Nitrous acid (HONO), as a primary precursor of OH radicals, has been considered one of the most important nitrogen-containing species in the atmosphere. Up to 30% of primary OH radical production is attributed to the photolysis of HONO. However, the major HONO formation mechanisms are still under discussion. During the Campaigns of Air Quality Research in Beijing and Surrounding Region (CAREBeijing2006) campaign, comprehensive measurements were carried out in the megacity Beijing, where the chemical budget of HONO was fully constrained. The average diurnal HONO concentration varied from 0.33 to 1.2 ppbv. The net OH production rate from HONO, P (OH)(HONO)(net), was on average (from 05:00 to 19:00 h) 7.1 x 10(6) molecule/(cm(3) s), 2.7 times higher than from O-3 photolysis. This production rate demonstrates the important role of HONO in the atmospheric chemistry of megacity Beijing. An unknown HONO source (P (unknown)) with an average of 7.3 x 10(6) molecule/(cm(3) s) was derived from the budget analysis during daytime. P (unknown) provided four times more HONO than the reaction of NO with OH did. The diurnal variation of P (unknown) showed an apparent photo-enhanced feature with a maximum around 12:00 h, which was consistent with previous studies at forest and rural sites. Laboratory studies proposed new mechanisms to recruit NO2 and J(NO2) in order to explain a photo-enhancement of of P (unknown). In this study, these mechanisms were validated against the observation-constraint P (unknown). The reaction of exited NO2 accounted for only 6% of P (unknown), and P (unknown) poorly correlated with [NO2] (R = 0.26) and J(NO2)[NO2] (R = 0.35). These results challenged the role of NO2 as a major precursor of the missing HONO source.
Nitrous acid (HONO), as a primary precursor of OH radicals, has been considered one of the most important nitrogen-containing species in the atmosphere. Up to 30% of primary OH radical production is attributed to the photolysis of HONO. However, the major HONO formation mechanisms are still under discussion. During the Campaigns of Air Quality Research in Beijing and Surrounding Region (CAREBeijing2006) campaign, comprehensive measurements were carried out in the megacity Beijing, where the chemical budget of HONO was fully constrained. The average diurnal HONO concentration varied from 0.33 to 1.2 ppbv. The net OH production rate from HONO, P (OH)(HONO)(net), was on average (from 05:00 to 19:00 h) 7.1 x 10(6) molecule/(cm(3) s), 2.7 times higher than from O-3 photolysis. This production rate demonstrates the important role of HONO in the atmospheric chemistry of megacity Beijing. An unknown HONO source (P (unknown)) with an average of 7.3 x 10(6) molecule/(cm(3) s) was derived from the budget analysis during daytime. P (unknown) provided four times more HONO than the reaction of NO with OH did. The diurnal variation of P (unknown) showed an apparent photo-enhanced feature with a maximum around 12:00 h, which was consistent with previous studies at forest and rural sites. Laboratory studies proposed new mechanisms to recruit NO2 and J(NO2) in order to explain a photo-enhancement of of P (unknown). In this study, these mechanisms were validated against the observation-constraint P (unknown). The reaction of exited NO2 accounted for only 6% of P (unknown), and P (unknown) poorly correlated with [NO2] (R = 0.26) and J(NO2)[NO2] (R = 0.35). These results challenged the role of NO2 as a major precursor of the missing HONO source.
Eighty-seven soil samples collected from North China were analyzed for Dechlorane Plus (DP). The concentrations of DP ranged from not detectable (ND) to 12.21 ng/g with a mean of 0.55 ng/g. The mean concentrations of total DP and syn-DP in four regions of North China were in the following order: Jingjin (Beijing and Tianjin) > Shandong > Shanxi > Hebei, while the mean concentrations of anti-DP in the four regions were in a different order: Shandong > Jingjin > Shanxi > Hebei. The mean f (syn) values for Jingjin (0.27), Hebei (0.24), and Shanxi (0.24) were close to 0.25, while the mean f (syn) value for Shandong (0.31) was closer to 0.35. In addition, the f (syn) value for Shandong was significantly higher (P < 0.01) than those of the other regions (Jingjin, Heibei, and Shanxi), indicating specific sources of DP. Syn-DP displayed a strong linear relationship with anti-DP (R (2) = 0.74), indicating that no obvious stereoselective process occurred in the soil of North China. Ordinary kriging was undertaken to map the spatial patterns of DP. High concentrations of DP in soils were present in south of Shanxi, central Hebei, south of Tianjin, and the south and northeast of Shandong, which were suggested to be connected with human activities such as e-waste dismantling.
