Regional Differences in the Light Absorption Properties of Fine Particulate Matter Over the Tibetan Plateau: Insights From HR‐ToF‐AMS and Aethalometer Measurements

Abstract

The Tibetan Plateau (TP) has received wide scientific concern in recent decades owing to its important impacts on regional climatic and cryospheric changes, hydrological cycles, and environments. However, our understanding of the spatial distribution of the chemical and optical properties of aerosols is still limited based on prior single‐site observations. In this study, aerosol light absorptions from black carbon (BC) and brown carbon (BrC) were explored and compared among three remote TP sites, including Qomolangma Station (QOMS) on the southern TP, Nam Co Station (NamCo) on the central TP, and Waliguan Observatory on the northeastern TP. Although the aerosol mass concentration at QOMS was less than half of that at Waliguan, the light absorption coefficient of aerosols at QOMS was nearly 5 times higher than that at Waliguan, mainly as a result of more light‐absorbing carbonaceous aerosols on the southern TP due to long‐range transported biomass burning emissions. Specifically, BC dominated aerosol light absorption at all wavelengths, whereas BrC contributed ∼30% of the light absorption at 370 nm at QOMS and ∼20% at Waliguan and NamCo. A major contributor to BrC light absorption at QOMS was biomass burning‐related organic aerosols apportioned from aerosol mass spectrometry measurements. Understanding the significant regional differences in aerosol light absorption properties on the TP is useful for evaluating the regional climatic and environmental effects and validating the model results on aerosol radiative forcing.

Characterization of Aerosol Properties from the Burning Emissions of Typical Residential Fuels on the Tibetan Plateau

“…The fb abs,BrC was calculated according to the traditional AAE attribution method by assuming its negligible contribution at 880 nm and the AAE of pure BC particles (AAE BC ) to be unity, expressed as fb abs,BrC,λ = 1–( b abs,880 / b abs,λ ) × (λ/880) −AAE BC ). Detailed information about the calculations of the above optical parameters can be referred to our previous publication …”

“…Detailed information about the calculations of the above optical parameters can be referred to our previous publication. 55 Clearly, a negative correlation between f OA and MCE whereas a positive correlation between f BC and MCE were found among the nine burning emissions (Figure 3), with Pearson's correlation coefficients (Pr) of −0.66 and 0.68, respectively. As a result, the OA/BC ratio, which was an important diagnostic index for indicating the combustion conditions or parametrizing the OA effective absorptivity, 56 showed a tightly negative correlation with MCE (Pr = −0.78).…”

High-resolution physicochemical dataset of atmospheric aerosols over the Tibetan Plateau and its surroundings

“…Comparatively, the Babs at 370 nm at QOMS was five times as high as that at Waliguan although its relatively low PM1 mass was observed, mainly as a result of the higher contribution of light-absorbing aerosol components in the southern TP regions (e.g., OA and BC together contributed nearly 80% of the total PM1 at QOMS whereas this contribution decreased to only 37.5% at Waliguan). The obviously higher AAE at QOMS also suggested the dominant lightabsorbing contribution of BrC or important lensing effect of non-BC materials coated on BC cores at this site (Zhang et al, 2021). As shown in the inserted plots in Fig.…”

“…The contribution of BrC to total Babs (fBabs,BrC) at a short wavelength λ is calculated as fB abs,BrC,λ = 1 − (B abs,880 /B abs,λ ) × (λ/880) −AAE BC by assuming its negligible contribution at 880 nm. Detailed information about the data correction and calculation of this instrument can be found in our previous publication (Zhang et al, 2021). The CCN-100 supersaturates the sampled aerosol particles in a 50-cm-high column with continuously wetted walls and a longitudinal thermal gradient, so that those particles grow into detectable CCN particles and are measured using an optical ) of these sites were different, the significantly distinct PM1 mass and chemical compositions could basically reflect the regional difference of aerosol mass levels, properties, and sources at different regions.…”

A New Method for Eliminating Dust Effects When Quantifying the Light Absorption Properties of Brown Carbon

“…This algorithm proposed by Qin et al. (2018) has now been widely used worldwide because of its advantages in separating the absorption coefficients of individual BrC components (Cappa et al., 2019; de Sá et al., 2019; Kaskaoutis et al., 2021; Kasthuriarachchi et al., 2020; Singh et al., 2021; Q. Y. Wang et al., 2019; J. F. Wang et al., 2021; Y. J. Zhang et al., 2020; X. H. Zhang et al., 2021). The studies applying this algorithm (Figure 1 and Text S1 in Supporting Information ) reveal that biomass combustion‐related OA and secondary OA (SOA) are the most significant contributors to NBC absorption at 370 nm worldwide.…”