Correction to "N-Nitrosodimethylamine Formation in Metformin Drug Products by the Reaction of Dimethylamine and Atmospheric NO2".

[This corrects the article DOI: 10.1021/acs.oprd.3c00274.].

Bio-diesel Fuel Material Supply in Vietnam and Its Current and Future Potentiality with a Focus on Rubber Seed Oil.

Diesel fuel usage in Vietnam is increasing rapidly, but most of it is imported from overseas. In this study, we investigated the possibility of popularizing bio-diesel fuel (BDF) made from Vietnamese origin resources as a sustainable energy solution. The world's energy cost fluctuates significantly depending on economic or political movements, especially after the Russian invasion of Ukraine began in 2022. This caused energy prices soar, attacking the global economy in a short period and requiring a wide range of energy supply sources. We aim to promote commercial BDF production in Vietnam for future energy security and contribution to the Vietnamese economy. Eight necessary factors were investigated to choose suitable material for BDF production. The factors are as follows: 1) material with Vietnamese origin, 2) sufficient and continuous supply volume, 3) sufficient quality to run diesel engines, including common-rail diesel engines, 4) inedibility, 5) low enough freezing point, 6) ease of collection, 7) affordability, and 8) availability of valuable elements in the material. If a suitable material candidate is not stable, it may be changed over time. In this study, the focus material was rubber seed oil. Because rubber production in Vietnam is quite stable with over 900,000 ha plantation area, and there is a potentiality to collect seeds and produce about 50,000 tons of BDF annually. In addition, the quality of rubber seeds based BDF is very high, such as low enough freezing point, etc. However, most of those rubber seeds are currently not collected and used.

Optimization of Procedure for Determining Dissolved Oxygen in Surface Water and Seawater Exploiting the UV-vis Absorption of Mn(III) Species.

We present an analytical method for dissolved oxygen based on the quantification of Mn(III) absorbance in a water sample. After Mn(II) reacts with the oxygen molecules in water, Mn(III) is formed and stabilized by hexa-metaphosphate under acidic conditions. The UV visible absorbance of Mn(III) is proportional to the oxygen concentration in the water sample. Compared to the Winkler method, the proposed method has the same accuracy (R = 0.9992 at 0 - 52 mg dm-3) but requires fewer reagents; furthermore, it does not involve titration. Interferences from nitrite and iodate were not observed. This procedure can be used to accurately and quickly determine the oxygen concentrations in different natural water sources, including seawater.

Development of a Photometric Method to Measure Molecular Oxygen in Water.

A photometric method to determine molecular oxygen in water was developed. When manganese(II) is oxidized by oxygen under alkaline conditions, the presence of polyphosphate can prevent precipitation due to a coacervate reaction. The oxidized manganese later dissolves in acid to form a pink Mn(III) species, which has a stable UV/vis spectrum. Monitoring of the oxygen concentration based on the absorbance of the pink Mn(III) species at 517 nm showed a strong correlation with both the Winkler method and an optical sensor. As a result, the present method can measure not only dissolved oxygen, but also fine bubbles oxygen in in the water sample with high reliability (0 - 26 mg dm-3, r2 = 0.9995). During this process, no significant interference from nitrite or metal ions was observed. The accuracy of the measurement was steady at high temperatures of the water samples (≤ 363 K).

A preliminary study on humic-like substances in particulate matter in Malaysia influenced by Indonesian peatland fires.

In this paper, ambient total suspended particulates (TSP) with a focus on humic-like substances (HULIS) are characterized based on intensive ground-based field samplings collected in Malaysia during non-haze and haze periods caused by peatland fires on the Indonesian island of Sumatra. Furthermore, concentrations of water-soluble organic carbon (WSOC) and carbon content of HULIS (HULIS-C) were determined, and fluorescence spectra of the HULIS samples were recorded by excitation emission matrix (EEM) fluorescence spectroscopy. The concentrations of WSOC and HULIS-C over the entire period ranged from 4.1 to 24 and 1.3 to 18 µgC m-3, respectively. The concentrations of WSOC and HULIS-C during the peatland fire-induced strong haze periods were over 4.3 and 6.1 times higher, respectively, than the average values recorded during the non-haze periods. Even during the light haze periods, the concentrations of WSOC and HULIS-C were significantly higher than their averages during the non-haze periods. These results indicate that peatland fires induce high concentrations of WSOC, particularly HULIS-C, in ambient TSP at receptor sites. EEM fluorescence spectra identified fulvic-like fluorophores at the highest intensity level in the EEM fluorescence spectra of the haze samples. A peak at excitation/emission (Ex/Em) ≈ (290-330)/(375-425) nm is also observed at high intensity, though this peak is normally associated with marine humic-like fluorophores. It is shown that a peak at Ex/Em ≈ (290-330)/(375-425) nm is not derived from marine sources only; furthermore, peatland fires are shown to be important contributors to HULIS around this peak.

