We modified our 910-m long path THz system to increase the signal-to-noise ratio (S/N) with a nanostructure plasmonic THz transmitter (Tx) chip and a seven-mirror array reflector with 1 m diameter. When the THz pulse propagates the 910-m distance in the atmosphere, the S/N is up to 1170:1, which made the THz pulse measurable at a high water vapor density (WVD) of up to 25.2 g/m3. The time shift of the THz pulse according to the WVD measured for each meteorological season was matched well with the theoretical result. Due to the modified long-distance THz system, we were able to measure for the first time the resonances of N2O gas, which is located 455 m away from the Tx and receiver (Rx) chips and contained in a 1.5-m diameter rubber balloon under atmospheric pressure. Seven resonances can be detected except for one overlay of resonant frequency by water vapor.