An investigation into the source of the springtime tropospheric ozone maximum at Mauna Loa Observatory

Measurements of CH 4 , CO, O 3 , and H 2 O vapor from Mauna Loa Observatory (MLO) are examined in conjunction with isentropic trajectories to investigate the cause of a maximum in tropospheric O 3 consistently observed during spring. CO and O 3 have been found to be positively correlated in pollution plumes containing O 3 precursors downwind of industrialized regions. However, we report that during continental transport from Asia, O 3 is not correlated with either CO or CH 4 , although CO and CH 4 are strongly correlated. The relationship between CO and CH 4 suggests common source regions. The lack of correlation between these species and O 3 probably indicates an O 3 source distinct from that of CO and CH 4 . While Asian pollution does not appear to be a strong candidate for causing the spring increase in O 3 , transport characteristics and H 2 O vapor measurements are consistent with both an upper‐tropospheric/stratospheric contribution and an enhancement from transport across O 3 gradients.