Fig. 4.

Time series of the 15-day moving averages of 1-h daily maximum NO₂ (a, b) and MDA8 O₃ (c, d) concentrations at background sites in Germany and Spain. The time series included here correspond to observations during the reference period 15 March – 31 August 2015–2019 (grey), observations during 15 March – 30 April 2020 (red), GAM predictions using daily meteorology of that period (blue) and GAM predictions for the same period after replacing some meteorological fields (daily maximum temperature and specific humidity for Germany, solar radiation and specific humidity for Spain) by 15-day moving averages around each calendar day of 2015–2019 (golden). Solid lines depict the medians across all sites and shading indicates the range between the 25th and 75th percentiles. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)