Source Identification of PM2.5 during a Smoke Haze Period in Chiang Mai, Thailand, Using Stable Carbon and Nitrogen Isotopes

Abstract

Open biomass burning (BB) has contributed severely to the ambient levels of particulate matter of less than 2.5 μm diameter (PM2.5) in upper northern Thailand over the last decade. Some methods have been reported to identify the sources of burning using chemical compositions, i.e., ions, metals, polycyclic aromatic hydrocarbons, etc. However, recent advances in nuclear techniques have been limited in use due to their specific instrumentation. The aims of this study were to investigate the sources of ambient PM2.5 in Chiang Mai city using stable carbon (δ13C) and nitrogen isotopes (δ15N). The mean concentrations of total carbon (TC) and total nitrogen (TN) in PM2.5 were 12.2 ± 5.42 and 1.91 ± 1.07 μg/m3, respectively, whereas δ13C and δ15N PM2.5 were −26.1 ± 0.77‰ and 10.3 ± 2.86‰, respectively. This isotopic analysis confirmed that biomass burning was the source of PM2.5 and that C3 and C4 plants contributed about 74% and 26%, respectively. These study results confirm that the stable isotope is an important tool in identifying the sources of aerosols.

Comprehensive review of the annual haze episode in Northern Thailand

“…C3 plants range from -37 to -20 ‰ and mixed deciduous forest in northern Thailand have values between -27.9±0.7 and -29.6±0.6 ‰., covering the range of values found in particulate matter (Fig 4.9). Song et al, 2022) This paper is a non-peer reviewed draft -currently not submitted to any journal Nitrogen isotopes have also been considered to help further source distinction and show a slow increase of δ 15 N from 7.76±1.32 to 12.7±1.61 ‰ during the burning season (Kawichai et al, 2022). 15 N/ 14 N values are coherent with 14 C data and exclude a large fossil fuel component in particulate matter.…”

“…Particulate matter shows δ 13 C between -25.3±0.46 and -27.9±0.67 ‰ slowly increasing through the haze season (Kawichai et al, 2020b(Kawichai et al, , 2022 which is considerably different from C4 plants (-16 to -11 ‰) including corn (-11.6 to -16.1 ‰) and sugarcane (-12.1 to -12.9 ‰). C3 plants range from -37 to -20 ‰ and mixed deciduous forest in northern Thailand have values between -27.9±0.7 and -29.6±0.6 ‰., covering the range of values found in particulate matter (Fig 4.9).…”

“…Carbon is the major component of particulate matter. It forms 50-60 wt.% (Pani et al, 2019;Kawichai et al, 2022;Suriyawong et al, 2023). It is divided into two fractions called elemental carbon and organic carbon based on their composition and various analytical properties.…”

“…This form of carbon is combined with other elements in order to form complex organic molecules. These elements are mostly nitrogen (5-10 wt.%) (Kawichai et al, 2022), oxygen and hydrogen.…”

“…32 Figure 4.9. Discriminative plot of the haze carbon and nitrogen isotopic signature (red dots) and trend through time (purple arrow) compared to unspecific sources (motor vehicles, C3-& C4-plants) and potential specific sources (local deciduous forests, corn, soy, rice, sugarcane) (modified from Kawichai et al, 2020bKawichai et al, , 2022 with additional data from Spain & Le Feuvre, 1996;Turekian et al, 1998;Yoneyama et al, 2001;Marinaeli et al, 2002;Krull et al, 2003;Kell et al, 2005;Widory, 2007;Jahren & Kraft, 2008;Das et al, 2010;Pavuluri et al, 2010;Kaushal & Ghosh, 2018;Ma et al, 2021;Kato et al, 2023. This paper is a non-peer reviewed draft -currently not submitted to any journal Sulfate anthropogenic source component makes it less variable than other components and is preponderant outside the haze episode (Sopajaree et al, 2011;Tsai et al, 2013;Khamkaew et al, 2017;Janta et al, 2020;Chansuesubsri et al, 2021a,). However, sulfate production is also found in biomass burning (Sillapapiromsuk et al, 2013) but the negative correlation with increasing particulate matter concentration indicates that biomass is possibly not the dominant source (Chansuebsri et al, 2022).…”