Humic-like substances (HULIS) in springtime aerosols at a high-altitude background station in the western North Pacific: Source attribution, abundance, and light-absorption

• Published in: The Science of the total environment Vol. 809; p. 151180
• Main Authors: Pani, Shantanu Kumar, Lee, Chung-Te, Griffith, Stephen M., Lin, Neng-Huei
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 25.02.2022
• Subjects: 7-SEAS/BASELInE; absorption; aerosols; Aerosols - analysis; Air Pollutants - analysis; Altitude; Biomass; Biomass-burning; carbon; Carbon - analysis; Environmental Monitoring; Humic Substances - analysis; Long-range transport; Lulin Atmospheric Background Station; Particulate Matter - analysis; Peninsular Southeast Asia; photochemistry; radiative transfer; refractive index; sea level; Simple forcing efficiency; source attribution; spring; troposphere; Simple forcing efficiency; 7-SEAS/BASELInE; Biomass-burning; Peninsular Southeast Asia; Long-range transport; Lulin Atmospheric Background Station
• ISSN: 0048-9697; 1879-1026; 1879-1026
• DOI: 10.1016/j.scitotenv.2021.151180

Atmospheric humic-like substances (HULIS) are important components of biomass-burning (BB) emissions and highly associated with light-absorbing organic aerosols (often referred to as brown carbon). This study highlights the importance of BB-emitted HULIS aerosols in peninsular Southeast Asian outflow to the subtropical western North Pacific. We determined various key light-absorbing characteristics of HULIS i.e. mass absorption cross-section (MACHULIS), absorbing component of the refractive index (kHULIS), and absorption Ångström exponent (AAEHULIS) based on ground-based aerosol light absorption measurements along with HULIS concentrations in springtime aerosols at Lulin Atmospheric Background Station (LABS; 2862 m above mean sea level), which is a representative high-altitude remote site in the western North Pacific. Daily variations of HULIS (0.58–12.92 μg m−3) at LABS were mostly linked with the influence from incoming air-masses, while correlations with BB tracers and secondary aerosols indicated the attribution of primary and secondary sources. Stronger light absorption capability of HULIS was clearly evident from MACHULIS and kHULIS values at 370 nm, which were about ~1.5 times higher during BB-dominated days (1.16 ± 0.75 m2 g−1 and 0.05 ± 0.03, respectively) than that during non-BB days (0.77 ± 0.89 m2 g−1 and 0.03 ± 0.04, respectively). Estimates from a simple radiative transfer model showed that HULIS absorption can add as much as 15.13 W g−1 to atmospheric warming, and ~46% more during BB-dominated than non-BB period, highlighting that HULIS light absorption may significantly affect the Earth–atmosphere system and tropospheric photochemistry over the western North Pacific. [Display omitted] •HULIS at Mt. Lulin was mostly attributed to both primary and secondary sources.•Biomass-burning was the dominating factor of HULIS abundance.•MACHULIS was 1.16 ± 0.75 m2 g−1 at 370 nm during biomass-burning dominated period.•HULIS can add up to 15.13 W g−1 to atmospheric warming over western North Pacific.