Trajectory Assisted Analysis of Long-Term Ozonesonde Data Over N. America: A Comparison With Europe and East Asia

Changes in tropospheric ozone over one continent are controlled by photochemistry and meteorology within that continent and also by long-range transport from other continents. Knowledge of background ozone concentration over individual continent plays an important role in such studies. Therefore it is important to establish a suitable and versatile methodology, which could estimate the changes in background ozone at one continent and also estimate the contribution of regional pollutions from other continents. In this direction, we had successfully analyzed long-term ozonesonde data from Europe (Hohenpeissenberg, and Payerne) and Japan (Sapporo, Tateno, Kagoshima, and Naha) using residence time and sectoral classification, which were deduced from backward isentropic trajectories. Here, we present recently analyzed ozonesonde data from Boulder (40.0N, 105.0W, 1689m), Wallops (38.0N, 75.5W, 13m) and Hilo (19.7N, 155.1E, 11m) for the boundary layer (BL) and lower troposphere (LT). We have classified two types of ozone namely, regionally polluted ozone and background ozone. Regionally polluted ozone shows similar seasonal variation over Wallops and Boulder with maximum ozone in late spring and early summer. Background ozone levels in USA boundary layer are estimated to be lesser (by 10 ppbv), when compared with regionally polluted ozone levels over USA. Surprisingly, background (pacific air-mass) ozone levels over Hilo, USA are higher than the ozone levels for similar type of air-masses over Japanese sites. Unlike over Europe, ozone levels over USA do not show very significant correlation with residence time of air-masses. Long-term changes in regionally polluted ozone over Wallops and Boulder are nearly similar and appear to show some consistency with NOx emissions over USA. More results will be discussed during presentation.