In-Flight Measurement of Aircraft Non-Methane Hydrocarbon Emission Indices

Concentrations of non-methane hydrocarbons (NMHC) and CO were measured in exhaust plumes of the DLR experimental aircraft ATTAS equipped with Rolls Royce M 45H MK501 engines. The emission indices (EI) of individual light NMHC were determined from ratios of NMHC and CO concentration enhancements measured in grab samples and the concurrent in-flight measurements of EI of CO by FTIR emission spectroscopy. Alkenes and alkynes generated by cracking of larger NMHC molecules and aromatic compounds originating from unburnt fuel constituted a larger and a smaller fraction of the NMHC emissions, respectively

Alkyl nitrate photochemistry during the tropospheric organic chemistry experiment

Alkyl nitrates (C1-C5) were measured at two sites (near urban and rural) in southeast England during the Tropospheric Organic Chemistry Experiment (TORCH). Methyl nitrate was the dominant species during both campaigns accounting for on average about one third of the total measured alkyl nitrates. High mixing ratios (>50 pptv) and variability of methyl nitrate were observed at the near urban site (TORCH1) that were not seen at the rural site (TORCH2) and which could not be explained by local photochemical production or direct emissions. The diurnal variation of methyl nitrate during TORCH1 showed a morning maximum that would be consistent with nighttime chemistry followed by transport to the surface by boundary layer dynamics. Similarly, elevated morning mixing ratios were also observed during TORCH2 although the magnitudes were much smaller. As a result, methyl nitrate could represent a tracer for nighttime chemistry seen at the ground the following day. At both campaigns, the dominant source of short chain alkyl nitrates and carbonyl precursor radicals (=C4) were from decomposition of larger compounds. The magnitude of the source increased with decreasing carbon number consistent with increasing total precursor abundance. Non-photochemical emissions of acetaldehyde and acetone could not be accounted for by automobile exhaust emissions alone and indicated that other direct sources are likely important in this environment

Ozone photochemistry during the UK heat wave of August 2003

A wide range of chemical and physical parameters have been observed over the course of a severe Europe-wide air pollution episode in August 2003. Detailed surface observations made at the rural perimeter edge of London, U.K. indicated significantly elevated levels of primary VOCs, ozone (>110ppb), other photochemical by-products such as PAN, HCHO, and higher oxygenates but not NOx. Reactive organic tracers in combination with surface Doppler wind radar and back trajectory analysis have been used to establish that initial rapid morning rises in O3 during the episode were caused by entrainment of air from aloft, polluted on regional scales from mainland Europe. Total VOC reactivity to OH approximately doubled during this episode, with similar distribution between functional groups, but showing a temperature dependant exponentially increasing contribution from biogenic isoprene (max 1.2 ppbV). In addition to entrainment of regional air pollution, ozone formation rates within the U.K. boundary layer on the day of observation have been determined using measured peroxy radicals in combination with other chemical data. Under episodic conditions total peroxy radicals in excess 120pptV were observed in late afternoon with strong correlation to a later and higher peak in ozone when compared to non-episodic conditions. During the daytime under episodic conditions alkyl peroxy radical formation was dominated by PAN thermolysis, whose afternoon lifetime averaged only 18.3 min, but which was sustained at a concentration greater than 750 pptV. Low episodic wind speeds resulted in a relatively small possible spatial footprint for emissions of reactive precursors to PAN, and a strong correlation between isoprene and PAN production rate suggest this species may have contributed to the later afternoon increases seen in surface O3