合肥市能见度与相对湿度、PM2.5质量浓度的定量关系

摘要

To understand the impacting factors of the visibility in Hefei, and provide scientific basis for the urban atmospheric visibility improvement, the hourly meteorological and environmental observations from January 2013 to December 2015 in Hefei city were used to investigate the relationships among atmospheric visibility, relative humidity (RH), and PM2.5 mass concentration. The statistical relationships between RH and PM2.5 were set up for different atmospheric visibility grades. It was found that atmospheric visibility in Hefei was jointly controlled by both RH and PM2.5. Under low RHconditions (RH<60%), the decrease in visibility was mainly ascribed to the increase of the PM2.5 mass concentration. High RH and PM2.5 mass concentration can significantly reduce the atmospheric visibility. Under high RH conditions (RH≥60%), due to the hygroscopic growth of the fine particulate can efficiently enhance light absorption and scattering, the visibility decreases more obvious in slight pollution. On average, the visibility was reduced by 0.172 km with 1% increment of RH when RH≥60%. When RH≥90%, the average visibilities were mostly less than 5 km. The best fitting relationship between the PM2.5 mass concentration and the visibility was a power function, and the effects of PM2.5on visibility were strongly significant when the RH is less than 60% but larger than or equal 40%. The PM2.5 mass concentration threshold that influences the atmospheric visibility decreases with increasing RH.Particularly, decreases in the PM2.5 mass concentration can lead to rapid increase in visibility when the PM2.5 mass concentration was less than 46μg·m-3. As the RH increases, or PM2.5 mass concentration increases, the frequency of low visibility rises. High RH and large PM2.5 mass concentration can significantly induce the occurring of lower atmospheric visibility. The factor of probability that visibility <5 km in a day was greater than 75%, when the visibility was below 7 km in its previous day and RH>75% with PM2.5>65μg·m-3 in the day. When the PM2.5 mass concentration reaches the moderately polluted level or above in its previous day, its visibility increases with RH decrease during this day, especially, the factor of probability that visibility <5 km in this day can reach 70% if RH reaches 80%.%为了研究合肥市能见度影响规律,为改善城市大气能见度提供科学依据,利用合肥市2013年1月—2015年12月的气象观测数据和颗粒物质量浓度数据,采用统计分析方法研究了合肥市大气能见度与相对湿度和PM2.5质量浓度的定量关系,以及不同等级能见度下相对湿度和PM2.5浓度的统计特征.结果表明,PM2.5质量浓度与相对湿度共同影响合肥市大气能见度变化,较低相对湿度下(RH<60%),能见度降低主要受PM2.5质量浓度升高的影响;较高湿度条件下(RH≥60%),能见度降低主要是由于相对湿度增加造成的大气粒子吸湿增长导致消光性能增大,且这种作用在污染程度较轻时更加突出.RH≥60%时,相对湿度每增加1%,平均能见度降低0.172 km;当RH≥90%时,平均能见度基本在5 km以下.PM2.5质量浓度与能见度呈幂函数关系,40%≤RH<60%时,PM2.5的影响作用最显著;PM2.5质量浓度对能见度的影响阈值随相对湿度增加而减小,当PM2.5质量浓度低于46μg·m-3时,能见度随着PM2.5质量浓度降低而迅速增大.随着相对湿度增加,或者PM2.5质量浓度增加,低能见度出现频率呈上升趋势;高湿度、高细颗粒物浓度均可导致低能见度的出现.当前一日能见度低于7 km,当日相对湿度大于75%,且PM2.5质量浓度大于65μg·m-3,当日能见度超过75%的比例在5 km以下.当前一日PM2.5质量浓度达到中度及以上污染,当日能见度随着相对湿度增加逐渐减小,RH≥80%时,能见度低于5 km的比例达到70%.