Time Series Analysis of Climate and Air Pollution Factors Associated with Atmospheric Nitrogen Dioxide Concentration in Japan.

Nitrogen dioxide (NO2) is an air pollutant discharged from combustion of human activities. Nitrous acid (HONO), measured as NO2, is thought to impact respiratory function more than NO2. HONO and NO2 have an equilibrium relationship, and their reaction is affected by climate conditions. This study was conducted to discuss the extent of HONO contained in NO2, depending on the level of urbanization. Whether climate conditions that promote HONO production enhanced the level of NO2 measured was investigated using time series analysis. Climate and outdoor air pollution data measured in April 2009-March 2017 in urban (Tokyo, Osaka, and Aichi) and rural (Yamanashi) areas in Japan were used for the analysis. Air temperature had a trend of negative associations with NO2, which might indicate the decomposition of HONO in the equilibrium between HONO and NO2. The associations of relative humidity with NO2 did not have consistent trends by prefecture: humidity only in Yamanashi was positively associated with NO2. In high relative humidity conditions, the equilibrium goes towards HONO production, which was observed in Yamanashi, suggesting the proportion of HONO in NO2 might be low/high in urban/rural areas.

Lowest observed adverse effect level of pulmonary pathological alterations due to nitrous acid exposure in guinea pigs.

BACKGROUND: We previously demonstrated that continuous exposure to nitrous acid gas (HONO) for 4 weeks, at a concentration of 3.6 parts per million (ppm), induced pulmonary emphysema-like alterations in guinea pigs. In addition, we found that HONO affected asthma symptoms, based on the measurement of respiratory function in rats exposed to 5.8 ppm HONO. This study aimed to investigate the dose-response effects of HONO exposure on the histopathological alterations in the respiratory tract of guinea pigs to determine the lowest observed adverse effect level (LOAEL) of HONO. METHODS: We continuously exposed male Hartley guinea pigs (n = 5) to four different concentrations of HONO (0.0, 0.1, 0.4, and 1.7 ppm) for 4 weeks (24 h/day). We performed histopathological analysis by observing lung tissue samples. We examined samples from three guinea pigs in each group under a light microscope and measured the alveolar mean linear intercept (Lm) and the thickness of the bronchial smooth muscle layer. We further examined samples from two guinea pigs in each group under a scanning electron microscope (SEM) and a transmission electron microscope (TEM). RESULTS: We observed the following dose-dependent changes: pulmonary emphysema-like alterations in the centriacinar regions of alveolar ducts, significant increase in Lm in the 1.7 ppm HONO-exposure group, tendency for hyperplasia and pseudostratification of bronchial epithelial cells, and extension of the bronchial epithelial cells and smooth muscle cells in the alveolar duct regions. CONCLUSIONS: These histopathological findings suggest that the LOAEL of HONO is < 0.1 ppm.

Mechanism for sonochemical reduction of Au(III) in aqueous butanol solution under Ar based on the analysis of gaseous and water-soluble products.

When an aqueous Au(III) solution containing 1-butanol was sonicated under Ar, Au(III) was reduced to Au(0) to form Au particles. This is because various reducing species are formed during sonication, but the reactivity of these species has not yet been evaluated in detail. Therefore, in this study, we analyzed the effects of Au(III) on the rates of the formation of gaseous and water-soluble compounds (CH4, C2H6, C2H4, C2H2, CO, CO2, H2, H2O2, and aldehydes), and the rate of Au(III) reduction as a function of 1-butanol concentration. The following facts were recognized: 1) for Au(III) reduction, the contribution of the radicals formed by the pyrolysis of 1-butanol was higher than that of the secondary radicals formed by the abstraction reactions of 1-butanol with ·OH, 2) ·CH3 and CO acted as reductants, 3) the contribution of ·H to Au(III) reduction was small in the presence of 1-butanol, 4) aldehydes and H2 did not act as reductants, and 5) the types of species that reduced Au(III) changed with 1-butanol concentration.

