Those are summer numbers, they also given winter numbers of China: 25%, Western Europe: 10%, India: 6%. The article is kind enough to link to the study: https:

Those are summer numbers, they also given winter numbers of China: 25%, Western Europe: 10%, India: 6%. The article is kind enough to link to the study: https://www.science.org/doi/10.1126/sciadv.abm9909 https://www.science.org/doi/10.1126/sciadv.abm9909 The data is coming from satellites, which are apparently able to directly measure NO2 levels (a good proxy for NOx levels), and they use near infrared reflectivity to estimate crop yield (which they say previous studies have shown to be a good way to estimate it).