select kiedy, ROUND(AVG(pm10),2) AS pm10, ROUND(AVG(pm2_5),2) AS pm2_5, LEFT(kiedy,14) AS kied from czujniki where  pm10>-1 and czujnikid=8840265 and kiedy<>'0000-00-00 00:00:00' GROUP BY kied order by pm10 desc limit 1