Two questions to aid us in our response:
1. Are you seeking Level 2 swath data or Level 3 global gridded data?
2. If L3, do you want to subset for a region or acquire the full global file?
Because you asked about NO2_1 and not NO2d_1, I would assume you are seeking Level 2, but for efficiency I want to make sure.
I will forward your question to our scientific staff. While waiting for their response, I recommend examining this How-To document to determine if will assist your efforts:
https://disc.sci.gsfc.nasa.gov/informat ... GPM_2ADPR
To assist you further, our data specialist would like to know if you are interested in grid sizes other than 0.25 degree, and what temporal period you are investigating.