High levels of HONO have frequently been observed in Chinese haze periods and underestimated by current models due to some unknown sources and formation mechanisms. Combining lab-chamber simulations and field measurements in Xi'an and Beijing, China, we found that NH 3 can significantly promote HONO formation via the reduction−oxidation of SO 2 with NO 2 in the aqueous phase of hygroscopic particles (e.g., NaCl). Concentrations of HONO formed in the aerosol phase showed an exponential increase (R 2 = 0.91) with NH 3 levels under the chamber conditions and a linear growth with NH 3 levels in the two Chinese cities. The uptake coefficient of NO 2 on NaCl particles ranged from 2.0 × 10 −5 to 1.7 × 10 −4 , 3−4 orders of magnitude larger than that on water droplets. Our results further showed that HONO formed from the aerosol phase accounted for 4−33% of the total in the chamber, indicating that aerosol-phase formation is an important source of HONO in China, especially in haze periods. Since NH 3 , SO 2 , and NO 2 abundantly coexist in China, the positive effect of NH 3 on HONO formation could enhance the atmospheric oxidizing capacity in the country, causing severe secondary aerosol pollution. Our work suggests that NH 3 emission control is imperative for mitigating air pollution in China.

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High-performance chlorine-resistant thin-film composite (TFC) membranes with zwitterions were fabricated by in situ surface modification of polyamide with 2,6-diaminopyridine and the subsequential quaternization with 3-bromopropionic. The successful modification of the TFC polyamide surface with zwitterions was confirmed by various characterizations including surface chemistry, surface hydrophilicity, and surface charge. The transport performance of the membrane was measured in both of the cross-flow reverse osmosis (RO) and forward osmosis processes, and the results showed that the modified TFC membrane improved both of its water permeability and perm-selectivity with the increased A and A/B ratios upon modification with zwitterions. The chlorination challenging experiments were performed to demonstrate that the modified membrane enhanced its chlorine resistance without affecting its salt rejection upon 16 000 ppm•h chlorination exposure. A chlorination mechanism study illustrated that the modified membrane with zwitterions could prevent the Orton rearrangement of the benzene ring of the polyamide layer. Importantly and excitingly, the optimal chlorinated TFC membrane with zwitterions achieved a very high water flux of 72.15 ± 2.55 LMH with 99.67 ± 0.09% of salt rejection in the cross-flow RO process under 15 bar.

Particle Swarm Optimization (PSO) is a popular metaheuristic for deterministic optimization. Originated in the interpretations of the movement of individuals in a bird flock or fish school, PSO introduces the concept of personal best and global best to simulate the pattern of searching for food by flocking and successfully translate the natural phenomena to the optimization of complex functions. Many real-life applications of PSO cope with stochastic problems. To solve a stochastic problem using PSO, a straightforward approach is to equally allocate computational effort among all particles and obtain the same number of samples of fitness values. This is not an efficient use of computational budget and leaves considerable room for improvement. This paper proposes a seamless integration of the concept of optimal computing budget allocation (OCBA) into PSO to improve the computational efficiency of PSO for stochastic optimization problems. We derive an asymptotically optimal allocation rule to intelligently determine the number of samples for all particles such that the PSO algorithm can efficiently select the personal best and global best when there is stochastic estimation noise in fitness values. We also propose an easy-to-implement sequential procedure. Numerical tests show that our new approach can obtain much better results using the same amount of computational effort.