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Aerosols have a significant impact on both direct and indirect radiative effects and are considered to be one of the largest contributors to the uncertainty in global climate change assessment. In this study, continuous one-year-round in-situ observations of aerosol optical properties were conducted in the southeastern coastal city of Xiamen, China, and the effects of chemical composition on aerosol optical properties were analyzed to assess the environmental and climate effects of aerosols. The scattering coefficient (σ sp), absorption coefficient (σ ap), single scattering albedo (SSA) showed significant seasonal variations. The σ sp and σ ap showed obvious bimodal diurnal patterns, with peaks occurring in the morning peak and evening, while the diurnal patterns of SSA were reversed. The results of the chemical component-based estimation reconstruction of σ sp illuminated that OM, NH 4 NO 3 , (NH 4) 2 SO 4 were the main contributors to the σ sp. The concentration weighted trajectory (CWT) method was used to characterize the contributing sources of each chemical component affecting σ sp. The main contributing source areas were elucidated and varied slightly with species and season. The wind dependence analysis reflected that σ ap was mainly influenced by local emissions, while σ sp was affected by both local emissions and regional transport. The contribution sources of σ sp and σ ap were investigated using potential source contribution function (PSCF) method. The contributing source of σ sp and σ ap in Xiamen were clarified, and varied slightly with seasonal differences. This study revealed the aerosol optical properties in the southeastern coastal urban areas of China and provided a scientific basis for the estimation of the factors affecting climate change. • This is the first report of one-year-round in-situ observation of the aerosol optical properties in Xiamen. • Apparent diurnal variations of the aerosol optical properties were identified. • Regional transport and local emissions were responsible for the σ sp and σ ap , respectively. • NH 4 NO 3 dominated the contribution to the σ sp in winter, while OM dominated in the other seasons. [ABSTRACT FROM AUTHOR]

During the 2017 Xiamen BRICS summit, the chemical compositions (organics, sulfate, nitrate, ammonium, and chloride) of non-refractory submicron aerosol (NR-PM1) were measured by an Aerodyne Aerosol Chemical Speciation Monitor (ACSM). The field observation was conducted from 10 August to 30 September 2017 at the typical costal city Xiamen. Mean concentration of NR-PM1 was 17.56 µg m-3 with a range of 1.88 - 63.12 µg m-3. Organics was the most abundant component with a proportion of 43.15%, following by sulfate (34.44%), ammonium (12.73%), nitrate (9.00%), and chloride (0.68%). The concentrations of the NR-PM1 and its major chemical compositions reduced with the increasing of the control intensity and increased after the BRICS summit, which indicated to the significant effect of the control measures. Mass concentration of sulfate exceeded organics during the BRICS summit, which was different from other periods. Positive matrix factorization (PFM) analysis of organics obtained four components for organics, including HOA, BBOA, COA, and OOA. OOA account for 39.98% of the organic aerosols followed by COA (26.52%), BBOA (18.75%), and HOA (14.75%). The proportion OOA took increased obviously during the BRICS summit indicating to secondary formation enhanced. The episode (episode 1) observed in the early control period was contributed by organics and sulfate, while the other episode (episode 2) happened was mainly associated with organics and nitrate. A typhoon happened in the early control period, the high relative humidity after the typhoon promoted the heterogeneous reaction of secondary aerosols, which contributed a lot to the increasing of PM1 even under the control measures. The existence of nitrate can promote the formation of sulfate in episode 2. Regional transport and the formation of the secondary aerosols were the major contributors to episode 2. The result in this study helped to understand the formation mechanism and sources of submicron aerosol under the intense control measures and the normal status. [ABSTRACT FROM AUTHOR]