Observations of nitrous acid and its relative humidity dependence in Shanghai

Nitrous acid, HNO2, is an important precursor of OH radicals in the troposphere. Measurements of HNO2 and NO2, using differential optical absorption spectroscopy （DOAS）, were performed in Shanghai, China for a period from October 22, 2004 to January 4, 2005. The mean （and median） hourly concentrations of HNO2 and NO2 during this period were 1.1 （0.7） ppb and 24 （21.4） ppb respectively. A correlation between HNO2/NO2 and PM10 mass concentrations was obtained. This correlation suggests that significant heterogeneous chemical production of HNO2 may occur through NO2 reactions on aerosol surfaces. This hypothesis was further supported by detailed analysis of selected pollution episodes in this study. At the same time, the water dependence of HNO2 formation was studied by analysis of relative humidity （RH）. It showed that the maximum HNO2/NO2 ratio was increased along with RH below 70% and inhibited at RH〉70%.

Removal of pathogenic indicator microorganisms during partial nitrification:the role of free nitrous acid

Digested wastewater contains pathogenic microorganisms and high ammonia concentrations,which can pose a potential risk to public health.Effective removal of pathogens and nitrogen is crucial for the post-treatment of digested wastewater.Partial nitrification-anammox is an energy-saving nitrogen removal process.Free nitrous acid(FNA),an intermediate product of partial nitrification,has the potential to inactivate microorganisms.However,the efficiency and mechanisms of FNA-related inactivation in pathogens during partial nitrification remains unclear.In this study,Enterococcus and Escherichia coli(E.coli)were selected to investigate the efficiency and mechanisms of FNA-related inactivation in partial nitrification process.The results revealed that 83%±13%and 59%±27%of E.coli and Enterococcus were removed,respectively,in partial nitrification process at FNA concentrations of 0.023−0.028 mg/L.When the concentration of FNA increased from 0 to 0.5 mg/L,the inactivation efficiencies of E.coli and Enterococcus increased from 0 to 99.9%and 89.9%,respectively.Enterococcus exhibited a higher resistance to FNA attack compared to E.coli.3D-laser scanning microscopy(3D-LSM)and scanning electron microscopy(SEM)revealed that FNA exposure caused the surface collapse of E.coli and Enterococcus,as well as visible pore formation on the surface of E.coli cells.4',6-Diamidino-2-phenylindole dihydrochloride n-hydrate(DAPI)/propidium iodide(PI)and biomolecule leakage confirmed that inactivation of E.coli and Enterococcus occurred due to breakdown of cell walls and cell membranes.These findings indicate that partial nitrification process can be used for the removal of residual pathogenic microorganisms.

New perspectives in free nitrous acid (FNA) uses for sustainable wastewater management

The biocidal effects of free nitrous acid (FNA) have found applications in multiple units in an urban wastewater system, including sewer networks, wastewater treatment processes, and sludge treatment processes. However, these applications are associated with chemical costs as both nitrite and acid are needed to produce FNA at the required levels. The recent discovery of novel acid-tolerant ammonia oxidizers offers the possibility to produce FNA from domestic wastewater, enabling the development of next-generation FNA-based technologies capable of achieving self-sustaining FNA production. In this study, we focus on the concept of in situ FNA generation facilitated by acid-tolerant ammonia oxidizers and highlight the multiple benefits it creates, after a brief review of the historical development of FNA-based technologies. We will discuss how wastewater systems can be made more energy-efficient and sustainable by leveraging the potential of acid-tolerant ammonia oxidizers.

