Jianzhong Xu

and 8 more

Tibetan Plateau (TP) has aroused widely scientific concerns in recent decades owning to its important effects on regional climatic and cryospheric changes, hydrological cycle, and environments. However, our understandings on the chemical and optical properties of aerosols are still limited at those regions. In this study, regional difference of aerosol light absorption properties were explored at three remote TP sites, including Qomolangma Station (QOMS) in the southern TP, Nam Co Station (NamCo) in the central TP, and Waliguan Observatory in the northeastern TP. Although aerosol mass concentration at QOMS was less than half of that at Waliguan, the light absorption coefficient at QOMS was nearly 5 time higher than that at Waliguan, mainly as a result of the high contributions of light-absorbing carbonaceous aerosols in the southern TP from the long-range transported biomass burning emissions of South Asia. An improved method was used to derive the near-realistic absorption Ångström exponent for pure black carbon (BC) particles. BC dominated the light absorption at all wavelengths, whereas brown carbon (BrC) contributed more than 30% of the light absorption at 370 nm at QOMS and ~ 20% at Waliguan and NamCo. The major contributor to BrC light absorption at QOMS was the biomass burning related organic aerosol. Radiative transfer simulations also showed the highest atmospheric radiative forcings at QOMS among the three campaigns. The significant regional differences of aerosol light absorption properties in the TP might be related tightly with the different aerosol sources and chemical processes.

Huan Yu

and 8 more

We investigated size-dependent molecular characteristics of coastal organic aerosols from < 0.032 μm to 3.2 μm at a new particle formation (NPF) hotspot of east China by using Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR-MS). Strong connection between C20-33HhOo/C18,30HhOoNn compounds in particles smaller than 0.10 μm and the VOCs emitted from local intertidal macroalgae suggests that the organic compounds (OC) in ultrafine particles are formed probably via the gas-phase oxidation of long-chain fatty aldehydes or acids, followed by particle-phase accretion reactions or imine formation during the coastal NPF events. In 0.18-0.56 μm particles, dominant C8-C20 CHO, CHON, CHOS and CHONS compounds (maximum: C10 or C15) are suggested most likely to be terpene oxidation products. Highly oxygenated compounds with 0.6 ≤ H/C ≤ 1.5 and 0.67 ≤ O/C ≤ 1.2 reside mostly in 0.18-0.56 μm particles, accounting for 5% of the OC formulas in this size range. Iodinated OC are subsequently formed via electrophilic substitution of non-iodinated OC by iodine cations in iodine-rich particles. CHN and Cl/Br-containing OC account altogether for only 1-4% of total OC intensity. As a result of the above compound distribution, the intensity weighted unsaturation degree and carbon oxidation state of OC increase with particle size. The distribution of aromatic compounds (i.e. Aromaticity Index > 0.5) is bimodal with peaks in 0.056-0.18 μm and 1.0-3.2 μm. In addition, our study observed higher unsaturation degree, carbon oxidation state and aromaticity of OC in coastal PM2.5 than inland urban PM2.5 in the same region.