AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Chemical Composition, Sources and Processes of Urban Aerosols during Summertime in Northwest China: Insights from a High Resolution Time-of-Flight Aerosol Mass Spectrometer
JIANZHONG XU, Qi Zhang, Min Chen, Jiawen Ren, Dahe Qin, State Key Laboratory of Cryospheric Sciences, China
Abstract Number: 429 Working Group: Aerosol Chemistry
Abstract Air pollution has become a serious issue in cities of China due to quick urbanization and industrialization in recent years. Here we report results from a field study conducted in Lanzhou, the capital of Gansu province in northwest China, during July 12th – Aug 7th, 2012. Lanzhou has been regarded as one of the most polluted cities in China mainly due to its unique valley topography. An Aerodyne high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was deployed along with a Scanning Mobility Particle Sizer (SMPS) and an Aethalometer to monitor the chemical variation of sub-micrometer aerosol (PM1) in real time. The average PM1 mass concentration during this study was 15.5 (± 9.5) micro-gram m$^(-3), with mean composition consisting of organics (43%), BC (19%), sulfate (16%), nitrate (9%), ammonium (8%), and chloride (4%). Positive matrix factorization (PMF) was applied to analyzing the organic mass spectra and identified four organic aerosol (OA) factors, representing, respectively, two primary OA (POA) emission sources (traffic and food cooking) and two secondary oxygenated OA (OOA) types – a semi-volatile (SV-OOA) and a low-volatility (LV-OOA) OOA. Black carbon (BC) and HOA displayed distinct diurnal patterns with a morning (~ 6:00-11:00) (Beijing Time) and an evening peak (~ 20:00-23:00) corresponding to the rush hours, while cooking OA (COA) peaked during lunch and dinner periods. The diurnal profiles of sulfate and LV-OOA displayed a broadly peak between ~7:00-15:00, while those of nitrate, ammonium and SV-OOA showed a narrower peak at ~ 8:00-13:00. The later morning and early afternoon peak in secondary aerosol pollution was likely caused by mixing down of pollutants aloft, which were decoupled from the boundary layer during night time. The micropulze lidar data have been used to check the vertical distribution of pollution. In addition, the time variations and their correlations with meteorological parameters have also been evaluated.