Abstract
Aerosol mixing state is one of the most important factors determining the impacts of aerosol particles on aerosol-cloud-climate interactions and human health. The size, composition, and morphology of about 32,000 single particles are analyzed using transmission electron microscopy (TEM) to evaluate per-particle mixing state. Based on the TEM analysis, we quantify aerosol mixing state and examine the impacts of per-particle mixing state on cloud condensation nuclei (CCN) properties and particle deposition efficiency along the human respiratory tract. Assuming homogeneous chemical composition across the aerosol population, a common practice in many global and regional models to various extents, we show that such simplification of mixing state representation could potentially lead to remarkable errors, a maximum of about 90% and 35%, in CCN concentrations and deposition efficiency calculations respectively. Our results from ambient per-particle observations highlight the importance of considering aerosol mixing state in both air quality models and climate models.
Highlights
Aerosol particles play multiple important roles in the atmosphere
This study aims to (i) present physicochemical properties of single particles analyzed by transmission electron microscopy (TEM); (ii) characterize aerosol mixing state by applying mixing state index; and (iii) examine the impact of mixing state on climate-relevant cloud condensation nuclei (CCN) properties and particles deposition efficiencies in the human respiratory tract
By quantifying the aerosol mixing state in term of χ, this study connects TEM single particle analysis of the ambient samples collected from urban, mountain, and rural sites to the study of aerosol impacts on climate and human health
Summary
Aerosol particles play multiple important roles in the atmosphere. From the climate aspect, they can act as cloud condensation nuclei (CCN) and ice nuclei (IN) and scatter and absorb solar and terrestrial radiation, resulting in changing the Earth energy budget directly and indirectly.[1,2,3,4,5] From the human health aspect, particulate matters from local emission, regional scale and longrange transport deteriorate air quality[6,7] and are blamed for increasing incidence of cardiovascular diseases and mortality rate.[8,9,10] These impacts depend on the aerosol physicochemical properties, which require detailed studies (i) to reduce the uncertainty in aerosol-cloud-climate interactions, one of the largest uncertainties in climate projection;[5,11] and (ii) to understand the various aerosol impacts on human health.[12,13,14] Numerous studies of laboratory experiments, field observations, and model simulations have examined aerosols to understand their fundamental properties, atmospheric transformation and impacts on climate and human health.In recent decades, representations of aerosol physicochemical properties in regional and global models have been improved.[15,16,17,18,19,20,21,22,23] due to computational constraint, these model representations have been unavoidably simplified to certain degrees and may lead to erroneous calculations of climaterelevant quantities to various extents. More explicit representations of aerosol physicochemical properties and simulations of aerosol atmospheric processing have been conducted in process level modeling frameworks[24,25,26,27,28,29,30] to evaluate the impacts of aerosols on climate-relevant quantities. Curtis et al.,[31] developed particle-resolved aerosol representation in single column mode of WRF-Chem meteorology-chemistry coupled model to simulate vertical distribution of mixing state. Ching and Kajino[14] evaluated the mixing state impact on particle deposition efficiency in the human respiratory tract by developing particle-resolved deposition model
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