Satellite measurements have revealed that the Indo-Gangetic Plain (IGP) has the global maximum ammonia concentrations, with a peak from June to August. Here, we studied the reasons for this phenomenon through computer simulations. Low sulfur dioxide and nitrogen oxides emissions and high air temperature over the IGP weaken the swallowing of gaseous ammonia by acidic gases. Additionally, the barrier effects of the Himalayas, like a windshield, are also conducive to the accumulation of ammonia.