Seasonal variation of peroxyacetylnitrate (PAN) in coastal Antarctica measured with a new instrument for the detection of sub-part per trillion mixing ratios of PAN

Abstract

Abstract. An automated gas chromatograph with sample pre-concentration for the measurement of peroxyacetylnitrate (PAN) was constructed with a minimum detection limit below 1 pptv. This instrument was deployed at the British Antarctic Survey's Halley Research Station, Antarctica (75.6 • S, 26.6 • W) as part of the CHABLIS (Chemistry of the Antarctic Boundary Layer and the Interface with Snow) campaign. Hourly measurements were carried out between July 2004 and February 2005 with observed maximum and minimum mixing ratios of 52.3 and <0.6 pptv, respectively with a mean PAN mixing ratio for the measurement period of 9.2 pptv (standard deviation: 6.2 pptv). The changes in PAN mixing ratios typically occurred over periods of several days to a week and showed a strong similarity to the variation in alkenes. The mixing ratio of PAN at Halley has a possible seasonal cycle with a winter maximum and summer minimum, though the cycle is incomplete and the data are very variable. Calculations indicate that gross local PAN production is approximately 1 pptv d −1 in spring and 0.6 pptv d −1 in summer. Net loss of PAN transported to Halley in the summer is a small gas-phase source of NOx and net production of PAN in the spring is a very small NOx sink.

Interferences in photolytic NO&lt;sub&gt;2&lt;/sub&gt; measurements: explanation for an apparent missing oxidant?

“…It is therefore conservatively estimated that < 10 ppt NO 2 at 1000 ppt PAN (< 1 %) is produced by the PAN generator. This is less than previously estimated (Mills et al, 2007), albeit at higher PAN mixing ratios and lower residence times within the acetone photolysis cell with the same generator.…”

“…Next, the acetone photolysis lamp of the PAN generator was switched on so that acetone was photolysed in the presence of NO to form PAN. Complete NO conversion to PAN was indicated by the fact that in all cases the NO signal measured by the NO x analyser fell to ∼ 0 ppbv after the acetone-NO mixture was illuminated by the photolysis lamp; > 99.5 % conversion was reported by Mills et al (2007) with the same system. The diluent flow from the PAN generator was then varied to achieve PAN mixing ratios of between 0.2 and 1.3 ppbv.…”

“…In practice, an excess of acetone is used to ensure that NO reacts completely. A dedicated "PAN generator", as used by Whalley et al (2004), was employed to produce a consistent source of > 95 % pure PAN (Flocke et al, 2005;Mills et al, 2007). The generator consists of flow control elements for the NO standard gas, the acetone flow, and the zero-air diluent flow; a thermostatted (30 • C) acetone permeation oven consisting of a reservoir of HPLC grade acetone (ACS grade, Acros) with a silicone permeation tube placed in the headspace through which zero air flows; and a Pyrex glass photolysis cell illuminated by UV light centred at 285 nm (Pen-Ray mercury lamp, UVP).…”

“…The generator consists of flow control elements for the NO standard gas, the acetone flow, and the zero-air diluent flow; a thermostatted (30 • C) acetone permeation oven consisting of a reservoir of HPLC grade acetone (ACS grade, Acros) with a silicone permeation tube placed in the headspace through which zero air flows; and a Pyrex glass photolysis cell illuminated by UV light centred at 285 nm (Pen-Ray mercury lamp, UVP). The Pyrex functions to filter wavelengths below 290 nm within the photolysis cell, thus minimizing PAN photolysis (Mills et al, 2007).…”

“…A minor product also found in the photolysis of acetone is methyl nitrate, MeONO 2 , which is typically approximately 1 % of the total yield (Mills et al, 2007). The proposed origin of the methyl nitrate (Williams et al, 2014) is shown in Reaction (R14) and formaldehyde, which is formed as a major by-product is shown in Reaction (R15) (Singh et al, 1995: Warneck andZerbach, 1992).…”