Abstract
In this study, we present simultaneous airborne measurements of peroxyacetyl nitrate (PAN), ethane (C2H6), formic acid (HCOOH), methanol (CH3OH), and ethylene (C2H4) above the South Atlantic in September and October 2019. Observations were obtained from the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA), as two-dimensional altitude cross-sections along the flight path. The flights were part of the SouthTRAC (Transport and Composition in the Southern Hemisphere Upper Troposphere/Lower Stratosphere) campaign with the German High Altitude and Long range research Aircraft (HALO). On two flights (8 September 2019 and 7 October 2019), large enhancements of all these substances were found between 7 and 14 km altitude with maximum volume mixing ratios (VMRs) of 1000 pptv of PAN, 1400 pptv for C2H6, 800 pptv for HCOOH, 4500 pptv for CH3OH, and 200 pptv for C2H4. One flight shows a common filamentary structure in the trace gas distributions, while the second flight is characterized by one large plume. Using backward trajectories, we show that measured pollutants are likely originating from South America and central Africa, where elevated PAN VMRs are visible at the surface layer of the Copernicus Atmosphere Monitoring Service (CAMS) model during the weeks before both measurements. In comparison to simulation results of the CAMS reanalysis interpolated onto the GLORIA measurement geolocations, we show that the model is able to reproduce the overall structure of the measured pollution trace gas distributions. For PAN, the absolute VMRs are in agreement with the GLORIA measurements, too. However, C2H6 and HCOOH are generally underestimated by the model, while CH3OH and C2H4, the species with the shortest atmospheric lifetimes of the discussed pollution trace gases, are overestimated by CAMS. The good agreement between model and observations for PAN suggests that the general transport pathways and emissions locations are well captured by the model. The poorer agreement for other species is therefore most likely linked to model deficiencies in the representation of loss processes and emission strength.
Highlights
This study discusses simultaneous airborne measurements of peroxyacetyl nitrate (PAN), C2H6, HCOOH, CH3OH, and C2H4 measured by GLORIA 295 during the SouthTRAC campaign in September and October 2019
While the flight on 8 September 2019 revealed a filamentary structure of pollution trace gas enhancements, the flight on 7 October 2019 was characterized by a large plume with high absolute volume mixing ratios (VMRs) of all discussed trace gases but C2H4
310 The comparison of the GLORIA cross sections with interpolated Copernicus Atmosphere Monitoring Service (CAMS) reanalysis data illustrates the strength of the CAMS model to reproduce measured PAN VMR distributions
Summary
Peroxyacetyl nitrate (PAN), ethane (C2H6), formic acid (HCOOH), methanol (CH3OH), and ethylene (C2H4) are discussed, and their characteristics are summarized in Tab. 1 These trace gases have been observed by several satellite instruments in nadir (e.g., Coheur et al, 2009; Dolan et al, 2016; Franco et al, 2018; Pope et al, 2021) as well as in limb views (e.g., Rinsland et al, 2005; Dufour et al, 2007; Grutter et al, 2010; Wiegele et al, 2012). Airborne in situ 35 (e.g., Singh et al, 2001; Peischl et al, 2018) and remote sensing (e.g., Ungermann et al, 2013; Johansson et al, 2020; Wetzel et al, 2021) observations provided detailed studies of filamentary structures of these pollution trace gases Atmospheric simulations of such pollution trace gases are challenging: Biomass burning events are typically represented by emission data sets in atmospheric models. Sources Precursors: Fuel combustion Biomass burning Biomass burning Natural gas loss Fossil fuel production Bio fuel use Biogenic emissions Biomass burning Fossil fuel combustion Secondary production Biogenic emissions Oceanic emissions Biomass burning Anthropogenic emissions Secondary production Biogenic emissions Biomass burning Fossil fuel combustion
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