Abstract: Background, aim, and scope Frequent occurrence of haze days has caused widespread concern in last decade. Atmospheric aerosol can absorb and scatter solar radiation, affect regional and global climate; reduce atmospheric visibility, causing inconvenience to daily travel, and deposit in the human respiratory tract and lungs, affecting human health. Therefore, to perform a series of research on the chemical composition, characteristics, evolution mechanism of atmospheric aerosol and the source apportionment of organic aerosol, which are closely related to the formation of haze, is essential. This study aims to carry out targeted research on spring aerosol after heating season. Hoping to get a comprehensive understand of the characteristics, sources and seasonal features of fine particulate matter (PM). Materials and methodsA 13-day online real-time measurement was conducted using a Quadrupole-Aerosol Chemical Speciation Monitor (Q-ACSM) equipped with gaseous analyzers and an Aethalometer. The ACSM dataset was analyzed by the standard ACSM data analysis software in Igor Pro (WaveMetrics, Inc., Lake Oswego, Oregon USA). The chemical composition, mass concentrations and daily variations of the submicron aerosol were obtained after that. What’s more, Positive Matrix Factorization was used to perform the source apportionment on the ACSM organic data as implemented by the Multiliner Engine (ME-2) via the interface SoFi (Source Finder) coded in Igor Wavematrics. Results The average mass concentration of PM1 during the whole observation period was 58.0 μg m-3. OA was the component with the largest contribution (41.4%), followed by nitrate 27.3%, ammonium 15.0%, sulfate 7.9%, black carbon 4.8% and chloride 3.6%. According to result of the source apportionment, organic aerosol consisted of four primary sources: HOA, COA, CCOA, BBOA and a secondary source OOA. The mass fractions were 10.3%, 9.3%, 18.0%, 8.0% and 54.4%, respectively. Discussion The concentration of PM1 during the whole observation period was significantly lower than that of the 2014 winter, which may be related to the end of heating season. OA was the most contributing component in PM1, followed by nitrate. The vigorous implementation of desulfurization technology in coal-fired power plants had greatly reduced the emission of SO2, so that the sulfate concentration was low throughout the whole period. Factors of organic aerosol were well correlated with external markers, and the mass spectra were consistent with previous studies. In addition, different pollution events occurred during the observation period, we found the accumulation process of pollutants was slow, but the removal process was faster. Through the comparison among different pollution events, effects of gases, meteorological factors and regional transmission on the formation of atmospheric pollution were discussed in depth. Finally, the relationship between air mass transmission and pollution formation was also analyzed by using the backward trajectory. Conclusions Even though some pollution prevention and control measures have begun to bear fruit, the situation of air pollution in China is still very serious. Among the components of PM1, organic aerosol and nitrate were the major components. OOA was the highest proportion factor of organic aerosol This study found that compared with clean stage, the pollution period was often accompanied by higher relative humidity, lower wind speed and higher gaseous precursor concentrations. And the mass fraction of secondary aerosol (sulfate, nitrate and OOA) will increase significantly from clean to pollution episode. Recommendations and perspectives These results show that it is of great significance to pay attention to the formation and oxidation mechanism of secondary aerosol (organic and inorganic) and to control emissions of precursors of secondary pollutants.
Keywords: PM1; source apportionment; secondary aerosol