Characteristics And Origins Of Haze Pollution Studied With Observations And 3-D Air Quality Model

In recent years,haze pollution occurred in China frequently,especially in the Beijing-Tianjin-Hebei region,the Yangtze River Delta area,and the Pearl River Delta region.As an important strategic city in the Yangtze River Delta,the air quality in Nanjing has drawn much concern from the whole society.In this paper,we used abundant observational data to study the spatial-temporal variation of air pollutants from 2013 to 2015 in Nanjing.Based on HYSPLIT and CWT models,we studied a heavy haze episode from November 28 to December 10,2013.We then applied the WRF-CMAQ model to simulate the haze pollution and investigate characteristics and origins of haze pollution in Nanjing city.The results in this paper showed that:?1?The annual average concentrations of ozone?O₃?,sulfur dioxide?SO₂?,carbon monoxide?CO?did not exceed their corresponding China National Air Quality Secondary Standard?CNAQSS?.The average annual concentrations of nitrogen dioxide?NO₂?,particulate matter(PM₁₀),and fine particulate matter(PM_2.5)were 53.2?g/m³,118.7?g/m³,and 69.3?g/m³ respectively,and exceeded their corresponding CNAQSS by 33%,69.6%,and 98%,respectively.PM_2.5 is the primary pollutant of ambient air quality in Nanjing.?2?The seasonal distributions of PM_2.5,PM₁₀,SO₂,NO₂ and CO mean concentrations were winter>autumn>spring>summer,while the variations of O₃ concentration were higher in spring and summer,but lower in autumn and winter.The diurnal variations of PM_2.5,PM₁₀,NO₂,and CO were similar with two peaks in a day which were consistent with the traffic flow.The O₃ diurnal variations showed a single peak variation with a peak value around 15:00.?3?The concentrations of PM_2.5 were affected by many factors,such as local primary emissions,secondary fine particulate production,regional transport and meteorological conditions.?4?The WRF-CMAQ model simulated PM_2.5 concentrations reasonable well with the Correlation Coefficient of 0.75.The model also captured the observed temperature,humidity and wind speed well.?5?The results of hybrid receptor model analysis showed that regional transport has an important effect on the PM_2.5 pollution in Nanjing,and the neighboring city of Nanjing,such as Suqian,Huaian,Hefei,and Hangzhou were the important potential source regions which were responsible for the heavy haze pollution in Nanjing.?6?The WRF-CMAQ model sensitivity tests indicated that the PM_2.5 concentrations can decrease by 40.8%in Nanjing city when the emissions were controled in the targeted areas identified by the CWT values.This showed that the CWT values can pinpoint the origins of heavy haze correctly although the further work is needed in the future.