Comparisons of measured nitrous acid(HONO) concentrations in a pollution period at urban and suburban Beijing, in autumn of 2014

To study the HONO formation mechanisms during a pollution period, a continuous measurement was performed in both urban and suburban aeras of Beijing. During this period, the PM2.5 concentrations increased to 201 and 137 ?g/m3 in urban and suburban areas, respectively. The concentrations of HONO, CO, SO2, O3, NO, NO2, NOx were 1.45 ppbv, 0.61 ppmv, 8.7 ppbv, 4.3 ppbv, 44.4 ppbv, 37.4 ppbv, 79.4 ppbv and 0.72 ppbv, 1.00 ppmv, 1.2 ppbv, 7.9 ppbv, 3.7 ppbv, 8.2 ppbv, 11.9 ppbv, in urban and suburban areas, respectively. To compare possible pathways of HONO formation in both sites, the contributions of direct emissions, heterogeneous formations, and homogeneous productions were studied. HONO/NO2 ratios in the two sites indicated that heterogeneous reactions of NO2 were more efficient in suburban areas. And in both urban and suburban areas, the increase of PM2.5 concentrations and RH would promote the conversion efficiency in RH that ranged from 0% to 85%. However, when RH was above 85%, the HONO formation slowed down. Moreover, the study of direct emissions and homogeneous reactions showed that they contributed to a majority of HONO increase in urban areas than the 20% contributions in suburban areas. It implied that the high NOx concentrations and NO concentrations in urban areas or in pollution periods would make direct emissions and homogeneous reactions become dominant in HONO formations.

Formation mechanisms of nitrous acid(HONO) during the haze and non-haze periods in Beijing,China

As an important precursor of hydroxyl radical(OH),nitrous acid(HONO)plays a significant role in atmospheric chemistry.Here,an observation of HONO and relevant air pollutants in an urban site of Beijing from 14 to 28 April,2017 was performed.Two distinct peaks of HONO concentrations occurred during the observation.In contrast,the concentration of particulate matter in the first period(periodⅠ)was significantly higher than that in the second period(periodⅡ).Comparing to HONO sources in the two periods,we found that the direct vehicle emissionwas an essential source of the ambient HONO during both periods at night,especially in periodⅡ.The heterogeneous reaction of NO_(2)was the dominant source in periodⅠ,while the homogeneous reaction of NO with OH was more critical source at night in periodⅡ.In the daytime,the heterogeneous reaction of NO_(2)was a significant source andwas confirmed by the good correlation coefficients(R^(2))between the unknown sources(P_(unknown))with NO_(2),PM_(2.5),NO_(2)×PM_(2.5)in periodⅠ.Moreover,when solar radiation and OH radicals were considered to explore unknown sources in the daytime,the enhanced correlation of P_(unknown)with photolysis rate of NO_(2)and OH(J_(NO_(2))×OH)were 0.93 in periodⅠ,0.95 in periodⅡ.These excellent correlation coefficients suggested that the unknown sources released HONO highly related to the solar radiation and the variation of OH radicals.

Long-term winter observation of nitrous acid in the urban area of Beijing

The particulate matter(PM)pollution has been significantly improved by carrying out various valid emission control strategies since 2013 in China.Meanwhile the variation trend of nitrous acid(HONO)is worthy to investigate due to its vital role in the atmospheric oxidation process.In this study,field observation in the winter is conducted to investigate the concentration of HONO in an urban area of Beijing.In the winter of 2019,the mean HONO concentration is 1.38 ppbV during the whole winter.Photo-enhanced NO_(2)heterogeneous reactions on the ground and aerosol surfaces were found as the possible daytime sources of HONO.Compared to O_(3),photolysis of HONO dominates the primary OH sources during the winter time.To understand the HONO pollution patterns by years variation,multi-year data is summarized and finds that primary pollutants including CO and NO decreased,but secondary pollutants i.e.,HONO(mostly generated via secondary process)increased.Our study highlights the requirement to mitigate secondary pollution by control HONO concentration.