Cyanide Formation in Freezer Stored Foods: Freezing of a Glycine and Nitrite Mixture.

Freezing is not always the best way to keep foods safely. Some reactions are known to be accelerated in ice. Furthermore, some other reactions that are not observed in solution are also promoted in ice. We found that the formation of nitrosamines through the reaction of an amine with a nitrite is accelerated in ice. Surprisingly, cyanide is formed through the reaction of glycine with nitrite in ice but not in solution. Amines are present in many kinds of foods. Nitrite is present in vegetables and is used as a food coloring agent and to inhibit the reproduction of Clostridium botulinum. The maximum amount of cyanide formed reaches a dangerous level, and the intake of this formed cyanide in a few tens of cubic centimeters causes some people to get headaches. These facts suggest that hazardous compounds could be generated in frozen processed foods. We report here the formation of cyanide and its possible formation pathway in ice. Finally, we propose a way to prevent cyanide formation in food under frozen conditions.

Ultrasound Assisted Cascade Extraction of Oil, Vitamin E, and Saccharides from Roselle (Hibiscus Sabdariffa L.) Seeds.

Roselle seeds, a waste biomass of the roselle calyx processing industry, were utilized to recover valuable compounds of oil, vitamin E, and water-soluble saccharides. Firstly, ultrasound-assisted extraction (UAE) and conventional stirring extraction were conducted for saccharide extraction, and the advantage of UAE was confirmed. Secondly, oil, vitamin E, and saccharides extracted from Vietnamese roselle seeds by UAE were analyzed for the first time. Oil of tri-, di-, and mono-glycerides, fatty acids of linoleic-, oleic-, palmitic-, and stearic-acids, vitamin E of γ- and α-tocopherol, and saccharides of sucrose, raffinose, stachyose, etc. were identified, and the amounts of these components were compared with those in other country's roselle seeds. Thirdly, cascade extraction of oil, vitamin E, and saccharides by UAE was investigated with solvents of hexane, hexane:ethyl acetate binary solvent, and water. The results indicated that the order of using solvents was very important for high and selective extraction: the best order to recover oil (almost 100%), vitamin E (95.7%), and saccharides (86.2%) was hexane, and then water.

Comparative study on water-soluble inorganic ions in PM2.5 from two distinct climate regions and air quality.

Recently, air quality has significantly improved in developed country, but that issue is of concern in emerging megacity in developing country. In this study, aerosols and their precursor gas were collected by NILU filter pack at two distinct urban sites during the winter and summer in Osaka, Japan and dry and rainy seasons in Ho Chi Minh City (HCMC), Vietnam. The aims are to investigate the contribution of water-soluble inorganic ions (WSIIs) to PM2.5, thermodynamic characterization and possible formation pathway of secondary inorganic aerosol (SIA). The PM2.5 concentration in Osaka (15.8 µg/m3) is lower than that in HCMC (23.0 µg/m3), but the concentration of WSIIs in Osaka (9.0 µg/m3) is two times higher than that in HCMC (4.1 µg/m3). Moreover, SIA including NH4+, NO3- and SO42- are major components in WSIIs accounting for 90% and 76% (in molar) in Osaka and HCMC, respectively. Thermodynamic models were used to understand the thermodynamic characterization of urban aerosols. Overall, statistical analysis results indicate that very good agreement (R2 > 0.8) was found for all species, except for nitrate aerosol in HCMC. We found that when the crustal species present at high amount, those compositions should be included in model calculation (i.e. in the HCMC situation). Finally, we analyzed the characteristics of NH4+- NO3-- SO42- system. A possible pathway to produce fine nitrate aerosol in Osaka is via the homogeneous reaction between NH3 and HNO3, while non-volatile nitrate aerosols can be formed by the heterogeneous reactions in HCMC.

Association between indoor nitrous acid, outdoor nitrogen dioxide, and asthma attacks: results of a pilot study.

