Night-time chemistry above London: measurements of NO[subscript 3] and N[subscript 2]O[subscript 5] from the BT Tower

Broadband cavity enhanced absorption spectroscopy (BBCEAS) has been used to measure the sum of concentrations of NO[subscript 3] and N[subscript 2]O[subscript 5] from the BT (telecommunications) Tower 160 m above street level in central London during the REPARTEE II campaign in October and November 2007. Substantial variability was observed in these night-time nitrogen compounds: peak NO[subscript 3] and N[subscript 2]O[subscript 5] mixing ratios reached 800 pptv, whereas the mean night-time NO[subscript 3] and N[subscript 2]O[subscript 5] was approximately 30 pptv. Additionally, [NO[subscript 3] and N[subscript 2]O[subscript 5]] showed negative correlations with [NO] and [NO[subscript 2]] and a positive correlation with [O[subscript 3]]. Co-measurements of temperature and NO[subscript 2] from the BT Tower were used to calculate the equilibrium partitioning between NO[subscript 3] and N[subscript 2]O[subscript 5] which was always found to strongly favour N[subscript 2]O[subscript 5] (NO[subscript 3]/N[subscript 2]O[subscript 5]=0.01 to 0.04). Two methods are used to calculate the lifetimes for NO[subscript 3] and N[subscript 2]O[subscript 5], the results being compared and discussed in terms of the implications for the night-time oxidation of nitrogen oxides and the night-time sinks for NO[subscript y]

Distribution of gaseous and particulate organic composition during dark ɑ-pinene ozonolysis

Secondary Organic Aerosol (SOA) affects atmospheric composition, air quality and radiative transfer, however major difficulties are encountered in the development of reliable models for SOA formation. Constraints on processes involved in SOA formation can be obtained by interpreting the speciation and evolution of organics in the gaseous and condensed phase simultaneously. In this study we investigate SOA formation from dark α-pinene ozonolysis with particular emphasis upon the mass distribution of gaseous and particulate organic species. A detailed model for SOA formation is compared with the results from experiments performed in the EUropean PHOtoREactor (EUPHORE) simulation chamber, including on-line gas-phase composition obtained from Chemical-Ionization-Reaction Time-Of-Flight Mass-Spectrometry measurements, and off-line analysis of SOA samples performed by Ion Trap Mass Spectrometry and Liquid Chromatography. The temporal profile of SOA mass concentration is relatively well reproduced by the model. Sensitivity analysis highlights the importance of the choice of vapour pressure estimation method, and the potential influence of condensed phase chemistry. Comparisons of the simulated gaseous- and condensed-phase mass distributions with those observed show a generally good agreement. The simulated speciation has been used to (i) propose a chemical structure for the principal gaseous semi-volatile organic compounds and condensed monomer organic species, (ii) provide evidence for the occurrence of recently suggested radical isomerisation channels not included in the basic model, and (iii) explore the possible contribution of a range of accretion reactions occurring in the condensed phase. We find that oligomer formation through esterification reactions gives the best agreement between the observed and simulated mass spectra

Measurements of iodine monoxide at a semi polluted coastal location

Point source measurements of IO by laser induced fluorescence spectroscopy were made at a semi-polluted coastal location during the Reactive Halogens in the Marine Boundary Layer (RHaMBLe) campaign in September 2006. The site, on the NW French coast in Roscoff, was characterised by extensive intertidal macroalgae beds which were exposed at low tide. The closest known iodine active macroalgae beds were at least 300m from the measurement point. From 20 days of measurements, IO was observed above the instrument limit of detection on 14 days, of which a clear diurnal profile was observed on 11 days. The maximum IO mixing ratio was 30.0 pptv (10 s integration period) during the day, amongst the highest concentrations ever observed in the atmosphere, and 1–2 pptv during the night. IO concentrations were strongly dependent on tidal height, the intensity of solar irradiation and meteorological conditions. An intercomparison of IO measurements made using point source and spatially averaged DOAS instruments confirms the presence of hot-spots of IO caused by an inhomogeneous distribution of macroalgae. The co-incident, point source measurement of IO and ultra fine particles (2.5 nm≥d≥10 nm) displayed a strong correlation, providing evidence that IO is involved in the production pathway of ultra fine particles at coastal locations. Finally, a modelling study shows that high IO concentrations which are likely to be produced in a macrolagae rich environment can significantly perturb the concentrations of OH and HO[subscript x] radicals. The effect of IO on HO[subscript x] is reduced as NO[subscript x] concentrations increase