diff --git a/src/ncar/obs2ioda/src/ncio_mod.f90 b/src/ncar/obs2ioda/src/ncio_mod.f90
index db6f54e02..2e3151ee8 100644
--- a/src/ncar/obs2ioda/src/ncio_mod.f90
+++ b/src/ncar/obs2ioda/src/ncio_mod.f90
@@ -148,15 +148,15 @@ subroutine write_obs (filedate, write_opt, outdir, itim, fileExt)
       status = netcdfAddVar(netcdfID, trim(ncname), NF90_INT, 1, [trim(ncname)])
 
       do i = 2, n_ncdim
-         status = netcdfAddDim(netcdfID, trim(name_ncdim(i)), val_ncdim(i), ncid_ncdim(i))
-         status = netcdfPutAtt(netcdfID, trim(name_ncdim(i)), val_ncdim(i))
-         status = netcdfAddVar(netcdfID, trim(name_ncdim(i)), NF90_INT, 1, [trim(name_ncdim(i))])
+         if ( (write_opt == write_nc_conv) .or. &
+           ((write_opt /= write_nc_conv) .and. (trim(name_ncdim(i)) /= 'nstring')) ) then
+            status = netcdfAddDim(netcdfID, trim(name_ncdim(i)), val_ncdim(i), ncid_ncdim(i))
+            status = netcdfPutAtt(netcdfID, trim(name_ncdim(i)), val_ncdim(i))
+            status = netcdfAddVar(netcdfID, trim(name_ncdim(i)), NF90_INT, 1, [trim(name_ncdim(i))])
+         end if
       end do
 
       ! define global attributes
-      status = netcdfPutAtt(netcdfID, "min_datetime", xdata(ityp, itim)%min_datetime)
-      status = netcdfPutAtt(netcdfID, "max_datetime", xdata(ityp, itim)%max_datetime)
-
       if ( allocated(xdata(ityp,itim)%wavenumber) ) then
          has_wavenumber = itrue
       else
diff --git a/test/testoutput/amsua_metop-b_obs_2020110112.nc4 b/test/testoutput/amsua_metop-b_obs_2020110112.nc4
index b4c7808d3..67dbf94af 100644
--- a/test/testoutput/amsua_metop-b_obs_2020110112.nc4
+++ b/test/testoutput/amsua_metop-b_obs_2020110112.nc4
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:218bc464a2fc77910c0694817a773d70bf1f283d2f64a159a63b7d63b9c38825
-size 80201
+oid sha256:d3c16a1cf6afbc8bcdffc99fa21381e9ee0807b014b17c97574ebecbe030b46b
+size 79603
diff --git a/test/testoutput/amsua_n18_obs_2020110112.nc4 b/test/testoutput/amsua_n18_obs_2020110112.nc4
index 22abeca6b..233b1db13 100644
--- a/test/testoutput/amsua_n18_obs_2020110112.nc4
+++ b/test/testoutput/amsua_n18_obs_2020110112.nc4
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:34ba505d99286afae2d3e073cd1c98a3abed83cfdc36ac5dab2f61d57165c6b3
-size 129269
+oid sha256:f4f9d437da9fa0597e3fcef1890cf168d6d2b6782a3e2b8548c7f47476948b39
+size 203243
diff --git a/test/testoutput/mhs_metop-b_obs_2020101215.nc4 b/test/testoutput/mhs_metop-b_obs_2020101215.nc4
index 5963c9154..77981b2d9 100644
--- a/test/testoutput/mhs_metop-b_obs_2020101215.nc4
+++ b/test/testoutput/mhs_metop-b_obs_2020101215.nc4
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:71531da1b96e1fc45cf752119946f1ce3fe12258be66a16b543759d7d21fb2ad
-size 2622121
+oid sha256:829ccf70af695493f9765574498e54ec6f41695b150ec36dd2114bdb47af3262
+size 530922
diff --git a/test/testoutput/sondes_obs_2020093018.nc4 b/test/testoutput/sondes_obs_2020093018.nc4
index 1c23f41e4..63ddf14c2 100644
--- a/test/testoutput/sondes_obs_2020093018.nc4
+++ b/test/testoutput/sondes_obs_2020093018.nc4
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:a6c99d0c4708d5b3c339cedf604db6981c167f49c9a19c445b6c5e1cd808d768
-size 498517
+oid sha256:12d1c49e8281d5edd7f331c9e2de180783a6bb94dfcf295f41c65429c0473bca
+size 498437