---

Nitrogen bearing compounds play an important role in catalytic loss of stratospheric ozone and will become even more important in future. Here balloon-borne limb measurements of the time and altitude dependent variation of O3, NO2, BrO and HONO are presented, providing new insight into the NOx and NOy photochemistry of the tropical upper troposphere, lower and middle stratosphere. A new method is discussed aiming at the retrieval of the diurnal variation of UV/vis absorbing radicals. The method employs spectroscopic measurements in combination with radiative transfer modeling and a mathematical inversion on a regularized time and height grid. The retrieval is tested by comparing the results to in-situ ozone sonding, simultaneous O3, NO2 and BrO direct sun observations and to measurements of the ENVISAT/SCIAMACHY satellite instrument. The collected data are further explored to in-situ test photochemical parameters, critical for stratospheric ozone, exemplarily for the N2O5 photolysis rate.Finally, first detection of HONO in the tropical upper troposphere is reported, and discussed in the context of NOx formation in thunderstorms.

---

Lena Kritten was born in Berlin in 1979. She studied Physics atthe University of Heidelberg and wrote a Diplomathesis at the Institute of environmental Physics aboutspectroscopic measurements at the hawaiin volcano Kilauea.For her PHD she applied the same measurement technique to studystratospheric photochemistry in the northeast of Brazil.

---