Articles | Volume 7, issue 6
Geosci. Model Dev., 7, 3153–3172, 2014

Special issue: The Modular Earth Submodel System (MESSy) (ACP/GMD inter-journal...

Geosci. Model Dev., 7, 3153–3172, 2014

Model description paper 21 Dec 2014

Model description paper | 21 Dec 2014

ORACLE (v1.0): module to simulate the organic aerosol composition and evolution in the atmosphere

A. P. Tsimpidi1, V. A. Karydis1, A. Pozzer1, S. N. Pandis2,3, and J. Lelieveld1,4 A. P. Tsimpidi et al.
  • 1Max Planck Institute for Chemistry, Mainz, Germany
  • 2Department of Chemical Engineering, University of Patras, Patras, Greece
  • 3Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA
  • 4Energy, Environment and Water Research Center, Cyprus Institute, Nicosia, Cyprus

Abstract. A computationally efficient module to describe organic aerosol (OA) partitioning and chemical aging has been developed and implemented into the EMAC atmospheric chemistry–climate model. The model simulates the formation of secondary organic aerosol (SOA) from semivolatile (SVOCs), intermediate-volatility (IVOCs), and volatile organic compounds (VOCs). It distinguishes SVOCs from biomass burning and all other combustion sources using two surrogate species for each source category with an effective saturation concentration at 298 K of C* = 0.1 and 10 μg m−3. Two additional surrogate species with C* = 103 and 105 μg m−3 are used for the IVOCs emitted by the above source categories. Gas-phase photochemical reactions that change the volatility of the organics are taken into account. The oxidation products (SOA-sv, SOA-iv, and SOA-v) of each group of precursors (SVOCs, IVOCs, and VOCs) are simulated separately to keep track of their origin. ORACLE efficiently describes the OA composition and evolution in the atmosphere and can be used to (i) estimate the relative contributions of SOA and primary organic aerosol (POA) to total OA, (ii) determine how SOA concentrations are affected by biogenic and anthropogenic emissions, and (iii) evaluate the effects of photochemical aging and long-range transport on the OA budget. We estimate that the global average near-surface OA concentration is 1.5 μg m−3 and consists of 7% POA from fuel combustion, 11% POA from biomass burning, 2% SOA-sv from fuel combustion, 3% SOA-sv from biomass burning, 15% SOA-iv from fuel combustion, 28% SOA-iv from biomass burning, 19% biogenic SOA-v, and 15% anthropogenic SOA-v. The modeled tropospheric burden of OA components is 0.23 Tg POA, 0.16 Tg SOA-sv, 1.41 Tg SOA-iv, and 1.2 Tg SOA-v.

Short summary
A computationally efficient module for the description of OA composition and evolution in the atmosphere has been developed. This module subdivides OA into several compounds based on their source of origin and volatility, allowing the quantification of POA vs. SOA as well as biogenic vs. anthropogenic contributions to OA concentrations. Such fundamental information can shed light on long-term changes in OA abundance, and hence project the effects of OA on future air quality and climate.