Emissionen reaktiver Jodverbindungen von Makroalgen (MAORI)
Zusammenfassung der Projektergebnisse
In the MAORI project successful measurements of iodine species and emissions at the New Zealand coast could be performed. Seaweed induced IO was observed by CE-DOAS at Shag Point on the east coast of New Zealand and were the first observation in this area so far.. The detected IO mixing ratios of several 10 ppt are in the same range as mixing ratios observed on typical northern hemisphere sites e.g. Irish west coast around Mace Head. This shows that typical southern hemisphere seaweed species are potent iodine emitters that can reach the necessary mixing ratios to cause iodine induced formation of cloud condensation nuclei and thus influence the local climate as well as the ozone budget. To determine the iodine emission potential of individual species their emission behavior was observed in a closed Teflon chamber built around the CE-DOAS. With these experiments were able to estimate the emission rates of five different Southern Hemisphere seaweed species. Four of the investigated species showed strong emissions with emission rates comparable to seaweed species on the northern hemisphere. Among these potent emitters Macrocystis Pyrifera was most abundant. This species is also the most widely distributed kelp in the world and one of the fastest growing organisms on earth. Being very nutrient rich M. Pyrifera is commercially harvested to an increasing extend. After harvest the kelps are dried before they are further processed. This resembles the exposure during low tide and thus kelp harvesting could make a human contribution to the local IO emission. However the significance of this human source needs to be investigated in further studies. This study focused on the area around Shag Point. To determine the influence of halogen emissions from seaweed on the air chemistry and climate of coastal areas in New Zealand further studies which cover larger areas are necessary. This should be optimally undertaken with a mobile LP-DOAS which would be much more flexible to setup than the stationary instrument used during this campaign in addition to a mobile CE-DOAS measuring IO. It would furthermore be desirable to have a second CE- DOAS or a combined system with a second channel measuring molecular iodine (I2) as this is supposed to be the major iodine emission from seaweeds. Also the chamber studies should be repeated with an improved setup to determine more accurate emission rates. Adding a controlled air exchange in the chamber will reduce the major error source in the determination of IO emission rates. It will also give the possibility to measure the same sample at different exchange times and thus allow to determine the contribution of the IO self reaction to the losses. Also a new ozone monitor with a better accuracy and time resolution will be important to determine if ozone degradation is a limiting factor for the measured emission rates.
