Evaluating model Nitrogen Dioxide measurements over China

This result is the first validation of modeling Nitrogen dioxide (NO₂) results with the widespread in situ network, which became recently available. Our study demonstrates the capabilities of chemistry-transport models (CTMs) such as CHIMERE, combined with satellite observations from Aura OMI, to simulate NO₂ concentrations at the surface over China.

The validation results reveal the bias of the spatial distribution of bottom-up NO_x emissions inventories and for the first time point out that such bias can be reduced significantly by applying the spatial distribution of NO_x emissions in the OMI-based inventory as the spatial proxy for the bottom-up inventory. This is expected to be generally true for regions all over the world including the US. The accuracy of the OMI-based inventory, DECSO, will substantially be improved over the US with the addition of upcoming geostationary missions, such as NASA's TEMPO instrument, where hourly NO₂ observations provide important diurnal information.

• NO₂ actively participates in the formation of tropospheric ozone & secondary aerosols, which can impact human health & climate significantly.
• Daily OMI NO₂ observations over China are used as a constraint to update NO_x emissions in the DECSO (Daily Emission estimates Constrained by Satellite Observations) inventory.
• The OMI-based corrected DECSO inventory improves the distribution of emissions between urban & suburban/rural areas of China compared to the bottom-up (MIX) inventory alone, reducing the bias between modeled & observed NO₂.
• This is the first validation of modeled NO₂ with this widespread, recently available in situ network.

Technical Description of Figure:
(Top) Annual mean surface NO₂ concentration in 2015 based on the CHIMERE model driven by the MIX Asian inventory (a) and the corrected DECSO inventory (b). The corrected DECSO inventory is scaled emissions over China based on the bottom-up inventory MIX, but with the same DECSO spatial distribution. (Bottom) Scatter plots of the simulated annual mean surface NO₂ concentrations in 2015 by the MIX Asian inventory (a) and the corrected DECSO inventory (b) and the corrected in situ measurements.

Data Sources: We use the CHIMERE model v2013b over East Asia (18 to 50° N and 102 to 132° E) with a resolution of 0.25°, driven by operational meteorological data from the European Centre for Medium- Range Weather Forecasts (ECMWF) with a horizontal resolution of 0.25°. The satellite-derived NO_x emissions were estimated by the algorithm DECSO (Daily Emission estimates Constrained by Satellite Observations) v5 using an extended Kalman filter. Daily OMI NO₂ observations retrieved with the DOMINO version 2 algorithm are used as a constraint to update emissions. The DECSO emission data are available at http://www.globemission.eu. Real-time hourly NO₂ concentrations, recorded by the Ministry of Environmental Protection (MEP) in China and publicly accessible from the year 2013 onwards, were obtained from a total of 1413 air quality monitoring sites of the MEP network for 323 major cities over the model domain.

The bottom-up anthropogenic NO_x emissions were taken from the MIX inventory, a mosaic Asian anthropogenic emission inventory under the international col- laboration framework of the Model Inter-Comparison Study for Asia (MICS-Asia) and the Task Force on Hemispheric Transport of Air Pollution (TF HTAP). The MIX inventory is developed for the years 2008 and 2010 by an integration of state-of-the-art regional emission inventories for all major anthropogenic sources in 29 countries and regions over Asia. The emissions of China integrated in the MIX inventory are derived from the Multi-resolution Emission Inventory for China (MEIC: http://www.meicmodel.org) compiled by Tsinghua University. The anthropogenic emissions with the biogenic emissions, which were computed automatically in the CHIMERE model using the global MEGAN (Model of Emissions of Gases and Aerosols from Nature) model, were adopted as the bottom-up inventory. Note that monthly emissions for all inventories above were provided at the spatial resolution of 0.25° x 0.25° .

References: Liu, F., van der A, R. J., Eskes, H., Ding, J., and Mijling, B.: Evaluation of modeling NO₂ concentrations driven by satellite-derived and bottom-up emission inventories using in situ measurements over China, Atmos. Chem. Phys., 18, 4171-4186, https://doi.org/10.5194/acp-18-4171-2018, 2018.

5.29.2018