- Wang, Y
- Ridley, B
- Fried, A
- Cantrell, C
- Davis, D
- Chen, G
- Snow, J
- Heikes, B
- Talbot, R
- Dibb, J
- Flocke, F
- Weinheimer, A
- Blake, N
- Blake, D
- Shetter, R
- Lefer, B
- Atlas, E
- Coffey, M
- Walega, J
- Wert, B
- et al.
Physical and chemical properties of the atmosphere at 0-8 km were measured during the Tropospheric Ozone Production about the Spring Equinox (TOPSE) experiments from February to May 2000 at mid (40°-60°N) and high latitudes (60°-80°N). The observations were analyzed using a diet steady state box model to examine HO and O photochemistry during the spring transition period. The radical chemistry is driven primarily by photolysis of O and the subsequent reaction of O( D) and H O, the rate of which increases rapidly during spring. Unlike in other tropospheric experiments, observed H O concentrations are a factor of 2-10 lower than those simulated by the model. The required scavenging timescale to reconcile the model overestimates shows a rapid seasonal decrease down to 0.5-1 day in May, which cannot be explained by known mechanisms. This loss of H O implies a large loss of HO resulting in decreases in O production (10-20%) and OH concentrations (20-30%). Photolysis of CH O, either transported into the region or produced by unknown chemical pathways, appears to provide a significant HO source at 6-8 km at high latitudes. The rapid increase of in situ O production in spring is fueled by concurrent increases of the primary HO production and NO concentrations. Long-lived reactive nitrogen species continue to accumulate at mid and high latitudes in spring. There is a net loss of NO to HNO and PAN throughout the spring, suggesting that these long-term NO reservoirs do not provide a net source for NO in the region. In Situ O chemical loss is dominated by the reaction of O and HO , and not that of O( D) and H O. At midlatitudes, there is net in situ chemical production Of O from February to May. The lower free troposphere (1-4 km) is a region of significant net O production. The net production peaks in April coinciding with the observed peak of column O (0-8 km). The net in situ O production at midlatitudes can explain much of the observed column O increase, although it alone cannot explain the observed April maximum. In contrast, there is a net in situ O loss from February to April at high latitudes. Only in May is the in situ O production larger than loss. The observed continuous increase of column O at high latitudes throughout the spring is due to transport from other tropospheric regions or the stratosphere not in situ photochemistry. x 3 3 2 2 2 2 2 x 3 2 x 3 x x 3 x x 3 3 2 2 3 3 3 3 3 3 3 3 1 1