Peroxyacetyl nitrate (PAN) and peroxyacetic acid (PAA) measurements by iodide chemical ionisation mass spectrometry: first analysis of results in the boreal forest and implications for the measurement of PAN fluxes

Abstract

We describe measurements of peroxyacetyl nitrate (CH<sub>3</sub>C(O)O<sub>2</sub>NO<sub>2</sub>, PAN) and peroxyacetic acid (CH<sub>3</sub>C(O)OOH, PAA) in the Boreal forest using iodide chemical ionization mass spectrometry (ICIMS). The measurements were made during the Hyytiälä United Measurement of Photochemistry and Particles – Comprehensive Organic Particle and Environmental Chemistry (HUMPPA-COPEC-2010) measurement intensive. Mixing ratios of PAN and PAA were determined by measuring the acetate ion signal (CH<sub>3</sub>C(O)O<sup>−</sup>, <i>m/z</i> = 59) resulting from reaction of CH<sub>3</sub>C(O)O<sub>2</sub> (from the thermal dissociation of PAN) or CH<sub>3</sub>C(O)OOH with iodide ions using alternatively heated and ambient temperature inlet lines. During some periods of high temperature (~ 30 °C) and low NO<sub>x</sub> (< 1 ppbv), PAA mixing ratios were similar to, or exceeded those of PAN and thus contributed a significant fraction of the total acetate signal. PAA is thus a potential interference for ICIMS measurements of PAN, and especially eddy covariance flux measurements in environments where the PAA flux is likely to be a significant proportion of the (short timescale) acetate ion variability. Within the range of mixing ratios of NO<sub>x</sub> measured during HUMPPA-COPEC, the modelled ratio of PAA-to-PAN was found to be sensitive to temperature (through the thermal decomposition rate of PAN) and the HO<sub>2</sub> mixing ratio, thus providing some constraint to estimates of photochemical activity and oxidation rates in the Boreal environment

Estimating N<sub>2</sub>O<sub>5</sub> uptake coefficients using ambient measurements of NO<sub>3</sub>, N<sub>2</sub>O<sub>5</sub>, ClNO<sub>2</sub> and particle-phase nitrate

“…The atmosphere was sampled by drawing air at ∼ 20 SLM through a 3/8 inch (∼ 9.5 mm) outer-diameter PFA tube 8 m in length and sub sampling approximately 4 SLM into the cavity. The main inlet was shared by the iodide CIMS system which was used to measure ClNO 2 , speciated peroxy nitrates and peroxy acids (Phillips et al, 2012(Phillips et al, , 2013b.…”

Direct measurements of OH and other product yields from the HO<sub>2</sub> + CH<sub>3</sub>C(O)O<sub>2</sub> reaction

“…This process is a radical sink in the atmosphere, as a fraction of the water soluble peroxide is lost before radicals are regenerated by photolysis. Observations of ROOH are important as they can be used as an indication of the oxidative capacity of the troposphere (Phillips et al, 2013) and uptake onto aqueous aerosol may influence S(IV) to S(VI) conversion (Lee et al, 2000).…”

Development of a photochemical source for the production and calibration of acyl peroxynitrate compounds

“…An increasingly popular method is thermal-dissociation chemical ionization mass spectrometry (TD-CIMS) for the measurement of APNs (Slusher et al, 2004;Phillips et al, 2013;Zheng et al, 2011). Comparisons of the TD-CIMS method with other techniques, such as GC and TD-LIF, show reasonably good agreement (Wooldridge et al, 2010;Tyndall et al, 2005).…”

“…The most atmospherically abundant and well-understood of the APNs is acetyl peroxynitrate (PAN, CH 3 C(O)O 2 NO 2 ) formed from the oxidation of VOCs (Roberts, 2007;Fischer et al, 2014;Singh et al, 1992;LaFranchi et al, 2009;Moxim et al, 1996;Phillips et al, 2013;Roberts et al, 2004Roberts et al, , 2007Williams et al, 1997). Recent research has become increasingly focused on less-well-studied APNs due to their involvement in several key atmospheric processes.…”

“…Comparisons of the TD-CIMS method with other techniques, such as GC and TD-LIF, show reasonably good agreement (Wooldridge et al, 2010;Tyndall et al, 2005). However, there exists the potential for various interferences, such as peroxy acetic acid and carboxylic acids, requiring additional consideration (Phillips et al, 2013).…”