Toward Building a Physical Proxy for Gas-Phase Sulfuric Acid Concentration Based on Its Budget Analysis in Polluted Yangtze River Delta, East China

Gaseous sulfuric acid (H2SO4) is a crucial precursor for secondary aerosol formation, particularly for new particle formation (NPF) that plays an essential role in the global number budget of aerosol particles and cloud condensation nuclei. Due to technology challenges, global-wide and long-term measurements of gaseous H2SO4 are currently very challenging. Empirical proxies for H2SO4 have been derived mainly based on short-term intensive campaigns. In this work, we performed comprehensive measurements of H2SO4 and related parameters in the polluted Yangtze River Delta in East China during four seasons and developed a physical proxy based on the budget analysis of gaseous H2SO4. Besides the photo-oxidation of SO2, we found that primary emissions can contribute considerably, particularly at night. Dry deposition has the potential to be a non-negligible sink, in addition to condensation onto particle surfaces. Compared with the empirical proxies, the newly developed physical proxy demonstrates extraordinary stability in all the seasons and has the potential to be widely used to improve the understanding of global NPF fundamentally.Peer reviewe

Fabrication Method for the High-Accuracy Optical Fiber Delay Line with Specified Length

We propose a novel scheme for fabricating high-accuracy optical fiber delay lines (OFDLs). The fabrication system integrates a self-designed optical fiber cutting device and a high-accuracy fiber length measurement module based on optical frequency domain reflectometry. The optical fiber cutting device can cleave optical fibers to a specific length with the help of the motorized stage. The accuracy of fiber-cutting was determined by the positional accuracy of the motorized stage, which can reach several microns or even lower. This integrated design significantly reduces the errors and uncertainties introduced by fiber-cutting. To test, a set of OFDLs of a certain length was fabricated by this system. The deviation from the desired fiber length was kept below 50 μm, thus proving high fabrication accuracy and repeatability

A Tunable Dual-Passband Microwave Photonic Filter Based on Optically Injected Distributed Feedback Semiconductor Lasers and Dual-Output Mach-Zehnder Modulator

In this paper, a novel approach to achieving a wideband tunable dual-passband microwave photonic filter (MPF) is proposed based on optical-injected distributed feedback (DFB) semiconductor lasers and a dual-output Mach–Zehnder modulator (DOMZM). The fundamental concepts for realizing the MPF are the wavelength-selective amplification effect and the period-one oscillation state under optically injected DFB lasers. These effects provide a widely tunable range of center frequency, along with high flexibility and low insertion loss. The proposed MPF is experimentally demonstrated, showing that the dual-passband center frequency in the MPF can be tuned independently from 19 to 37 GHz by adjusting the detuning frequency and injection ratio. Meanwhile, the insertion loss of the system is about 15 dB when there is no optical or electrical amplifier in the MPF link. The out-of-band suppression ratio of the MPF is more than 20 dB, which can be improved by adjusting the power of the two optical signals