The association between nitrogen dioxide (NO2) and asthma has been investigated. However, conventional NO2 assays measure nitrous acid (HONO) as NO2. In this pilot epidemiological observational study, we assessed exposure to indoor HONO and some air pollutants in pediatric asthma patients and examined possible association between exposure and asthma symptoms. Indoor HONO and nitric oxide (NO), which are primarily generated by the combustion of certain substances, were significantly associated with asthma attacks in 2010. In 2010, indoor HONO was closely correlated with indoor NO than with outdoor NO2. Conversely, in 2012, indoor HONO was closely correlated with outdoor NO2 and NO than with indoor NO2 and NO. Outdoor NO2 was significantly associated with asthma attacks in 2012. Our results highlight the need for further epidemiological studies of the association between indoor HONO and asthma symptoms using multivariate analyses to examine the role of NO2 in asthma symptoms. Abbreviations: CXCL1: the chemokine (C-X-C motif) ligand 1; EP: the entire study period; FP: the first half of study period; HONO: nitrous acid; NO: nitric oxide; NO2: nitrogen dioxide; OH radical: hydroxyl radical; SP: the second half of study period; TNF-α: tumor necrosis factor-α; US EPA: United States Environmental Protection Agency; WHO: World Health Organization.

Screening of fatty acids, saccharides, and phytochemicals in Jatropha curcas seed kernel as their trimethylsilyl derivatives using gas chromatography/mass spectrometry.

Jatropha curcas is a multipurpose plant, of which the seed kernel oil (up to 60% content) has been exploited for BDF production. In this report, we explored the various kinds of minor compounds of saccharides, phytochemicals, fatty acids (FAs), and amino acids in the seed kernel using gas chromatography/mass spectrometry (GC/MS) as their trimethylsilyl (TMS) derivatives. The homogenized seed kernels were extracted with methanol, and the extract was distributed into ethyl acetate/water phase. The components of each layer were derivatized with N, O-bis (trimethylsilyl) trifluoroacetamide (BSTFA) and their TMS derivatives were screened by GC/MS analysis. In ethyl acetate layer, the four FAs of palmitic acid, oleic acid, linoleic acid, and stearic acid were identified with total content of 12 wt% in kernel. In addition, the two tocochromanols of γ-tocopherol and γ-tocotrienol, and three phytosterols of campesterol, stigmasterol, and ß-sitosterol were also identified. Meanwhile, as the main saccharide components, di-saccharide of sucrose with content of 3 wt% in kernel, tri-saccharide of raffinose, and sugar alcohol of sorbitol and myo-inositol, were identified in aqueous layer. Furthermore, metabolites of amino acid, and a series of metabolite were also identified. These results suggested that the Jatropha curcas seed kernel can be applied to cascade use for metallic soap, liquid fuel, food and medical supplement, and cosmetics in addition to biodiesel production.

Effects of nitrous acid exposure on baseline pulmonary resistance and Muc5ac in rats.

We examined the baseline pulmonary resistance (RLung), baseline dynamic lung compliance (Cdyn), cytokine inductions, and histological alterations in rats exposed to nitrous acid (HONO) with secondary products of nitrogen dioxide (NO2) and nitric oxide (NO) to assess its biological effects. We exposed three groups of nine male F344 rats to different doses of HONO for six weeks (24 h/day). The cumulative values of HONO concentration were measured twice. The average concentrations of nitrogen oxide for each group were 5.8 parts per million (ppm) HONO with secondary products of 0.7 ppm NO2 and 2.3 ppm NO, 4.1 ppm HONO with 0.1 ppm NO2 and 0.6 ppm NO, and a clean air control. We measured baseline RLung and baseline Cdyn using tracheal cannulation. A tracheal tube was inserted into the trachea by tracheostomy, and lung function measurements (baseline RLung and baseline Cdyn) were conducted in mechanically ventilated rats. We measured mRNA levels of Cxcl-1, TNF-α, and Muc5ac in the right lung using quantitative RT-PCR, and observed histological alterations and the alveolar mean linear intercept (Lm) on the left lung. Our results demonstrated that HONO exposure significantly increased baseline RLung, Lm and Muc5ac expression, but did not affect baseline Cdyn or expression of Cxcl-1 and TNF-α. Further, we identified bronchial smooth muscle hypertrophy, pulmonary emphysema-like alterations in the alveolar duct centriacinar regions, and increased goblet cells in HONO-exposed rats. The present results suggest that HONO (with secondary products) adversely affects respiratory function, but that these pathologies may be unrelated to inflammation.

Sonochemistry of aqueous NaAuCl4 solutions with C3-C6 alcohols under a noble gas atmosphere.

