Abstract
This work presents 15-min averaged measurements of peroxyacetyl nitrate (PAN) obtained during spring 2014 (24/04/2014 – 06/05/2014) at the Auchencorth UK EMEP supersite (southeast Scotland). The aim of this analysis was to investigate the conditions producing the distribution of PAN mixing ratios at the supersite in spring 2014. Air mass back trajectories showed the majority of air masses to have spent substantial time over the UK, continental Europe or Scandinavia prior to arrival at Auchencorth. The median and 95th percentile PAN mixing ratios observed were 0.46ppb and 1.03ppb, respectively. The median mixing ratio was elevated compared with previous PAN measurements during springtime (April–May) in southeast Scotland (corresponding median mixing ratios April–May 1994–1998: 0.1–0.3ppb), which is hypothesised to be due to conditions conducive to regional (European) photochemical PAN production. Additionally, PAN mixing ratios during regionally influenced conditions (0.4–1.5ppb) were substantially more elevated from hemispheric background mixing ratios (0.4–0.6ppb) than for ozone (O3, regional: 10–45ppb, hemispheric: 30–40ppb). PAN and O3 both impact upon vegetation and human health and it is necessary to understand the extent to which hemispheric and regional processes contribute to their abundances in different locations. Regional processes can both increase and decrease PAN and O3 mixing ratios compared to imported hemispheric background mixing ratios. This study concludes that during the measurement period in spring 2014 at the Auchencorth supersite, regional PAN and O3 modifying processes enhanced PAN mixing ratios more than for O3.
Highlights
Peroxyacetyl nitrate (PAN) is a secondary pollutant formed photochemically in aging air masses from the OH-initiated degradation of hydrocarbons, and combination with nitrogen dioxide (NO2)
peroxyacetyl nitrate (PAN) plays an important role in determining the spatial distribution of ozone (O3) across the globe (Fischer et al, 2014)
The major variations in PAN mixing ratios across the measurement period are associated with changes in air mass origin, represented by 96-h back trajectories
Summary
Peroxyacetyl nitrate (PAN) is a secondary pollutant formed photochemically in aging air masses from the OH-initiated degradation of hydrocarbons, and combination with nitrogen dioxide (NO2). The reaction of PA with NO2 forms PAN (R2) (Seinfeld and Pandis, 2006). This reaction is reversible and PAN can thermally decompose back to PA and NO2, which can result in a PAN sink through the reaction of PA with NO (R3). PAN plays an important role in determining the spatial distribution of ozone (O3) across the globe (Fischer et al, 2014). PAN has been shown to be a constituent of surface air in a variety of locations, including urban (Grosjean, 2001), rural
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