Analysis of tropospheric trace gas amounts from satellite and ship-based DOAS-type measurements: NO2 from biomass burning and other sources Mag.rer.nat. Ing. Stefan Friedrich Schreier Dissertation zur Erlangung des Grades Doktor der Naturwissenschaften (Dr.rer.nat.) Institut für Umweltphysik Fachbereich Physik und Elektrotechnik Universität Bremen Oktober 2014 1. Gutachter: Prof. Dr. John P. Burrows 2. Gutachter: Prof. Dr. Justus Notholt Betreuer: Dr. Andreas Richter Dissertation eingereicht am: 13. Oktober 2014 Datum des Kolloquiums: 11. Dezember 2014 ii Du kannst dein Leben nicht verlängern und du kannst es auch nicht verbreitern. Aber du kannst es vertiefen. Gorch Fock, 1880-1916 iii iv Abstract Nitrogen oxides (NOx) play key roles in atmospheric chemistry, air pollution, and climate. While the largest fraction of these reactive gases is released by anthropogenic emission sources, a significant amount can be attributed to vegetation fires. Tropospheric nitrogen dioxide (NO2) amounts can be retrieved from ground-based, ship-based, aircraft-based, and satellite-based remote sensing measurements. The focus of this thesis is to analyze such NO2 measurements for the characterization of NOx from open biomass burning and other sources. In the first part of this thesis, satellite measurements of tropospheric NO2 from GOME-2 and OMI as well as fire radiative power (FRP) from the MODIS instruments are used to derive seasonally averaged fire emission rates (FERs) of NOx for different types of vegetation using a simple statistical approach. Monthly means of tropospheric NO2 vertical columns (TVC NO2) are analyzed for their temporal correlation with the monthly means of FRP for a multi-year period. The strongest correlation is found to be largely confined to tropical and subtropical regions, which account for more than 80% of yearly burned area, on average, globally. As atmospheric models typically require values for the amount of NOx being released as a function of time, the retrieved TVC NO2 is converted into production rates of NOx from fire (Pf). By separating the monthly means of Pf and FRP according to land cover type, FERs of NOx could be derived for different biomes and regions. The estimated FERs for the dominating types of vegetation burned −1 are lowest for boreal forest, open shrublands, and savannas (0.25–1.03 g NOx s −1 −1 −1 MW ) and highest for croplands and woody savannas (0.82–1.56 g NOx s MW ). This analysis demonstrates that the strong empirical relationship between TVC NO2 and FRP and the following simplified assumptions are a useful tool for the characterization of NOx emission rates from vegetation fires in the tropics, subtropics, and in boreal regions. As current fire emission inventories apply emission factors (EFs) of NOx for the translation of biomass burned into trace gas emissions, the satellite-derived FERs of NOx are converted into EFs of NOx. A comparison with NOx EFs found in the literature shows good agreement for some biomes (e.g. boreal forest, tropical forest, and crop residue). v However, the EFs for savanna and grassland obtained from satellite measurements are lower by a factor of 2.5. This has possible implications for future work in this field, in particular because savanna and grassland is the most frequently burned biome on Earth. As recent satellite-based studies have indicated substantial spatio-temporal variations in NOx EFs for several biomes, a modified approach is used for the computation of monthly resolved FERs of NOx. In order to evaluate the impact when such seasonal changes are not included, a case study for the African continent to estimate total NOx emissions from open biomass burning is performed by applying both seasonally averaged and monthly resolved FERs of NOx. The results indicate differences between the two tested approaches of up to 90%, in particular on a monthly basis. In the second part of this thesis, ship-based MAX-DOAS measurements performed within the SHIVA campaign in November 2011 on board RV Sonne in the South China and Sulu Sea are analyzed. Spectral measurements for a total of eleven days are used to retrieve tropospheric slant column densities (SCDs) of NO2 and sulfur dioxide (SO2) in the marine environment. An improved NO2 fit including a cross section for liquid water and an empirical correction spectrum accounting for the effects of liquid water and vibrational Raman scattering and a novel SO2 fit are applied to the ship-based measurements. The conversion of SCDs into TVC NO2 is achieved using both a simple geometric approach and the Bremian advanced MAX-DOAS Retrieval Algorithm (BREAM), which is based on the optimal estimation method and accounts for atmospheric radiative transfer. The results show that the geometric approach using the 15° measurements is in good agreement with BREAM, revealing that measurements at 15° elevation angle can be used for retrieving TVC NO2 in tropical marine environments. 