# Why the dataset "CAMS global greenhouse gas reanalysis (EGG4) monthly averaged fields" don't caculate the Carbon dioxide total column dry mole fraction? **URL:** \ **Category:** CAMS - Datasets and Usage\ **Tags:** cams, ghg, egg4\ **Created:** [14 September 2021 02:44 UTC](https://forum.ecmwf.int/t/why-the-dataset-cams-global-greenhouse-gas-reanalysis-egg4-monthly-averaged-fields-dont-caculate-the-carbon-dioxide-total-column-dry-mole-fraction/1356 "2021-09-14T02:44:00Z")\ **Posts on this page:** 1\ **Page:** 1
**Author:** ![Mitch\_John](https://forum.ecmwf.int/letter_avatar_proxy/v4/letter/m/8edcca/32.png) [@Mitch\_John](https://forum.ecmwf.int/u/Mitch_John)\ **Post date:** [14 September 2021 02:44 UTC](https://forum.ecmwf.int/t/why-the-dataset-cams-global-greenhouse-gas-reanalysis-egg4-monthly-averaged-fields-dont-caculate-the-carbon-dioxide-total-column-dry-mole-fraction/1356/1 "2021-09-14T02:44:00Z")
Hi everyone,      The CAMS dataset in the website [https://ads.atmosphere.copernicus.eu/cdsapp#!/search?type=dataset](https://ads.atmosphere.copernicus.eu/cdsapp#!/search?type=dataset) provide some gresshouse dataset,which is very useful for global climate research. However,in this website provide two dataset for it. The one is "**CAMS global greenhouse gas reanalysis (EGG4) monthly averaged fields**"  with  spatial resolution 0.75°x0.75° ，and the another is " **CAMS global inversion-optimised greenhouse gas fluxes and concentrations" ** with spatial resolution 1.9° x 3.75°. So what is the difference between them? And for the carbon dioxide,why  does the second data caculate the Carbon dioxide total column dry mole fraction, but the first one don't, just  CO2 column-mean molar fraction? What's the difference by considering dry air? How to caculate CO2 total column in dir air  from the 0.75°x0.75° dataset? Thanks. Sorry for my  basic questions, but I a beginner of  atmspheric chemistry.  Looking forward to reply.  Sincerely, Mitch John