On the other hand , the environmental protection department published the " practice note for managing air quality in air - conditioned public transport facilities " in november 2003 . the practice note sets the air quality objectives for such facilities and provides that the railway corporations should monitor one - hour average concentration of carbon dioxide during normal operations at peak hours at least once a year 另一方面，环境保护署在二三年十一月公布管理空调公共运输设施内空气质素专业守则，就有关设施制订空气质素指标，以及订明铁路公司应至少每年一次，在繁忙时间及正常运作的情况下，监测铁路设施的二氧化碳平均每小时的浓度。
The reason for this approach was in recognition of the fact that changes in different sectors ( eg transport , waste management , industry etc ) may be picked up using cross - sectoral indicators ( eg air quality indicators , gdp or income differential ) rather than developing less flexible sector - specific indicators 采纳这个方法的原因，是某项政策或计划对不同范畴（例如，运输、废物处理、工业等）所带来的改变，可利用涵盖范围较广的指标（例如，空气质素指标、本地生产总值或贫富差距）反映出来，故无须拟订弹性较低、只适用于特定范畴的指标。
