Night-time chemistry above London: measurements of NO3 and N2O5 from the BT Tower

A. K. Benton, J. M. Langridge, S. M. Ball, W. J. Bloss, M. Dall'Osto, E. Nemitz, R. M. Harrison, R. L. Jones
2010 Atmospheric Chemistry and Physics  
Broadband cavity enhanced absorption spectroscopy (BBCEAS) has been used to measure the sum of concentrations of NO 3 and N 2 O 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 5 night-time nitrogen compounds: peak NO 3 +N 2 O 5 mixing ratios reached 800 pptv, whereas the mean night-time NO 3 +N 2 O 5 was approximately 30 pptv. Additionally, [NO 3 +N 2 O
more » ... 5 ] showed negative correlations with [NO] and [NO 2 ] and a positive correlation with [O 3 ]. Co-measurements of temperature and NO 2 from the BT Tower were used to calculate the equilibrium partitioning between NO 3 and N 2 O 5 which was al-10 ways found to strongly favour N 2 O 5 (NO 3 /N 2 O 5 =0.01 to 0.04). Two methods are used to calculate the lifetimes for NO 3 and N 2 O 5 , the results being compared and discussed in terms of the implications for the night-time oxidation of nitrogen oxides and the nighttime sinks for NO y . produced from thermal dissociation of N 2 O 5 . Mixing ratios of up to 800 pptv of N 2 O 5 were recently observed in Tokyo, Japan using one such technique (Matsumoto et al., Abstract 25 Fig. 4. LED-BBCEAS measurements of mixing ratios of NO 3 +N 2 O 5 (Panel (a) , red) from the REPARTEE-II campaign. All raw data (15s acquisitions) shown. A quantifiable measurement exists for all times where a LOD (Panel (a) , black) is shown. Data partitioned into N 2 O 5 (Panel (a) , blue) and NO 3 (Panel (c) , green) where required ancillary data (NO 2 and ambient temperature) is available. Panel (b) (grey) shows NO 3 /N 2 O 5 ratio in %. Fig. 8. Scatter plots showing correlation of mixing ratios of NO 3 +N 2 O 5 against (a) O 3 , (b) NO and (c) NO 2 for all night-time data.
doi:10.5194/acp-10-9781-2010 fatcat:u2ythe5bsfeida37g4kyjohnru