Analysis of new species retrieved from MIPAS

The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) instrument which operated on the Envisat satellite from 2002-2012 is a Fourier transform spectrometer for the measurement of high-resolution gaseous emission spectra at the Earth's limb. It operates in the nearto mid-infrared, where many of the main atmospheric trace gases have important emission features. The initial operational products were profiles of Temperature, H2O, O3, CH4, N2O, HNO3, and NO2, and this list was recently extended to include N2O5, ClONO2, CFC-11 and CFC-12. Here we present preliminary results of retrievals of the third set of species under consideration for inclusion in the operational processor: HCN, CF4, HCFC-22, COF2 and CCl4.


I. INTRODUCTION
he Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), which operated on the Envisat satellite from 2002-2012, is a Fourier transform spectrometer for the measurement of emission spectra at the Earth's limb.It operates in the near-to midinfrared where many of the main atmospheric trace gases have detectable emission features.The initial operational products were profiles of Temperature, H2O, O3, HNO3, CH4, N2O and NO2, and this list was recently extended to include N2O5, ClONO2,  In this paper the preliminary results of a third set of species, HCN, CFC-14 (CF4), HCFC-22, COF2, CCl4, SF6, OCS, HOCl and C2H6, retrieved using the Oxford L2 processor, MORSE (Multispectral Optimal Retrievals using Sequential Estimation), are presented.HCN, OCS and C2H6 are tracers of biomass burning (Rinsland et al., 1998;Li et al., 2000;Notholt et al., 2003;Logan et al., 1981).The relatively long lifetimes for HCN and C2H6 make them indicators of how transport redistributes pollutants on a global scale (Rinsland et al., 2005).CCl4, CFC-14, HCFC-22 and SF6 are mainly from anthropogenic emissions.For example CFC-14 are produced primarily as a byproduct during electrolytic aluminum production and SF6 is mainly from insulating electrical equipment.SF6 and CF4 are extremely longlived species and often used as tracers for the 'age of air'.HOCl is considered to be a reservoir for active chlorine, ClOx, and odd hydrogen, HOx, in the stratosphere (von Clarmann et al., 2012).It is produced primarily by the reaction of ClO and HO2 (peroxy radical) and is destroyed mainly by photo-dissociation, which returns OH and Cl radicals (Hickson et al., 2007).
Here we also examine fluorine species collectively measured by MIPAS.Stratospheric fluorine has important effects on the atmosphere, especially fluorine in long-lived greenhouse T gases.Over the past few decades, the major sources of fluorine in the stratosphere are the man-made chlorofluorocarbons CFCs and HCFCs.Photolysis of these compounds forms COF2.The COF2 molecule has been shown to be the second most abundant stratospheric fluorine reservoir (Kaye et al., 1991).

II. ZONAL MEAN DISTRIBUTIONS
The Oxford L2 processor MORSE has been used to retrieve these new species with the microwindows shown in Fig. 1.Here we analyze these new retrieved species to establish their zonal mean for the period of 2010 March.
For each gas, we eliminated those data that are cloud-affected and where a priori has a significant contribution, in other words, the retrieved random error greater than 50% of the volume mixing ratio (VMR).A 5σ global spike test is then applied to each species to eliminate unrealistic data.The percentage of profiles removed by the spike test is shown in Table 1.The largest percentage showed in the table is 21.5% from CFC-14.Reasons for these spike test failures have yet to be investigated.As the total number of profiles for each species for one month is over 32,000, there are still remaining a large number of profiles, over 25,000 profiles, to have a reliable sample basis for the further study.
The remaining profiles are used construct monthly zonal mean together with a standard deviation defined as the standard deviation of profiles contribute to each grid point, which is a combination of random error and atmosphere variability.Zonal plots of species CCl4, OCS, HCFC-22, SF6, C2H6 and COF2 in Fig. 2 show the expected structure for tropospheric source gases.The  with O(1D) in the upper stratosphere, which results in a decrease of VMR.
There are some unexpected features in the zonal plots for species CFC-14 and HCN.For example, a maximum VMR of HCN occurs near the stratopause over the equator, which seems unrealistic and requires comparison with other data sets.Similar for CFC-14 there is a maximum in the upper stratosphere over equator, which is unrealistic as well.Due to its complexity, HOCl species need further study before the data could be used for quantitative research.Figure 3 shows the vertical profiles of all the fluorine species and total fluorine (F) measured by MIPAS.In the lower stratosphere and upper troposphere, the atmospheric fluorine is mainly contributed by CFC-12.COF2 contributes nearly half of the fluorine VMR at 10hPa pressure level, while CFC-14 dominates in the upper stratosphere.The total [F] decreases with altitude as they are eventually formed into HF, which is not measured by MIPAS.The expected HF zonal plot for 2010 March is constructed by the following,

III. Total Fluorine
where [F] is the total fluorine zonal mean measured by MIPAS and [Fmax] is the maximum value of [F].This plot (Fig. 4) is further compared with the zonal plot of HF (fig.5) produced by Jones et al., 2012.

IV. CONCLUSIONS AND FUTURE WORK
Plausible distributions of HCFC-22, COF2, CCl4, SF6, OCS, HOCl and C2H6 retrieved by MIPAS, which CFC-14 and HCN have some anomalies requiring further investigation.However, further comparison with ACE-FTS, other MIPAS processor and model results are required for further justification.

Fig. 1 ,FigFig. 4 ,
Fig. 1, Microwindows for the new species.The upper panel shows the microwindows selected for these new species retrievals.The lower panel show the spectral signatures of these species.
Figure3shows the vertical profiles of all the fluorine species and total fluorine (F) measured by MIPAS.In the lower stratosphere and upper troposphere, the atmospheric fluorine is mainly contributed by CFC-12.COF2 contributes nearly half of the fluorine VMR at 10hPa pressure level, while CFC-14 dominates in the upper stratosphere.The total [F] decreases with altitude as they are eventually formed into HF, which is not measured by MIPAS.The expected HF zonal plot for 2010 March is constructed by the following,[HF] = [Fmax]-[F],where[F]  is the total fluorine zonal mean measured byMIPAS and [Fmax]  is the maximum value of [F].This plot (Fig.4) is further compared with the zonal plot of HF (fig.5)produced byJones et al., 2012.Fig 5 is a threemonth combined zonal average from ACE-FTS data during September-October-November.Fig4 and Fig 5 is for brief comparison of MIPAS data with ACE-FTS data of HF zonal means.

Fig. 3 ,
Fig. 3, The vertical profiles of all the fluorine containing species and the total fluorine retrieved by MIPAS.

Table 1 ,
percentage of removed profiles by 5σ spike test.