Recent studies on the air pollution Environmental Kuznets Curve (EKC) in South Korea imply an N-shaped curve, suggesting the worsening of air pollution in the country. This study aims to test the EKC hypothesis of South Korea by considering China’s transboundary air pollution effect. We estimate EKC for monthly PM10 with the generalized least squares approach using meteorological and economic factors, and China’s effect during 2000–2021. We find that PM10 pollution shows an N-shaped trajectory EKC with turning points at $6,836 and $12,662, suggesting that China’s effect may have played a role in the process of improving and deteriorating air quality in South Korea. We also confirm that major air pollutants (PM10, SO2, and NO2) are cointegrated using the seemingly unrelated regressions (SUR) model. The findings suggest a need for regional cooperation, taking into account the transboundary effects from neighboring countries to mitigate air pollution in a country.