15 -2 As expected, the values of TVC NO2 are generally low (< 0.5 x 10 molec cm ) when no sources of NOx were in proximity to the RV Sonne. However, increased values of 15 -2 TVC NO2 (> 2 x 10 molec cm ) are observed in the morning when the RV Sonne was heading along the coast of Borneo. This is in good agreement with satellite measurements. Interestingly, elevated tropospheric SO2 amounts for measurements taken in a busy shipping lane are consistent with the time series of tropospheric NO2. vi Publications Large parts of this thesis, including text passages, figures, and tables, are based on and/or cited from peer reviewed research articles, oral and poster presentations produced during the thesis. Individual sections that contain such text passages, figures, and tables from published articles, are indicated by an asterisk and appropriate footnotes throughout this thesis. Articles in peer-reviewed journals Schreier, S. F., Richter, A., Kaiser, J. W., and Burrows, J. P.: The empirical relationship between satellite-derived tropospheric NO2 and fire radiative power and possible implications for fire emission rates of NOx, Atmospheric Chemistry and Physics, 14, 2014a. Schreier, S. F., Richter, A., Schepaschenko, D., Shvidenko, A., Hilboll, A., and Burrows, J. P.: Differences in satellite-derived NOx emission factors between Eurasian and North American boreal forest fires, Atmospheric Environment (In Press), 2014b. Alvarado, L. M. A., Richter, A., Vrekoussis, M., Wittrock, F., Hilboll, A., Schreier, S. F., and Burrows, J. P.: An improved glyoxal retrieval from OMI measurements, Atmospheric Measurement Techniques Discussions, 7, 5559-5599, 2014. Schreier, S. F., Peters, E., Richter, A., Lampel, J., Wittrock, F., Burrows, J. P.: Ship- based MAX-DOAS measurements of tropospheric NO2 and SO2 in the South China and Sulu Sea, Atmospheric Environment (under review), 2014c. Schreier, S. F., Richter, A., and Burrows, J. P.: Estimates of NOx emission factors from GOME-2 measurements for the major types of open biomass burning, in: Springer Briefs in Earth System Sciences: Towards an interdisciplinary approach in Earth System Science: Advances of a Helmholtz Graduate Research School, edited by Lohmann, G., Meggers, H. , Unnithan, V., Wolf-Gladrow, D., Notholt, J., and Bracher, A., Springer, Heidelberg (under review), 2014d. vii Selected oral presentations at conferences and workshops Schreier, S. F.: Estimates of forest fire NOx emissions in Russia between 1998 and 2010. Young Scientists Summer Program Workshop, International Institute for Applied Systems Analysis, Laxenburg, Austria, August 2012. Schreier, S. F.: Vegetation fire emission coefficients derived from MODIS fire radiative power and GOME‐2 tropospheric NO2 measurements. Helmholtz Research School on Earth System Science, Annual Retreat, “Deutsches Auswandererhaus“, Germany, November 2012. Schreier, S. F.: Estimation of NOx emissions from vegetation fires based on the empirical relationship between tropospheric NO2 and fire radiative power. AGU Fall Meeting, San Francisco, USA, December 2013. Selected poster presentations at conferences and workshops Schreier, S. F., Richter, A., Schönhardt, A., Burrows J. P.: Relationship between satellite-observed active fires and tropospheric NO2. EGU General Assembly, Vienna, Austria, April 2012. Schreier, S. F., Richter, A., Kaiser, J. W., Burrows J. P.: Biome-specific fire emission rates of NOx from MODIS fire radiative power and GOME-2/OMI tropospheric NO2 satellite-derived data sets. EGU General Assembly, Vienna, Austria, April 2013. Schreier, S. F., Richter, A., Kaiser, J. W., Burrows J. P.: Using satellite measurements of tropospheric NO2 and fire radiative power to derive biome-specific fire emission rates of NOx. Davos Atmosphere and Cryosphere Assembly, Davos, Switzerland, July 2013. Schreier, S. F., Richter, A., Schepaschenko, D., Shvidenko, A., Hilboll, A., Burrows, J. P.: Differences in NOx emission factors between Eurasian and North American boreal forest fires. Helmholtz Research School on Earth System Science, Annual Retreat, “Botanika Bremen“, Germany, November 2013. viii Schreier, S. F., Peters, E., Richter, A., Wittrock, F., Burrows, J. P.: Ship-based MAX- DOAS measurements of nitrogen dioxide in the South China and Sulu Sea. EGU General Assembly, Vienna, Austria, April 2014. Schreier, S. F., Richter, A., Kaiser, J. W., Schepaschenko, D., Shvidenko, A., Hilboll, A., Burrows, J. P.: NOx emission factors from GOME-2 measurements for the major types of open biomass burning. EGU General Assembly, Vienna, Austria, April 2014. Schreier,