Atmospheric pressure air plasma discharges can generate abundance of biologically actives such as nitrogen oxides NOx (NO, NO2 etc) which are known as very important reactive oxygen and nitrogen species (RONS) in biomedical applications.[1-2] In this work, we focus on the study of NOx synthesis by nanosecond pin-plate discharge in atmospheric pressure air. The fourier transform infrared (FTIR) spectrum shows the primary species produced by this discharge only include NO, NO2, and HONO. The energy costs of NOx production decrease with increasing pulse width (in the range of 100ns to 260ns) from ~2400 GJ/tN (gigajoules per metric ton) to ~1000 GJ/tN. Detailed investigation of power consumption and NOx production throughout the pulse gives hints regarding the mechanisms of efficient NOx synthesis, namely that the initial and inefficient breakdown process is the main sink of energy. We show late-pulse, 2 mm gap NOx production energy cost may be as low as ~ 300 GJ/tN(~1.4 x 1017 molecules/J)which is something similar with gliding arc discharge results [3]. A simple 0D post-discharge kinetic model is able to reproduce the experimentally observed trends, assuming the main driver for NOx production is electronically excited nitrogen species N2,e*. The model implies an initial increasing trend for efficiency with increased N2,e* concentration which may explain the increase in efficiency we observe with increasing pulse width.