Satellite-derived estimates of surface ozone by LESO: Extended application and performance evaluation

Abstract

Surface O3 pollution severely threats human health and crop production across the globe. Data-driven machine learning approaches are broadly used for estimating surface O3 concentrations in China by integrating site-level measurements, meteorological reanalysis data, and satellite remote sensing observations. However, the feasibility of extending these approaches from China to the globe requires further investigation, and the sensitivities of different model drivers remain unknown. By using the LEarning Surface Ozone (LESO) framework, this study explores the effectiveness of estimating daily surface O3 over Europe, the United States, and India and analyses the impacts of satellite columns, climate drivers, machine learning algorithms, and in-situ sites on the estimation performance. A cross-validation of the LESO framework against in-situ sites exhibited a promising performance with an mean R2 higher than 0.9 and uncertainty smaller than 4 µg/m3 in Europe and the United States. Due to its success in capturing the O3 variability with a user-friendly interface and less computing resources occupancy, LESO is expected to promote efforts in global O3 pollution monitoring. However, the estimation performance in India was not good enough (R2 9 µg/m3). Regarding potential factors affecting the estimation performance, the satellite O3 columns and the number of in-situ sites did not affect the estimation performance significantly; the use of the deep learning technique improved the performance by 30 % than using a conventional non-deep learning algorithm; and the spatial sampling density of in-situ sites dominantly affected the estimation performance. This can be the reason causing the unsatisfactory performance in India. The findings of this study are beneficial to promoting global surface O3 estimation and can bring evidence on the location selection for deploying new in-situ sites.

Keywords

• Surface ozone pollution
• Remote sensing
• Deep learning