Satellite observations of peroxyacetyl nitrate from the Aura Tropospheric Emission Spectrometer

V H Payne,J R Worden,M J Alvarado,E V Fischer,K E Cady-Pereira,S S Kulawik

doi:10.5194/amt-7-3737-2014

Abstract

Abstract. We present a description of the algorithm used to retrieve peroxyacetyl nitrate (PAN) concentrations from the Aura Tropospheric Emission Spectrometer (TES). We describe the spectral microwindows, error analysis, and the utilization of a priori and initial guess information provided by the GEOS-Chem global chemical transport model. The TES PAN retrievals contain up to one degree of freedom for signal. In general, the retrievals are most sensitive to PAN in the mid-troposphere. Estimated single-measurement uncertainties are on the order of 30 to 50%. The detection limit for a single TES measurement is dependent on the atmospheric and surface conditions as well as on the instrument noise. For observations where the cloud optical depth is less than 0.5, we find that the TES detection limit for PAN is in the region of 200 to 300 pptv. We show that PAN retrievals capture plumes associated with boreal burning. Retrievals over the Northern Hemisphere Pacific in springtime show spatial features that are qualitatively consistent with the expected distribution of PAN in outflow of Asian pollution.

Highlights

Peroxyacetyl nitrate (PAN) is a thermally unstable reservoir for active nitrogen (NOx) that allows for NOx to be transported over large distances, enabling efficient ozone formation far downwind from the original source (Singh and Hanst,1981; Hudman et al, 2004; Fischer et al, 2010; Singh, 1987)
Building on the detection of PAN in Tropospheric Emission Spectrometer (TES) radiances described by Alvarado et al (2011), we have developed a PAN retrieval product for TES
Due to the nature of the broad PAN spectral feature, or perhaps the relatively coarse spectral resolution of the PAN cross-section data used in the forward model, we found that the retrieval did not attempt to obtain better fits by introducing oscillations in the profile, and we did not find it necessary to introduce off-diagonal elements in the constraint matrix

Summary

Introduction

Peroxyacetyl nitrate (PAN) is a thermally unstable reservoir for active nitrogen (NOx) that allows for NOx to be transported over large distances, enabling efficient ozone formation far downwind from the original source (Singh and Hanst,1981; Hudman et al, 2004; Fischer et al, 2010; Singh, 1987). PAN signatures have been observed in nadir observations of smoke plumes from fires by both the Aura Tropospheric Emission Spectrometer (TES) (Alvarado et al.2,7 2011) and MetOp-A Infrared Atmospheric Sounding Instrument (IASI) (Clarisse et al, 2011), but, to our knowledge, PAN has not previously been retrieved in the nadir view on a global scale. The 1730 and 1840 cm−1 PAN absorption bands are outside the spectral ranges measured by TES These bands, covered by other spaceborne thermal infrared instruments, are very strongly impacted by water vapor interference, which would complicate their use in retrievals

Forward model

Retrieval approach

A priori constraints

Error estimates

Example retrieval results

Summary and conclusions