When a temperature inversion is formed in the pearl river delta ( prd ) region , or when a weak northerly or northwesterly wind prevails , ambient air pollutants ( including nox and voc ) in the region will be trapped easily in the lower atmosphere and cannot be dispersed effectively . the above factors , if coupled with strong sunlight , will favour the building up of ozone concentrations 当珠江三角洲区域一带出现逆温层现象，或者吹微弱北或西北风时，区域内空气中的污染物（包括氮氧化物及挥发性有机化合物）很容易会被困在大气的低层，不能有效消散；如再加上强烈的阳光，臭氧浓度便会增高。
When a temperature inversion is formed in the pearl river delta ( prd ) region , or when a weak northerly or northwesterly wind prevails , ambient air pollutants ( including nitrogen oxides ( nox ) and volatile organic compounds ( voc ) ) in the region will be trapped easily in the lower atmosphere and cannot be dispersed effectively . the above factors , if coupled with strong sunlight , will generate ozone under photochemical reaction between nox and voc and lead to the phenomenon of photochemical smog 当珠江三角洲区域一带出现逆温层，或者吹微弱北或西北风时，区域内空气中的污染物（包括氮氧化物及挥发性有机化合物）很容易会被困在大气的低层，不能有效消散；如再加上强烈的阳光，氮氧化物与挥发性有机化合物便会产生光合化学反应，形成臭氧及引致光合化学烟雾现象。