剩余污泥有机质资源回收利用原位驱动晚期垃圾渗滤液深度脱氮——一种具有显著能源优势的创新生物技术

The sustainable recovery and utilization of sludge bioenergy within a circular economy context has drawn increasing attention,but there is currently a shortage of reliable technology.This study presents an innovative biotechnology based on free nitrous acid(FNA)to realize sustainable organics recovery from waste activated sludge(WAS)in-situ,driving efficient nitrogen removal from ammonia rich mature landfill leachate by integrating partial nitrification,fermentation,and denitrification process(PN/DN-F/DN).First,ammonia((1708.5±142.9)mg·L^(-1))in mature landfill leachate is oxidized to nitrite in the aerobic stage of a partial nitrification coupling denitrification(PN/DN)sequencing batch reactor(SBR),with nitrite accumulation ratio of 95.4%±2.5%.Then,intermediate effluent(NO_(2)^(-)-N=(1196.9±184.2)mg·L^(-1))of the PN/DN-SBR,along with concentrated WAS(volatile solids(VSs)=(15119.8±2484.2)mg·L^(-1)),is fed into an anoxic reactor for fermentation coupling denitrification process(F/DN).FNA,the protonated form of nitrite,degrades organics in the WAS to the soluble fraction by the biocidal effect,and the released organics are utilized by denitrifiers to drive NOx-reduction.An ultra-fast sludge reduction rate of 4.89 kg·m^(-3)·d^(-1) and nitrogen removal rate of 0.46 kg·m^(-3)·d^(-1) were realized in the process.Finally,F/DN-SBR effluent containing organics is refluxed to PN/DN-SBR for secondary denitrification in the post anoxic stage.After 175 d operation,an average of 19350.6 mg chemical oxygen demand organics were recovered per operational cycle,with 95.2%nitrogen removal and 53.4%sludge reduction.PN/DN-F/DN is of great significance for promoting a paradigm transformation from energy consumption to energy neutral,specifically,the total benefit in equivalent terms of energy was 291.8 kW·h·t^(-1) total solid.

Effect of substrate concentration on stability of anammox biofilm reactors

Ammonium and nitrite are two substrates of anammox bacteria, but they are also inhibitors under high concentrations. The performance of two anaerobic ammonium-oxidizing (anammox) upflow biofilm (UBF) reactors was investigated. The results show that anammox UBFs become unstable under nitrogen loading rate (NLR) applied higher than 1.0 g/(L·d). The consumptions of acidity in the anammox reaction lead to the increase of pH, which is as high as 8.70-9.05. Free nitrous acid concentration is accompanied to be lower than the affinity constant of anammox bacteria, and then starvation effect appears. Moreover, free ammonia concentration increases to 57-178 mg/L, resulting in inhibitory effect on the anammox bacteria. Both negative effects contribute to the instability of the anammox bioreactors.

Study on Fluorescence Property of Sparfloxacin Derivatizing System and its Application

In acid medium, sparfloxacin is oxidized by nitrous acid, then reacts with hydrobromic acid to form a new fluorescence substance, which can emit the strong fluorescence. which is 151 fold more than that of sparfloxacin itself. By this, a new sensitive method for the determination of sparfloxacin in human urine by derivative-synchronous fluorescence is presented with good results.

Advanced nitrogen removal via nitrite from municipal landfill leachate using a two-stage UASB–A/O system

A system consisting of a two-stage up-flow anaerobic sludge blanket （UASB） reactor and an anoxic/aerobic （A/O） reactor was used to treat municipal landfill leachate. Denitrification took place in the first stage of the UASB reactor （UASB1）. The chemical oxygen demand of the UASB1 effluent was further decreased in the second stage （UASB2）. Nitrification was accomplished in the A/O reactor. When diluted with tap water at a ratio of 1：1, the ammonia nitrogen concentration of the influent leachate was approximately 1200 mg· L^-1, whereas that of the system effluent was approximately 8-11 mg· L^-1, and the corresponding removal efficiency is about 99.08%. Stable partial nitrification was achieved in the A/O reactor with 88.61%-91.58% of the nitrite accumulation ratio, even at comparatively low temperature （ 16℃）. The results demonstrate that free ammonia （FA） concentrations within a suitable range exhibit a positive effect on partial nitrification. In this experiment when FA was within the 1-30 mgmg· L^-1 range, partial nitrification could be achieved, whereas when FA exceeded 280 mgmg· L^-1, the nitrification process was entirely inhibited. Temperature was not the key factor leading to partial nitrification within the 16-29 ℃ range. The inhibitory influence of free nitrous acid （FNA） on nitrification was also minimal when pH was greater than 8.5. Thus, FA concentration was a major factor in achieving partial nitrification.