alpha-Pinene/NOx and alpha-pinene/HONO photooxidation experiments at varying humidity were conducted in smog chambers in the presence or absence of FeSO4 seed particles. FeSO4 seed particles decrease SOA mass as long as water was present on the seed particle surface, but FeSO4 seed particles have no decreasing effect on SOA under dryer conditions at 12% relative humidity (RH). The decreasing effect of FeSO4 seed particles on the SOA mass is proposed to be related to oxidation processes in the surface layer of water on the seed particles. Free radicals, including OH, can be formed from catalytic cycling of Fe2+ and Fe3+ in the aqueous phase. These radicals can react further with the organic products of alpha-pinene oxidation on the seed particles. The oxidation may lead to formation of smaller molecules which have higher saturation vapor pressures and favor repartitioning to the gas phase, and therefore, reduces SOA mass. (C) 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).
Based on our proposed self-terminating gate recess etching technique, normally-off recess-gated AlGaN/GaN MOSFET has been demonstrated with a novel method using GaN cap layer (CL) as recess mask, which, as a result, simplifies the device fabrication process and lowers the fabrication cost. The GaN CL is capable of acting as an effective recess mask for the gate recess process, which includes a thermal oxidation for 45 min at 650 degrees C followed by 4-min etching in potassium hydroxide (KOH) at 70 degrees C. After gate recess process, no obvious change is observed in terms of the surface morphology of the GaN CL, the contact resistance of the Ohmic contact formed directly on the GaN CL as well as the sheet resistance of the two-dimensional electron gas (2-DEG) channel layer under the GaN CL. The fabricated device exhibits a threshold voltage (V-th) as high as 5 V, a maximum drain current (I-dmax) of similar to 200 mA/mm, a high ON/OFF current ratio of similar to 10(10) together with a low forward gate leakage current of similar to 10(-5) mA/mm. Meanwhile, the OFF-state breakdown voltage (V-br) of the device with gate-drain distance of 6 mu m is 450 V.
Both ammonia-oxidizing bacteria (AOB) and archaea (AOA) might be the key microorganisms in ammonia conversion in ecosystems. However, the depth-related change of AOA and AOB in sediment ecosystem is still not clear. The relative contribution of AOA and AOB to nitrification in wetland sediment remains also unclear. Moreover, information about ammonia-oxidizing microorganisms in high-altitude freshwater wetland is still lacking. The present study investigated the relative abundances and community structures of AOA and AOB in sediments of a high-altitude freshwater wetland in Yunnan Province (China). Variations of the relative abundances and community structures of AOA and AOB were found in the wetland sediments, dependent on both sampling site and sediment depth. The relative abundances of AOA and AOB (0.04-3.84 and 0.01-0.52 %) and the AOA/AOB ratio (0.12-4.65) showed different depth-related change patterns. AOB community size was usually larger than AOA community size. AOB diversity was usually higher than AOA diversity. AOA diversity decreased with the increase of sediment depth, while AOB diversity showed no obvious link with the sediment depth. Pearson's correlation analysis showed that AOA diversity had a positive significant correlation with available phosphorus. Nitrosospira-like sequences, with different compositions, predominated in the wetland sediment AOB communities. This work could provide some new insights toward nitrification in freshwater sediment ecosystems.
This paper proposes a novel implementation of a high frequency rectifier, which is realised using the simplified real frequency technique. The optimum impedances presented at the diode package plane are found from source-pull simulation over a broad frequency range. The implemented broadband rectifiers show good performance in terms of efficiency and bandwidth. Using a HSMS 2820 Schottky diode device, greater than 50 % efficiency has been measured from 1.25 GHz to 2.25 GHz. Furthermore, greater than 60 % efficiency with 14 dB (from 12 dBm to 26 dBm) input power dynamic range is achieved at 1.8 GHz. Peak efficiency of 77 % is obtained at the input power of 23 dBm. The high efficiency over such a large bandwidth is believed to be the best reported to data in open literature at these frequencies.
This paper proposes a novel configuration of the rectifier which is realised using a high impedance inductor. It removes the input matching network concerning the trade-off of the efficiency and bandwidth. The rectifier with better than 40 % efficiency is designed and measured across the frequency band from 40 MHz to 4740 MHz. The peak RF-DC conversion efficiency of 60.3 % is achieved at 1 GHz operating frequency with 23 dBm incident power. In addition, a minimum of 2 V output DC voltage and greater than 40 % efficiency with 5 dB input power dynamic range from 20 dBm to 25 dBm is obtained covering the entire band.
