MICS-Asia III : Multi-model comparison and evaluation of aerosol over East Asia

Fourteen chemical transport models (CTMs) participate in the MICS–Asia Phase III Topic 1. Their simulation results are compared with each other and with an extensive set of measurements, aiming to evaluate the current multi–scale air quality models’ ability in simulating aerosol species and to document similarities and differences among model performances, also to reveal the characteristics of aerosol chemical components over big cities in East Asia. In general, all participant models can reproduce the spatial distribution and seasonal variability of aerosol concentrations in the year 2010, and multi–model ensemble mean (EM) shows better performance than most individual models, with Rs ranging from 0.65 (NO³⁻) to 0.83 (PM_2.5). Underestimations of BC (NMB = −17.0 %), SO₄²⁻ (NMB = −19.1 %) and PM₁₀ (NMB = −32.6 %) are simulated by EM, but positive biases are shown in NO³⁻ (NMB = 4.9 %), NH₄⁺ (NMB = 14.0 %) and PM_2.5 (NMB = 4.4 %). Simulation results of BC, OC, SO₄²⁻, NO₃⁻ and NH₄⁺ among CTMs are in good agreements, especially over polluted areas, such as the eastern China and the northern part of India. But large coefficients of variations (CV > 1.5) are also calculated over arid and semi–arid regions. This poor consistency among CTMs may attribute to their different processing capacities for dust aerosols. According to the simulation results in the six Asian cities from EM, different air–pollution control plans should be made due to their different major air pollutants in different seasons. Although a more considerable capacity for reproducing the concentrations of aerosol chemical compositions and their variation tendencies is shown in current CTMs by comparing statistics (e.g. RMSE and R) between MICS–Asia Phase II and Phase III, detailed process analysis and a fully understanding of the source–receptor relationship in each process may be helpful to explain and to reduce large diversities of simulated aerosol concentrations among CTMs, and these may be the potential development directions for future modeling studies in East Asia.