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PM2.5 is inhalable particulate with a diameter less than 2.5 μM that easily enters the lungs and causes diseases and non-accidental death. The generation and dissipation of PM2.5 are strongly affected by a variety of environmental factors, thus the concentration of PM2.5 is presumably predictable with the observations of environmental conditions. This paper used multi-year meteorological and PM2.5 concentration data across multiple megacities in China (Beijing, Chengdu, and Shenyang) and sought for a universal predictive model. Our results showed that data-driven machine-learning model was able to not only capture PM2.5 dynamics at the city where the model was trained but also could be generalized to predict PM2.5 concentrations over other cities. Therefore, the modeling results indicated a universally existing predictive relationship between PM2.5 source-sink dynamics and the environmental drivers.

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High step-up voltage gain nonisolated DC-DC converter have attracted much attention in photovoltaic, fuel cells and other renewable energy system applications. In this paper, by combining input current ripple-free boost cell with coupled-inductor voltage-doubler cell, an input current ripple-free high voltage gain nonisolated converter is proposed. In addition, passive lossless clamp circuit is adopted to recycle the leakage inductor energy and to reduce the voltage spike across the power switch. By utilizing voltage-doubler cell consisting of diode and capacitor, the voltage stress of switch is further reduced and the resonance between the leakage inductor and the stray capacitor of the output diode is eliminated. A low switch-on-resistance low-voltage-rated MOSFET can therefore be employed to reduce the conduction loss and cost. The reverse recovery loss of output diode is reduced, and the efficiency of converter can be improved. Furthermore, the proposed converter can achieve nearly zero input current-ripple and make the design of electromagnetic interference (EMI) filter easy. Steady state analysis and operation mode of the converter is performed. Finally, experimental results are presented to verify the analysis results of the proposed converter.