Characteristics and degradation of organic aerosols from cooking 1 sources based on hourly observation of organic molecular markers in 2 urban environment 3

17 Molecular markers in organic aerosol (OA) provide specific source information of PM 2.5 , and the contribution of 18 cooking organic aerosols to OA is significant, especially in urban environments. However, the low time resolution of 19 offline measurements limits the effectiveness in interpreting the tracer data, the diurnal variation of cooking emission and 20 the oxidation process. In this study, we used on-line thermal desorption aerosol gas chromatography mass spectrometry 21 (TAG) to measure organic molecular markers in fine particulate matter (PM 2.5 ) at an urban site in Changzhou, China. The 22 concentrations of saturated fatty acids (SFA), unsaturated fatty acids (uFAs), and oxidative decomposition products of 23 unsaturated fatty acids (ODPs) were measured every two hours to investigate the temporal variations and the oxidative 24 decomposition characteristics of uFAs in urban environment. The average concentration of total fatty acids (TFAs, sum than the enhancement of PM 2.5 (2.2 times) and OC (2.0 times) concentrations comparing polluted period to clean period. 28 The mean concentration of cooking aerosol in the polluted period (3.63 μg/m 3 ) was about 3.9 times higher than that in 29 the clean period (0.90 μg/m 3 ), which was similar to the trend of fatty acid. During the rising period of PM 2.5 , TFAs 30 concentration tends to reach the peak earlier than PM 2.5 . Fatty acids showed a clear diurnal variation. Linoleic acid 31 /Palmitic acid and Oleic acid /Palmitic acid ratios were significantly higher at dinning time, and closer to the source 32 profile. By performing backward trajectory clustering analysis, under the influence of short-distance air masses from 33 surrounding areas, the concentrations of TFAs and PM 2.5 were relatively high; while under the influence of air masses 34 from easterly coastal areas, the oxidation degree of unsaturated fatty acids emitted from local culinary sources were 35 higher. The effective rate constants ( k O ) for the oxidative degradation of oleic acid were estimated to be 0.12-0.41 h -1 , 36 which were lower than k L (the estimated effective rate constants of linoleic acid, 0.25-0.50 h -1 ). Both k O and k L showed a 37 significant positive correlation with O 3 , indicating that O 3 was the main night-time oxidants for uFAs in the Changzhou 38 City. Using fatty acids as tracers, cooking was estimated to contribute an average of 4.8% to PM 2.5 concentrations, rising 39 to 6.1% at dinner time; while the contribution to total OC is more than double the contribution to PM 2.5 . This study 40 investigates the variation of the concentrations and oxidative degradation of fatty acids and corresponding oxidation 41 products in ambient air, which can be a guide for the refinement of aerosol source apportionment, and provide scientific 42 support for the development of cooking source control policies. oxidation products of oleic acid, while 75 unsaturated fatty acids such as oleic and linoleic acids also react with other atmospheric oxidants, such as OH (Nah et al., 76 2014; Wang et al., 2020). 77 In this study, TAG was employed at an urban site in Changzhou, China, to investigate the variation of atmospheric 78 cooking-related fatty acids (FAs) with hourly resolution data (Ren et al., 2019). The aim of this study is to identify the 79 contribution of culinary emissions to ambient PM 2.5 with hourly organic molecules data and to investigate the oxidative 80 decomposition reactions of cooking-related FAs in an urban area. Results of this study could provide valid basis and 81 insights for the refinement of PM 2.5 source apportionment as well as atmospheric modelling. 82