Table 1.

Relative percentage change in AOD at 550 nm during March–May 2018–2020. (where: 2020/2019 is ratio of 2020 vs 2019, 2020/2018 is ratio of 2020 vs 2018).

	2018/2020			2019/2020
	March	April	May	March	April	May
Warsaw	–	−63.2	−46.7	60	−50	−33.3
Gdansk	–	−82.4	–	–	−84.2	–
Lodz	–	−33.3	−35.7	37.5	−53.8	28.6
Krakow	–	−30.8	−47.1	61.5	−10	−40
Poznan	–	−65.4	−8.3	120	−50	–
Wroclaw	–	−26.7	−21.1	90.9	−26.7	50