Abstract
Abstract. Number concentrations, size distributions, and mixing states of aerosols are essential parameters for accurate estimations of aerosol direct and indirect effects. In this study, we develop an aerosol module, designated the Aerosol Two-dimensional bin module for foRmation and Aging Simulation (ATRAS), that can explicitly represent these parameters by considering new particle formation (NPF), black carbon (BC) aging, and secondary organic aerosol (SOA) processes. A two-dimensional bin representation is used for particles with dry diameters from 40 nm to 10 μm to resolve both aerosol sizes (12 bins) and BC mixing states (10 bins) for a total of 120 bins. The particles with diameters between 1 and 40 nm are resolved using additional eight size bins to calculate NPF. The ATRAS module is implemented in the WRF-Chem model and applied to examine the sensitivity of simulated mass, number, size distributions, and optical and radiative parameters of aerosols to NPF, BC aging, and SOA processes over East Asia during the spring of 2009. The BC absorption enhancement by coating materials is about 50% over East Asia during the spring, and the contribution of SOA processes to the absorption enhancement is estimated to be 10–20% over northern East Asia and 20–35% over southern East Asia. A clear north–south contrast is also found between the impacts of NPF and SOA processes on cloud condensation nuclei (CCN) concentrations: NPF increases CCN concentrations at higher supersaturations (smaller particles) over northern East Asia, whereas SOA increases CCN concentrations at lower supersaturations (larger particles) over southern East Asia. The application of ATRAS in East Asia also shows that the impact of each process on each optical and radiative parameter depends strongly on the process and the parameter in question. The module can be used in the future as a benchmark model to evaluate the accuracy of simpler aerosol models and examine interactions between NPF, BC aging, and SOA processes under different meteorological conditions and emissions.
Highlights
Atmospheric aerosols play an important role in Earth’s climate system by scattering and absorbing solar radiation and by modifying the microphysical properties of clouds and precipitation
The vertical profiles of cloud condensation nuclei (CCN) and mass concentrations show that the features obtained at an altitude of about 1 km are seen at all levels (Fig. 7): Organic aerosol (OA) and CCN0.1 concentrations are higher in the simulations with the OA formation scheme, black carbon (BC) mass concentrations are higher in the simulations that resolve mixing states, and CCN1.0 concentrations are higher in the simulations with new particle formation (NPF)
We focus on column aerosol optical depth (AOD), column absorption AOD (AAOD), singlescattering albedo (SSA) at 1 km, heating rate by aerosols at (a)
Summary
Atmospheric aerosols play an important role in Earth’s climate system by scattering and absorbing solar radiation (direct effects) and by modifying the microphysical properties of clouds and precipitation (indirect effects). We developed modules for NPF, BC aging, and secondary OA (SOA) processes individually using the Weather Research and Forecasting and Chemistry (WRF-Chem) model (Matsui et al, 2011, 2013a, b, 2014) These modules succeeded in explaining important aerosol properties related to number concentrations, size distributions, and mixing states of aerosols in the atmosphere. Our BC mixing-state-resolved aerosol module (Matsui et al, 2013a) calculates BC aging processes using a two-dimensional aerosol bin representation (12 × 10 bins) that resolves both aerosol sizes (from 40 nm to 10 μm in diameter) and BC mixing states (pure-BC particles, BC-free particles, and eight different internally mixed BC particles) This module reproduced the features of the BC mixing state observed by a single-particle soot photometer (SP2) during the Aerosol Radiative Forcing in East Asia (AFORCE) aircraft campaign, and it was used to evaluate the impact of the treatment of BC mixing state on radiative and microphysical properties of BC over the East Asian region. We describe the ATRAS module (Sect. 2) and present the first results of its application over East Asia to examine the sensitivity of mass, number, size distributions, and optical and radiative parameters of aerosols to NPF, BC aging, and SOA processes (Sect. 3)
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