Scoping Antifungal Activities of Various Forms of Chitosan Oligomers and Their Potential Fixation in Wood

Chitosan oligomers （average Dp-4） are known for their antifungal activity and wood decay resistance. These oligomers are susceptible to moisture, and promote yeast growth upon air exposure after a sufficient length of time. Chitosan oligomers of three different states viz. completely dried, freshly prepared and highly viscous form, were prepared to compare their in-vitro antifungal activities against three brown-rot fungi, two sapstain and one mould fungus using agar nutrient medium. Additionally, a mixture of chitosan oligomers and boric acid was used for wood treatment. The nutrient medium bioassay results show that all states of chitosan oligomers inhibited the growth of tested basidiomycetes fungi, but not sapstain and mould fungi. Subsequently, wood decay results confirm antifungal activity of chitosan oligomers plus boron against basidiomycetes, but highlighted their leachability upon water exposure.

Atmospheric HONO formation during and after the Spring Festival holidays in a coastal city of China

Nitrous acid(HONO)is an important source of hydrogen oxides(HOx),which affects air quality,the atmospheric oxidation capacity,and human health.Here,we present ambient measurements of the HONO concentrations in Zhuhai,a coastal city in Southern China,from February 7 to March 15,2021.The campaign was classified into two periods during(P1)and after(P2)the Spring Festival holidays.The average HONO mixing ratio during P2(1.19±0.85 ppbv)was much higher than that during P1(0.24±0.18 ppbv),likely due to the contribution of homogeneous HONO formation.During nighttime,the heterogeneous conversion rate during P2(0.0089/hr)was considerably higher than that during P1(0.0057/hr),suggesting a higher heterogeneous NO_(2) conversion potential.However,the heterogeneous NO_(2) conversion was the dominant way during P1 with a high percentage of 88%,while comparable ratios of heterogeneous and homogeneous formation were found(54%vs.46%)during P2,indicating that the homogeneous formation was also important during P2.During daytime,homogeneous reaction was the major known pathway,with a contribution of 16%during P1 and 27%during P2,leaving large unknown HONO sources which reasonably correlated with the photo-enhanced NO_(2) conversion.Two case scenarios were additionally explored,showing that there might be a primary emission source during one scenario(February 17-18)and vehicle emissions might be the major unknown HONO source for another scenario(March 3–5).The results suggest that large unknown daytime sources still exist which need more future ambient and laboratory studies.

Daytime HONO formation in the suburban area of the megacity Beijing, China

Nitrous acid （HONO）, as a primary precursor of OH radicals, has been considered one of the most important nitrogencontaining 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, Pon（HONO）net, was on average （from 05：00 to 19：00） 7.1 × 10^6 molecule/（cm^3 s）, 2.7 times higher than from 03 photolysis. This production rate demonstrates the important role of HONO in the atmospheric chemistry of megacity Beijing. An unknown HONO source （Punknown） with an average of 7.3 × 10^6 molecule/（cm^3 s） was derived from the budget analysis during daytime. Punknown provided four times more HONO than the reaction of NO with OH did. The diurnal variation of Punknown showed an apparent photo-enhanced feature with a maximum around 12：00, 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 Puknown. In this study, these mechanisms were validated against the observation-constraint Punknown. The reaction of exited NO2 accounted for only 6% of Puknown, and Punk 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.

