AC　breakdown　characteristics　of　nitrogen　at　different　pressures　in　electric　fields　with　different　degrees　of　non-uniformity　provided　by　a　sphere-plane　electrode　system　have　been　investigated.　It　is　found　that　the　measured　breakdown　voltages　obey　Paschen’s　law　at　the　values　of　the　field　factor　(the　ration　of　the　maximum　field　strength　between　electrodes　to　the　average　field　strength)　below　∼2.　Deviations　start　to　appear　and　increase　gradually　if　the　field　factor　increases　above　this　threshold.　Respectively,　the　dependence　of　the　breakdown　voltage　U　b　on　the　product　of　pressure　p　and　gap　distance　d　changes　from　been　linear　U　b　∼　p　×d　to　a　more　complex　relationship　of　type　U　b　∼　p　×ln(d).　It　is　found　that　the　maximum　field　strength　corresponding　to　the　breakdown　increases　with　increasing　gas　pressure　and　decreasing　electrode　radius　but　it　is　independent　on　the　gap　distance.　The　breakdown　voltages　predicted　by　the　streamer　criterion　agree　well　with　the　experimental　data.　The　results　obtained　for　nitrogen　were　compared　with　the　breakdown　characteristics　of　air　and　it　was　found　that　at　the　values　of　the　field　factor　below　9,　the　breakdown　strength　of　nitrogen　was　higher　than　that　of　ambient　air.　©　2023　IOP　Publishing　Ltd.