5.0 elucidated five potential sources: motor vehicle emissions coupled with biomass burning (31 %) were the most dominant, followed by marine/sulfate aerosol (20 %), coal burning (19 %), nitrate aerosol (17 %), and mineral/road dust (13 %). The hazard quotient (HQ) for four selected metals (Pb, As, Cd, and Ni) in PM_2.5 mass was highest in PM_2.5 mass from the coal burning source and least in PM_2.5 mass originating from the mineral/road dust source. The main carcinogenic heavy metal of concern to health at the current location was As; the other heavy metals (Ni, Pb, and Cd) did not pose a significant cancer risk in PM_2.5 mass concentration. Overall, the associated lifetime cancer risk posed by the exposure of hazardous metals in PM_2.5 is 3–4 per 1 000 000 people at this location.