Model description

ADCHEM (2D-Lagrangian Model for Aerosol Dynamics, Gas-Phase Chemistry and Radiative Transfer) is a 2D-Lagrangian model for Aerosol Dynamics, gas phase CHEMistry and radiative transfer, which uses 1-order turbulence closure schemes to describe the air mass mixing in the vertical and horizontal direction perpendicular an air mass trajectories (Figure 1).

ADCHEM incorporates a 2-stream approximation scheme for radiative transfer in inhomogeneous atmosphere with aerosols and clouds. This enables the model to calculate the radiative forcing caused by aerosols and clouds.

The model also includes:

  • all important aerosol dynamic processes (homogeneous nucleation, coagulation, condensation, dry deposition);
  • in-cloud aerosol processing and below cloud scavenging;
  • a thermodynamic particle-phase chemistry module;
  • near explicit gas-phase chemistry with reactions from Master Chemical Mechanism, MCMv3.2 (;
  • a kinetic multilayer model for treatment of mass-transfer limitations in the particle-phase.

The SOA formation can either be modelled with a non-equilibrium 2D-Volatility Basis Set approach[1] or by considering the condensation of the MCM gas-phase oxidation products. This offers an opportunity to compare and improve both these methods [2].

The model source code is available both in MATLAB and Fortran-90.

Model application (examples)

ADCHEM has been used to study the ageing of the urban plume downwind the city of Malmö (~300 000 inhabitants). Downwind Malmö the freshly emitted soot particles are coated with SOA and ammonium nitrate. The model results reveal a substantial ammonium nitrate formation downwind Malmö (Figure 2a). This is governed by a combination of high NH3 emissions from the agricultural sector and emissions of NOx from the road traffic in Malmö[3]. The combination of high soot primary particle number emissions, SOA and ammonium nitrate formation contributes to a substantial amplification of the number of CCN downwind Malmö (Figure 2b). In the centre of the urban plume, 50 km (~3 h) downwind Malmö, the emissions in Malmö contributes to ~30 % (~1000 cm-3) of the total particle number concentration. The maximum secondary aerosol mass enhancement of ~0.8 μg m-3 is reached later (6-18 hours downwind Malmö).

ADCHEM is also used to study the formation and growth of homogeneously nucleated particles. Figure 3 illustrates an example of modelled and measured particle properties during a 9 day period with frequent new particle formation events at the Vavihill field station in Southern Sweden. The model results at the field station was acquired by running the model along 7 days backward air mass-trajectories, arriving at the station with 3 hour intervals (in total 72 simulations). The model captures the diurnal trends in the particle number and volume concentrations, although the model sometimes overestimates the total number of particles larger than 3 nm in diameter (Fig 3e-f).

Figure 1. Schematic picture illustrating the ADCHEM 2D-model domain which follow an air mass trajectory in time.

Figure 2. (a) Modelled secondary aerosol nitrate formation along an air mass trajectory moving over the city of Malmö (~300 000 inhabitants). The black line displays the altitude of the planetary boundary layer. (b) Modelled potential Cloud Droplet Number enhancement (ΔCDN) caused by gas- and primary particle emissions in the city of Malmö.

Figure 3. Modelled and measured particle properties during a 9 day period at the Vavihill field station is Southern Sweden.