Nitrifiers activity and community characteristics under stress conditions in partial nitrification systems treating ammonium-rich wastewater

Long-term exposure of nitrifiers to high concentrations of free ammonia （FA） and free nitrous add （FNA） may affect nitrifiers activity and nitrous oxide （N2O） emission. Two sequencing batch reactors （SBRs） were operated at influent ammonium nitrogen （NH4-N） concentrations of 800 mg/L （SBRH） and 33S mg/L （SBRL）, respectively. The NH4-N removal rates in SBRH and SBRL were around 2.4 and 1.0 g/L/day with the nitritation efficiencies of 99.3% and 95.7%, respectively. In the simulated SBR cycle, the N20 emission factors were 1.61% in SBRH and 2.30% in SBRL. N2O emission was affected slightly by FA with the emission factor of 0.22%-0.65%, while N2O emission increased with increasing FNA concentrations with the emission factor of 0.22%～3.96%. The dominant ammonia oxidizing bacteria （AOB） were Nitrosomonas spp. in both reactors, and their relative proportions were 38.89% in SBRH and 13.36% in SBRL. Within the AOB genus, a species （i.e., operational taxonomic unit [OTU] 76） that was phylogenetically identical to Nitrosomonas europaea accounted for 99.07% and 82.04% in SBRH and SBRL, respectively. Additionally, OTU 215, which was related to Nitrosomonas stercoris, accounted for 16.77% of the AOB in SBRL.

Effect of potential HONO sources on peroxyacetyl nitrate(PAN)formation in eastern China in winter

As an important secondary photochemical pollutant,peroxyacetyl nitrate(PAN)has been studied over decades,yet its simulations usually underestimate the corresponding observations,especially in polluted areas.Recent observations in north China found unusually high concentrations of PAN during wintertime heavy haze events,but the current model still cannot reproduce the observations,and researchers speculated that nitrous acid(HONO)played a key role in PAN formation.For the first time we systematically assessed the impact of potential HONO sources on PAN formation mechanisms in eastern China using the Weather Research and Forecasting/Chemistry(WRF-Chem)model in February of 2017.The results showed that the potential HONO sources significantly improved the PAN simulations,remarkably accelerated the RO x(sum of hydroxyl,hydroperoxyl,and organic peroxy radicals)cycles,and resulted in 80%–150%enhancements of PAN near the ground in the coastal areas of eastern China and 10%–50%enhancements in the areas around 35–40°N within 3 km during a heavy haze period.The direct precursors of PAN were aldehyde and methylglyoxal,and the primary precursors of PAN were alkenes with C>3,xylenes,propene and toluene.The above results suggest that the potential HONO sources should be considered in regional and global chemical transport models when conducting PAN studies.

NitroMAC：An instrument for the measurement of HONO and intercomparison with a long-path absorption photometer

Nitro MAC（French acronym for continuous atmospheric measurements of nitrogenous compounds） is an instrument which has been developed for the semi-continuous measurement of atmospheric nitrous acid（HONO）. This instrument relies on wet chemical sampling and detection using high performance liquid chromatography（HPLC）-visible absorption at540 nm. Sampling proceeds by dissolution of gaseous HONO in a phosphate buffer solution followed by derivatization with sulfanilamide/N-（1-naphthyl）-ethylenediamine. The performance of this instrument was found to be as follows： a detection limit of around 3 ppt with measurement uncertainty of 10% over an analysis time of 10 min. Intercomparison was made between the instrument and a long-path absorption photometer（LOPAP） during two experiments in different environments. First, air was sampled in a smog chamber with concentrations up to 18 ppb of nitrous acid. Nitro MAC and LOPAP measurements showed very good agreement. Then, in a second experiment, ambient air with HONO concentrations below250 ppt was sampled. While Nitro MAC showed its capability of measuring HONO in moderate and highly polluted environments, the intercomparison results in ambient air highlighted that corrections must be made for minor interferences when low concentrations are measured.