Study of Air Transport and Photochemistry in the North-Atlantic Region by Hydrocarbon Analysis at Pico Island, Azores
Several recent large-scale atmospheric chemistry experiments have demonstrated that intercontinental transport of air pollution has a remarkable impact on regional air quality and that synoptic transport of pollution from Asia to North America as well as from North America to Western Europe needs to be considered in the understanding and management of air quality in these continents. While these episodic campaigns have yielded information of such transport phenomena, the desired improvement of our understanding of the occurrence, seasonality and control of long-range air transport requires continuous, year-round measurements at coastal and remote marine monitoring sites.
The PICO-NARE monitoring station is located near the summit of Pico Island in the Azores, Portugal, and has been developed by Michigan Technological University (R. Honrath) and the University of the Azores (P. Fialho). NARE, the North Atlantic Regional Experiment, is part of the Intercontinental Transport and Chemical Transformation (ITCT) project of the International Global Atmospheric Chemistry (IGAC) program. The particular goals of PICO-NARE are to quantify the impact of exported ozone, nitrogen oxides, and black carbon on the regional atmosphere and to identify the atmospheric transport and photochemical history of the encountered air samples. PICO-NARE is a receptor site for transport from North America as well as from Europe and Africa and has been shown to be a very suitable location for research on long-range transport and atmospheric chemistry from these diverse source regions.
Current measurements at PICO-NARE include carbon monoxide, ozone, Black Carbon, and meteorological parameters. Further measurements that will commence in 2002 are JNO2, NO, NO2, and NOy. A constraining gap in the interpretation of data is the current lack of hydrocarbon measurements. This project addresses this need: We propose to develop continuous (every 2 hours), on-site measurements of volatile organic compounds (VOC) by an automated gas chromatograph (GC) with low parts-per-trillion detection limits. The GC instrument will rely on established sample collection and injection procedures by multi-stage solid adsorbent concentration with thermal desorption. Analysis will be performed by two parallel columns with flame ionization and photoionization detection. Monitored system parameters and GC data will be transferred via ftp to our Boulder laboratory. Quantified VOC will include ethane, ethene, acetylene, propane, propene, methyl-propane, butane, butadiene, methylbutane, dimethylpropane, pentane, isoprene, benzene, toluene, methyl chloride and methyl chloroform, and possibly selected oxygenated hydrocarbons such as acetaldehyde, methanol, acetone and long-chain aldehydes.
Ambient mixing ratios and relative ratios of selected hydrocarbon pairs will be monitored and used as a sensitive tool to derive information on photochemical history and atmospheric transport from emission sources to when the sample was collected. Furthermore, analysis of short-lived compounds, such as isoprene and ethene, is a valuable tool for identifying upslope air originating from vegetated areas of Pico and the marine boundary layer. Correlation of VOC with the observation of the other analyzed gases (see above) and Black Carbon will be investigated.
The measurements proposed in this study will add significant characterization of atmospheric intercontinental transport in the North Atlantic Region. VOC analysis will decipher air mass history, photochemical properties and enhance data analysis capabilities of current measurements. This study will support observations for the year 2004 intensive ITCT-2K4, INTEX-NA and EXPORT-E2 field campaigns and provide a means for extension and interpolation of their results to the seasonal and annual domain.