Highlights Ultrasound improved the strength, textural properties and WHC of surimi gel. Ultrasound promoted the unfolding of α-helix structures of protein. Ultrasound facilitated the formation of more compact microstructures. Ultrasonic-assisted preheating treatment had the most remarkable improvement on the gel properties of surimi.

Highlights DAG pre-emulsion with good stability was obtained by ultrasound. DAG pre-emulsion increased whiteness of composite gels. DAG pre-emulsion improved the gel strength and WHC of composite gels. Composite gels containing DAG pre-emulsion formed a more compact 3D network structure.

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On a global scale, biomass burning has been recognized as the primary source of fine carbonaceous particles and the second-largest source for total trace gases (Akagi et al., 2011;Stockwell et al., 2015;Yokelson et al., 2013). Pollutants emitted during the burning process can contribute significantly to local and regional air pollution (Chen et al., 2017;Crilley et al., 2015;Languille et al., 2020). The reactive species emitted participate in the reactions in the atmosphere producing secondary pollutants, such as secondary organic aerosols and ozone (O 3 ), which can amplify the impact of primary pollutants (Alvarado et al., 2015;Gilman et al., 2015;Yokelson et al., 2013). Recognizing and quantifying the amount of biomass burning emissions can help to understand the local source attribution and greatly enhance the accuracy of air quality forecasting in the downwind areas (

The flow over a square cylinder controlled by a slot synthetic jet positioned at the front surface is investigated experimentally at different excitation frequencies. The Reynolds number based on the free-stream velocity and the side length of the square cylinder is 1000. The flow visualization was conducted using the laser-induced fluorescence technique. The velocity fields upstream and downstream of the square cylinder were measured synchronously with the two-dimensional time-resolved particle image velocimetry technique. Both the evolution of vortex structures and the characteristic frequencies of upstream and downstream flow fields are presented. The flow dynamics vary significantly with the excitation frequency at a fixed stroke length. During one excitation cycle, the synthetic jet vortex pair deflects to one side and later swings to the other side at a quite small excitation frequency of $f_{e}/f_{0}=0.6$, while it only deflects toward one side and does not turn to the other side at $f_{e}/f_{0}=1.0$. Compared with the natural case, the wake characteristics for the above two cases are not changed much by the synthetic jet adopted. At a moderate excitation frequency of $f_{e}/f_{0}=2.0$, the synthetic jet deflects upwards and downwards alternatively. The upstream flow field has a dominant frequency identical to half of the excitation frequency. Under the perturbations of the synthetic jet, two wake vortex pairs are formed per shedding cycle with a shedding frequency equal to that of the square cylinder without control. At a higher excitation frequency of $f_{e}/f_{0}=3.4$, the synthetic jet keeps deflecting to one side, and the upstream flow field is governed by the excitation frequency. The flow separation on the deflected side is suppressed effectively, and no periodic vortex shedding can be observed in the wake. Statistically, the velocity profiles also change with control. The recirculation bubble length in the wake is shortened, and the time-averaged velocity fluctuation is weakened remarkably. The control effects of the synthetic jet and the continuous jet are compared in this paper when placed at the front surface of a square cylinder.

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Abstract. Ambient nitrate has been of increasing concern in PM2.5, while there are still large uncertainties in quantifying the formation of nitrate aerosol. The formation pathways of nitrate aerosol at an urban site and a suburban site in the Pearl River Delta (PRD) are investigated using an observation-constrained box model. Throughout the campaigns, aerosol pollution episodes were constantly accompanied with the increase in nitrate concentrations and fractions at both urban and suburban sites. The simulations demonstrate that chemical reactions in the daytime and at night both contributed significantly to formation of nitrate in the boundary layer at the two sites. However, nighttime reactions predominantly occurred aloft in the residual layer at the urban site, and downward transport from the residual layer in the morning is an important source (53 %) for surface nitrate at the urban site, whereas similar amounts of nitrate were produced in the nocturnal boundary layer and residual layer at the suburban site, which results in little downward transport of nitrate from the residual layer to the ground at the suburban site. We show that nitrate formation was in the volatile-organic-compound-limited (VOC-limited) regime at the urban site, and in the transition regime at the suburban site, identical to the response of ozone at both sites. The reduction of VOC emissions can be an efficient approach to mitigate nitrate in both urban and suburban areas through influencing hydroxyl radical (OH) and N2O5 production, which will also be beneficial for the synergistic control of regional ozone pollution. The results highlight that the relative importance of nitrate formation pathways and ozone can be site-specific, and the quantitative understanding of various pathways of nitrate formation will provide insights for developing nitrate and ozone mitigation strategies.