An airborne study of air quality was made around the Hong Kong Territory during October and November of 1994. The air quality measurements included NO, NOy, O3, CO, SO2, condensation nuclei, black carbon, aerosol light scattering, and aerosol particle size and number. Complex wind patterns are present, mixing the emissions from Hong Kong with aged pollution transported into the region from the People's Republic of China. This leads to poor air quality on the west and north sides of the Hong Kong Territory. CO mixing ratios were 200--800 parts per billion by volume (ppbv), and black carbon was present in the range of 5--7 μg/m3. Ozone mixing ratios of 100--120 ppbv were typical. The CO/NOy ratio in the heavily polluted region was 10, similar to the CO/NOy emission ratio for pollution emitted from the People's Republic of China immediately upwind of Hong Kong.¿ 1997 American Geophysical Union