Inhaltszusammenfassung

Since the start of industrialization and increasingly since the 1950s, anthropogenic activities have altered the Earth’s atmospheric composition significantly with consequences for climate, weather, and the health of both humans and ecosystems. Reactive trace gases are, on the one hand, part of the anthropogenic emissions that fuel air pollution and impact climate, and on the other hand, are impacted by the manmade changes in environmental conditions in a feedback loop. A way to quantify...Since the start of industrialization and increasingly since the 1950s, anthropogenic activities have altered the Earth’s atmospheric composition significantly with consequences for climate, weather, and the health of both humans and ecosystems. Reactive trace gases are, on the one hand, part of the anthropogenic emissions that fuel air pollution and impact climate, and on the other hand, are impacted by the manmade changes in environmental conditions in a feedback loop. A way to quantify the total atmospheric load of reactive trace gases is the measurement of total OH reactivity, i.e. the loss rate of the most important tropospheric oxidant, the hydroxyl (OH) radical. In this doctoral project, total OH reactivity measurements were used to investigate two points in the feedback loop of human activity and atmospheric reactants: Firstly, the indirect impact of anthropogenic climate change and deforestation, which will lead to an increasing frequency of drought and heat events in the Amazon rainforest, is thought to influence biogenic trace gas emissions. This was investigated using total OH reactivity observations during an extreme El Niño event. Secondly, direct human impact above the seaways around the Arabian Peninsula, detectable by anthropogenically emitted trace gases from ships and oil/gas production, was studied with total OH reactivity observations and a regional ozone formation assessment. The method-oriented part of this doctoral project was based on the need for robust, accurate long-term observations of total OH reactivity for understanding atmospheric photochemistry in the Anthropocene epoch. During the drought and heat conditions of the extreme 2015/16 El Niño event, the diel cycle of total OH reactivity in the Amazon rainforest exhibited a striking difference to "normal" diel behavior. After the usual early afternoon OH reactivity maximum, a second, higher peak was observed during the sunset hours. A possible explanation for the increased sunset reactivity was found in stronger turbulent transport inside and above the canopy related with the changed meteorological conditions, combined with a stress-related release of monoterpenes and other (unmeasured) BVOCs by vegetation. Total OH reactivity measured around the Arabian Peninsula was comparable to highly populated urban areas, due to a combination of shipping emissions and petrochemical pollution. The extreme regional ozone concentrations could be explained by a favorable mixture of NOx and VOCs coupled with intense solar irradiation, causing rapid photochemical reactions. A new Comparative Reactivity Method (CRM) instrument for long-term autonomous measurements of total OH reactivity was successfully characterized and tested in Helsinki. Interferences were quantified and compared to a model of the CRM reactor chemistry. The total OH reactivity observed in winter in Helsinki was with an overall median of 7.6 s^−1 at the lower end of worldwide urban observations. In the first comprehensive intercomparison of OH reactivity measurements, the CRM method was compared to all other available instrument types by simultaneous measurements at an atmospheric simulation chamber. Results showed that the CRM device is suited for a range of atmospheric mixtures. However, significant deviations were seen under terpene-dominated and high NO conditions. A sensitivity towards ozone, which also impacted the size of the NO2 interference, was newly discovered for CRM. Photolysis inside the reactor and the HO2 concurrently produced with OH were identified as major sources of interferences and uncertainties. With the aim of improving the method, laboratory studies were conducted in the aftermath of the intercomparison, focusing on reducing photolysis and increasing CRM sensitivity.» weiterlesen» einklappen

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DDC Sachgruppe:
Geowissenschaften