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Ozone (O3) and aerosol scattering ratio profiles were obtained from airborne lidar measurements on thirty‐eight flights over seven deployments covering the latitudes of 40°–85°N between 4 February and 23 May 2000 as part of the Tropospheric Ozone Production about the Spring Equinox (TOPSE) field experiment. Each deployment started from Broomfield, Colorado, with bases in Churchill, Canada, and on most deployments, Thule Air Base, Greenland. Nadir and zenith lidar O3 measurements were combined with in situ O3 measurements to produce vertically continuous O3 profiles from near the surface to above the tropopause. Potential vorticity (PV) distributions along the flight track were obtained from several different meteorological analyses. Ozone, aerosol, and PV distributions were used together to identify the presence of pollution plumes and stratospheric intrusions. Ozone was found to increase in the middle free troposphere (4–6 km) at high latitudes (60°–85°N) by an average of 4.6 ppbv/mo (parts per billion by volume per month) from about 54 ppbv in early February to over 72 ppbv in mid‐May. The average aerosol scattering ratios at 1064 nm in the same region increased rapidly at an average rate of 0.36/mo from about 0.38 to over 1.7. Ozone and aerosol scattering were highly correlated over the entire field experiment, and PV and beryllium (7Be) showed no significant positive trend over the same period. The primary cause of the observed O3 increase in the mid troposphere at high latitudes was determined to be the photochemical production of O3 in pollution plumes with less than 20% of the increase from stratospherically‐derived O3.

The Tropospheric Ozone Production about the Spring Equinox (TOPSE) experiment examined the evolution of tropospheric chemical compositions from February to May 2000 over North America, 40 to 85 N. Hydrogen peroxide (H2O2) and methyl hydroperoxide (CH3OOH) were investigated using instrumental observations aboard the NCAR C-130 research aircraft. Primary TOPSE results indicate both photochemistry and atmospheric dynamics are critical factors controlling the variability of peroxides in this region. From February to May, H2O2 and CH3OOH mixing ratios increased with the greatest relative changes at mid-altitudes. H2O2 ranged from below the detection limit (BDL = 25 pptv) to 380 pptv in winter and from BDL to 1330 pptv during spring. Winter measurements of CH3OOH were from BDL (35 pptv) to 740 pptv with higher levels of BDL to 1400 pptv measured during spring. Peroxides also decreased with latitude at all altitudes. These findings are consistent with those expected from photochemical theory. Evidence also supports a source of CH3OOH to the Arctic from the transport of subtropical air masses. Air mass back trajectories and GOES-derived specific humidity products indicate transport of moist tropical air to the study region coincides with elevated levels of CH3OOH up to 940 pptv. The concurrence of this transport regime with episodic elevated CH3OOH events suggests a source of HOx to the Arctic. However, evidence from this study shows CH3OOH does not greatly contribute to total HOx production which is dominated primarily by reactions of O(lD) and H2O at low latitudes and CH2O at high latitudes.