(with thanks to Michail Diamantakis)

For global mass conservation of air the following settings should be added in namelists:

&NAMDYN
LMASCOR=true,
LMASDRY=true,

(the above fixes the dry air mass only and leaves the fluctuation in the total mass due to moist parametrizations - annual water cycle)
The above turn on the spectral mass fixer.

&NAMCT0
NFRMASSCON=1,

 (the above specifies that the mass fixer will be applied every step)

&NAMGFL
YS_NL%LMASSFIX=true,
YR_NL%LMASSFIX=true,
YI_NL%LMASSFIX=true,
YL_NL%LMASSFIX=true,
YQ_NL%LMASSFIX=true,
LTRCMFIX=true,

the above activates and controls the tracer mass fixer. It applies it on spec humidity, cloud water, cloud ice, cloud rain, cloud snow: YQ_NL, YL_NL, YI_NL, YR_NL, YS_NL IFS variables respectively.

An additional small code modification is needed in

ifs/control/tracmf.F90

Uncomment lines 112, 113, 114, 115,

112		!LTRCMFP=.TRUE.  ! proportional 
113		!LTRCMFA_LAP=.FALSE.  ! additive based on hor. Laplace
114		!LTRCMFA_VER=.FALSE.  ! additive based on vert. Lapace
115		!LTRCMFA_DIF=.FALSE.   ! additiva based on abs gradient

  Lot more work has been done on mass fixers at later versions.

<script type="text/javascript" src="https://software.ecmwf.int/issues/s/en_UKet2vtj/787/12/1.2.5/_/download/batch/com.atlassian.jira.collector.plugin.jira-issue-collector-plugin:issuecollector/com.atlassian.jira.collector.plugin.jira-issue-collector-plugin:issuecollector.js?collectorId=5fd84ec6"></script>