Closing the peroxy acetyl nitrate budget: observations of acyl peroxy nitrates (PAN, PPN, and MPAN) during BEARPEX 2007

Abstract

Abstract. Acyl peroxy nitrates (APNs, also known as PANs) are formed from the oxidation of aldehydes and other oxygenated VOC (oVOC) in the presence of NO 2 . There are both anthropogenic and biogenic oVOC precursors to APNs, but a detailed evaluation of this chemistry against observations has proven elusive. Here we describe measurements of PAN, PPN, and MPAN along with the majority of chemicals that participate in their production and loss, including OH, HO 2 , numerous oVOC, and NO 2 . Observations were made during the Biosphere Effects on AeRosols and Photochemistry Experiment (BEARPEX 2007) in the outflow of the Sacramento urban plume. These observations are used to evaluate a detailed chemical model of APN ratios and concentrations. We find that the ratios of APNs are nearly independent of the loss mechanisms and thus an especially good test of our understanding of their sources. We show that oxidation of methylvinyl ketone, methacrolein, methyl glyoxal, biacetyl and acetaldehyde are all significant sources of the PAN+peroxy acetyl (PA) radical reservoir, accounting for 26%, 2%, 7%, 20%, and 45%, of the production rate on Correspondence to: J. A. Thornton (thornton@atmos.washington.edu) average during the campaign, respectively. At high temperatures, when upwind isoprene emissions are highest, oxidation of non-acetaldehyde PA radical sources contributes over 60% to the total PA production rate, with methylvinyl ketone being the most important of the isoprene-derived sources. An analysis of absolute APN concentrations reveals a missing APN sink that can be resolved by increasing the PA+ RO 2 rate constant by a factor of 3.

On the temperature dependence of organic reactivity, nitrogen oxides, ozone production, and the impact of emission controls in San Joaquin Valley, California

“…This is the same ratio of MVK to methacrolein observed during BEARPEX-2007(LaFranchi et al, 2009). We do not include an estimate for second-generation isoprene oxidation products.…”

“…Methacrolein, biacetyl, MVK, and methyl glyoxal are also known PAN sources. Biacetyl, MVK, and methyl glyoxal were not measured during CalNex-SJV, so to test this second assumption, we approximated their concentrations via ratios to methacrolein, as observed during the Biosphere Effects on AeRosol and Photochemistry Experiment (BEARPEX) (LaFranchi et al, 2009), which took place 15 June-31 July 2007 at a site located ∼3 h downwind from an isoprene source region. Using the calculated acetaldehyde (Fig.…”

Observational Insights into Aerosol Formation from Isoprene

“…Under cooler conditions (<15°C), MPAN thermal decomposition is much slower compared to the reformation reaction of the PMA radical with NO 2 and in this situation the reaction with OH can compete with thermal decomposition as a loss pathway for Figures S6 and S7, Supporting Information). To investigate the role the MPAN thermal lifetime has on limiting SOA formation from the OH oxidation of MPAN, we employed a steady state model of acyl peroxy nitrates (APN model) as described in previous work by LaFranchi et al, 52 constrained by measurements made during both BEARPEX campaigns. Figure 3a shows the relationship between the observed ambient temperature, measurements of the HO 2 /OH ratio, and the ratio of MPAN loss to reaction with OH (the SOA formation pathway) to the MPA loss to reaction with NO, HO 2 , and RO 2 (F MAE formation ) determined from the APN model.…”

The production and persistence of ΣRONO&lt;sub&gt;2&lt;/sub&gt; in the Mexico City plume

“…Photochemical age indicators depend on the assumption that parent and daughter molecules, in this case a particular straight-chain alkane and its daughter alkyl nitrate arise exclusively from a single chemical reaction (or a chain with a well-defined rate limiting step) and that the loss processes of the daughter are slower than the parent and well known. In addition, this analysis assumes that the emissions are effectively from a single isolated point source (LaFranchi et al, 2009). Depending on the accuracy required, mixing of a background into the plume must also be taken into account (Day et al, 2003).…”