Seasonal variations of diurnal cycles of aerosols and gases in the Fukuoka Plain, Japan: Effects of local meteorology and atmospheric chemistry

Simultaneous measurements of wind profiles and of atmospheric substances such as aerosols and reactive gases were conducted at Fukuoka University in the western urban area of Japan to elucidate relations between local circulation and variations of aerosols and gases. Spatial variations of wind speed and direction over the Fukuoka Plain were measured using Doppler LIDAR. Some atmospheric substances such as black carbon, organic carbon, CO, and NOx were found to have maxima in morning (07–11 JST) and evening (18–20 JST), when diurnal cycles of wind direction and speed were observed near the surface. Doppler LIDAR data indicated clearly that the diurnal cycles of wind profiles were associated with sea breezes and land breezes over the Fukuoka Plain. The diurnal variations of aerosols and gases might be attributed to local anthropogenic emissions such as vehicle exhaust from Fukuoka city and vessels in the Hakata Bay and the sea and land breeze cycles. Strengths of morning peaks and evening peaks showed clear seasonal changes, with stronger peaks during the colder seasons and weaker peaks during the warmer and hot months. Slopes related to BC, OC, NOx, and CO were found to have seasonal changes. These seasonal changes were associated with the presence of a surface inversion layer in colder seasons, efficient photochemical reactions in the summer, and changes of fuel emission factors.