KUCHING, Sept 5 — Air quality in Serian improved slightly, with its Air Pollutant Index (API) reading dropping to 390 by 7am today from 498, which was categorised as very hazardous at 8pm yesterday.According to the Natural Resources Environment Board’s Air Pollutant Index (API) Status for Sarawak, Kuching’s API reading also fell to 277 by 7am from 298 at 8pm, but remained at a very unhealthy level.Other locations that recorded very unhealthy air…