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利用2009年7月和12月的气象资料(风速、温度和相对湿度)、空气污染物(PM2.5、SO2、NOx和O3)和能见度的监测数据,探讨了西安市夏冬两个季节大气能见度变化特征及其影响因素.结果表明,西安夏季能见度平均值为11.12±5.78km变化范围在2.99~26.99km;冬季能见度明显低于夏季,其平均值为8.31±4.85km,变化范围2.56~18.08km.夏季早晨08时能见度最低为6.74km,下午18时最高为10.47km,而冬季下午14时能见度最高为8.10km:凌晨02时最低为5.13km.能见度与气象要素及空气污染物的相关分析结果表明,夏季温度、风速和相对湿度对能见度的影响不大,而冬季风速和相对湿度对能见度影响较大(相关系数分别为0.77和0.73).夏、冬季能见度与PM2.5、NOx和SO3均呈现较强的负相关,而O3对能见度的影响相对较小. “,”The meteorological observation data (wind speed, temperature and relative humidity ), air pollutants (PM2.5, SO2, NOx and O3 ) and the visibility of the monitoring data in July and December 2009 were obtained to investigate the characteristic of atmospheric visibility and its factors in Xi'an. The results showed that the visibility varied from 2.99 to 26.99 km with an average value of 11.12 ±5.78 km in summer. The visibility of winter was ranged from 2. 56 to 18. 08 km with an average value of 8.31 ± 4.85 km, which was obviously lower than in summer. In summer, the lowest average visibility was 6.74 km at 8:00 am, while the highest average visibility was 10.47 km at 18:00 pm. In contrast, the lowest mean visibility was 5. 12 km at 2:00 am in winter, and the highest mean visibility was 8.10 km at 14:00 pro. The correlation analysis showed that the temperature, wind speed and relative humidity had little correlation with visibility in summer, while the wind speed and relative humidity had good correlation with visibility in winter ( the correlation coefficients were 0.77 and 0.73, respectively). In summer and winter, the visibility had a strong negative correlation with PMz5, S02 and NOx, however, 03 had poor correlation with visibility.