Analysis of space-based observations of peroxyacetyl nitrate (PAN) and its relation to other atmospheric tracers

<p>Peroxyacetyl nitrate (CH<sub>3</sub>C(O)O<sub>2</sub>NO<sub>2</sub>; abbreviated as PAN) is the main tropospheric reservoir of nitrogen oxide radicals (NO<sub>x</sub>) and contributes to redistributing NO<sub>x</sub> from source to remote regions. Recently, PAN total columns have been retrieved from the radiance spectra recorded by IASI (Infrared Atmospheric Sounding Interferometer) onboard the Metop satellite platforms, using a neural network-based retrieval approach. The daily global distributions obtained from these measurements provide a comprehensive picture of PAN through the troposphere.</p><p>Here we exploit as a climatology the 13-year time series of global PAN measurements derived from the IASI/Metop-A observations (October 2007 - December 2020) to characterize the spatial distribution and seasonal variability of PAN abundance worldwide. In particular, continental areas within the tropics appear to be source regions of PAN throughout the year, whereas PAN at North Hemisphere mid- and high latitudes exhibits a more pronounced seasonal cycle and peaks during the boreal summer. Strong outflows of PAN are captured over the oceans, downwind of continental source regions such as Eastern Asia and Eastern US. This dataset also allows us to investigate the recent trends of atmospheric PAN abundance over the last 13 years, over both source and remote areas.</p><p>To better understand what drives the spatial distribution and variability of PAN, we analyze alongside the regional time series of PAN those of carbon monoxide (CO) from IASI/Metop-A, and of formaldehyde (HCHO) and nitrogen dioxide (NO<sub>2</sub>) from OMI/Aura (Ozone Monitoring Instrument). Locally, we find simultaneous enhancements of PAN and CO abundances, which in this case indicates that most PAN originates from fire-derived precursors. This mainly occurs over the typical biomass burning regions in the tropics. Overall, strong correlations are observed over source areas between PAN and HCHO, which is used here as a tracer of tropospheric chemistry and of the presence of oxygenated volatile organic compounds (OVOCs), while there is no particular correlation with NO<sub>2</sub>. The preliminary results suggest that PAN distribution and seasonality is primarily driven by the availability in OVOCs, and hence in peroxyacetyl radical, and that a locally weak NO<sub>2</sub> abundance does not prevent the formation of PAN.</p>

Retrieval of Ozone Total Columns over Evora-Portugal Using Remote Sensing Instruments During 2007-2011

The present study deals with the retrieval of Ozone (O3) Total Column (TOC) and analysis of its variability over the Observatory of the Geophysics Centre of Évora (CGE-UE) –Portugal (38.5ºN; 7.9 ºW, 300 m a.s.l.) for the period comprised 2007-2011. The data presented in this study are obtained applying the Differential Optical Absorption Spectroscopy (DOAS) methodology to the measurements of diffused spectral sky radiation carried out along the zenith direction performed with the multipurpose UV-Vis. Spectrometer for Atmospheric Tracers Monitoring (SPATRAM) in the 250-900 nm spectral range. This ground-based spectrometer is installed at CGE-UE performing daily and automatic measurements since 2004. Other products of this scanning spectrometer are the vertical profiles of some trace gases (e.g. NO2) and monitoring of air quality. The O3 retrieved with the SPATRAM instrument confirm the typical seasonal cycle for middle latitudes reaching the maximum during the spring and the minimum during the autumn. The ground-based results obtained for O3 column are also compared with data from SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) and Global Ozone Monitoring Experiment (GOME) instruments aboard ENVISAT and ERS-2 satellites, respectively. The results show a good agreement between the datasets. The main reasons for the observed differences are discussed.

Global mass fixer algorithms for conservative tracer transport in the ECMWF model

Various mass fixer algorithms (MFAs) have been implemented in the Integrated Forecasting System (IFS) of the European Centre for Medium-Range Weather Forecasts (ECMWF) to ensure mass conservation of atmospheric tracers within the semi-Lagrangian (SL) advection scheme. Emphasis has been placed in implementing schemes that despite being primarily global in nature adjust the solution mostly in regions where the advected field has large gradients and therefore interpolation (transport) error is assumed larger. The MFAs have been tested in weather forecast, idealised and atmospheric dispersion cases. Applying these fixers to specific humidity and cloud fields did not change the accuracy of 10-day forecasts. In other words, global mass tracer conservation is achieved without deteriorating the solution accuracy. However, for longer forecast timescales or for forecasts in which correlated species are transported, experiments suggest that MFAs may improve IFS forecasts.

Global mass fixer algorithms for conservative tracer transport in the ECMWF model

Various mass fixer algorithms (MFA) have been implemented in the Integrated Forecasting System (IFS) of ECMWF to ensure mass conservation of atmospheric tracers within the Semi-Lagrangian (SL) advection scheme. Emphasis has been placed in implementing schemes that despite being primarily global in nature adjust the solution mostly in regions where the advected field has large gradients and therefore interpolation (transport) error is assumed larger. The MFA have been tested in weather forecast, idealised and atmospheric dispersion cases. Applying these fixers to specific humidity and cloud fields did not change the accuracy of 10 day forecasts. In other words, global mass tracer conservation is achieved without deteriorating the solution accuracy. However, for longer forecast timescales or for forecasts in which correlated species are transported, experiments suggest that MFA may improve IFS forecasts.