Can Aircraft-Based Remote-Sensing NO₂ Measurements Combined with High Resolution Model Data Improve NO₂ Exposure Estimates over Urban Areas?

Abstract

As part of the STEREO-III BUMBA (Belgian Urban NO₂ Monitoring Based on APEX hyperspectral data) project, we try to exploit the synergy between NO₂ column measurements derived from the aircraft-based APEX hyperspectral imaging system and high-resolution model data from a combined land use regression-Gaussian plume model system for the complex city-port region of Antwerp (Belgium). The resulting model maps are then used to determine the NO₂-exposure of the population of the region.

Several difficulties are encountered when attempting to reconcile measurements and model results. These stem from four main different reasons:

• (1) The APEX remote-sensing measurements provide integrated NO₂ columns, while the modelled data are focused on ground-level concentrations.

• (2) The model data typically represent hourly averages, while measurements are instantaneous.

• (3) The model uses time factors in determining the amount of emissions from traffic, industry, etc.

• (4) Additional sources of uncertainties in both the model and the measurements.

In conclusion, our study shows that the use of APEX data to constrain NO₂-exposure estimations is a complex process involving a number of uncertainties that need to be properly characterised. In particular we find that a robust methodology for relating concentration profiles to surface concentrations is needed before aircraft data can eventually help improving the model input data (e.g. time factors). This is further studied in the project.