free of clouds, while there is a white cloud wall further inland, which can cause rain showers. Air quality The air quality in Espoo is considerably good despite the negative effect of the traffic. Particularly on pedestrian roads, sand is used to combat slipperiness, which causes a major dust problem in springtime. Studded tires also contribute to the number of harmful particles. The air quality in Espoo is measured in Leppävaara and Luukki. There are also mobile measurement stations. Alder and birch pollen has a harmful effect on the air quality in springtime, hay and mugwort in summertime. Lighting conditions Espoo is located at a latitude of 60 degrees north, which causes the duration of daylight to vary considerably. At summer solstice daylight lasts for nineteen hours, while at winter solstice it only lasts for six hours. The angle of the sun is at its highest at 53.4 degrees in summertime and only at 6.6 degrees in wintertime. Espoo is among the northernmost places to have nautical dusk even at summer solstice, meaning the sun is at least six degrees below the horizon at the darkest hour of the night. At that time, there is no total darkness during the entire night. In contrast, daylight at winter solstice is short, especially when there are only few sunny hours from November to January. Shadows cast by buildings are long even at summertime. They are at their shortest at summer solstice, about 75 percent of the height of the buildings. For example, the shadow of Niittyhuippu is 63 metres long at the time. At noon at winter solstice the shadows can be up to 8.8 times the height of the entire building. For example, the shadow of the Tapiola Central Tower is 430 metres long at the time. The official time in Espoo is measured by the 30th eastern meridian. The city is located over five degrees west of it, so the solar noon occurs over 20 minutes later than on the 30th meridian. Growth season Espoo is located at the plant success zone 1b. The thermal growth season lasts for a bit over half a year on average. In general, the growth season starts in April and ends in October. Sometimes it continues to early November. The sum of the effective temperature during the thermal growth season is over 1,400 degrees Celsius times day, and annual variations are large. Administration Espoo