Effect of organic carbon on light absorptivity of biodiesel combustion particulate matter

Abstract The carbonaceous composition of particulate matter (PM) directly influences its light‐absorbing properties. To study the light absorption characteristics of PM emitted from biodiesel combustion, PM samples were collected from engines fueled with diesel, palm oil methyl ester (PME), waste cooking oil methyl ester (WME), and soybean oil methyl ester (SME). By integrating ultraviolet–visible spectrophotometry with carbonaceous component analysis, the mechanism through which organic carbon (OC) components influence the light absorption behavior of biodiesel‐derived PM was investigated. Results show that PM from diesel combustion exhibits significantly higher light absorption intensity than that from biodiesel combustion, with the light absorption capacity of biodiesel‐derived particles increasing as fuel iodine value rises. OC2 dominates OC in diesel‐derived particles, whereas OC in biodiesel‐derived particles is composed of OC2, OC3, and OC4, among which OC3 has the highest proportion. Furthermore, the mass absorption cross‐section (MAC) of elemental carbon (EC) is greater in biodiesel combustion particles than in diesel combustion particles, and the magnitude of light absorption enhancement correlates positively with increasing OC/EC ratios. These findings highlight the critical role of brown carbon in enhancing light absorption in biodiesel‐generated particulate matter.