The effect of the type of C3-C6 alcohol, solution temperature, and dissolved gas on the rate of Au(III) reduction was investigated in NaAuCl4 aqueous alcohol solution with a 200-kHz ultrasound irradiation system. It was confirmed in the presence of C3-C6 alcohol that more highly hydrophobic alcohols more effectively accumulated at the argon bubble interface region, and the reducing radicals formed here. To avoid changes in the bubble temperature during collapsing bubble, the effects of the solution temperature on the rate of Au(III) reduction and on the rate of formation of the gaseous compounds (CO, CO2, CH4, C2H2, C2H4, C2H6) were investigated in the presence of low concentration (1.0-mM) of 1-hexanol. Both of the rates showed a good relationship with the gas solubility: the amount of dissolved gas at different solution temperatures affected the number of high-temperature bubbles formed. The changes in the concentrations of the gaseous compounds formed from 1-hexanol degradation suggested that CO and the pyrolysis radicals acted as reductants. Finally, the effect of the type of dissolved gas was investigated in the presence of 1.0-mM Au(III) and 1.0-mM 1-hexanol. The rates of 1-hexanol degradation, Au(III) reduction, and gaseous compound formation increased in the order He

A 3-Step Chemiluminescence Method for Chemical Oxygen Demand Measurement.

Direct chemiluminescence emission from the reaction of acidic permanganate and organic compounds was employed for determining the chemical oxygen demand (COD) in water (1-step CL COD). Due to the diversity of organic pollutants in water, there are no standards for COD measurements, and many compounds do not show any chemiluminescence signal in the 1-step CL COD method. As a result, this method shows a low correlation with the conventional CODMn method. In this study, a new 3-step CL COD method was developed to overcome these drawbacks. The basic principle of the 3-step CL COD method is based on the principle of "back titration" in the CODMn method: (i) the sample is treated with permanganate under heating, (ii) the excess permanganate is treated with pyrogallol, and (iii) the excess pyrogallol is measured by the chemiluminescence reaction with permanganate. The reagent concentration, sample volume, and heating temperature were optimized, and the 3-step CL COD method successfully obtained the signal from some samples that cannot be detected by 1-step CL COD method. The calibration graph is linear in the range of 0 - 12.86 mg/L with a detection limit of 0.082 mg/L. This method is continuous, sensitive and low cost compared with the conventional method, and is applicable for on-site monitoring. The effect of the chloride ion was investigated, and showed an insignificant effect after two-times dilution of high-salinity samples. The correlation with the CODMn method for various organic compounds showed a good coefficient of determination, R2 = 0.9773 (n = 16).

Acceleration and Reaction Mechanism of the N-Nitrosation Reaction of Dimethylamine with Nitrite in Ice.

Some reactions (e.g., oxidation of nitrite, denitrification of ammonium) are accelerated in freeze-concentrated solution (FCS) compared to those in aqueous solution. Ice is highly intolerant to impurities, and the ice excludes those that would accelerate reactions. Here we show the acceleration of the N-nitrosation reaction of dimethylamine (DMA) with nitrite to produce N-nitrosodimethylamine (NDMA) in FCS. NDMA is a carcinogenic compound, and this reaction is potentially accelerated in frozen fish/meat. The eaction rate of the N-nitrosation reaction becomes fastest at specific pH. This means that it is a third-order reaction. Theoretical pH values of the peak in the third-order reaction are higher than the experimental one. Freeze-concentration of acidic solution causes pH decrement; however, the freeze-concentration alone could not explain the difference of pH values. The theoretical value was obtained under the assumption that no solute took part in ice. However, solutes are incorporated in ice with a small distribution coefficient of solutes into ice. This small incorporation enhanced the decrement of pH values. Using the distribution coefficient of chloride and sodium ion and assuming those of nitrite and DMA to explain the enhancement, we succeeded in estimating the distribution coefficients of nitrite: 2 × 10-3 and DMA: 3 × 10-2.

Binary Solvent Extraction of Tocols, γ-Oryzanol, and Ferulic Acid from Rice Bran Using Alkaline Treatment Combined with Ultrasonication.

Alkaline treatment (Alk) combined with ultrasound-assisted extraction (UAE) (Alk+UAE) was examined as a means of extracting tocols and γ-oryzanol from rice bran into an organic phase while simultaneously recovering ferulic acid into an aqueous phase. The tocols and γ-oryzanol/ferulic acid yields were determined using high-performance liquid chromatography with fluorescence and UV detection. The effects of extraction conditions were evaluated by varying the Alk treatment temperature and extraction duration. The maximum yields of tocols and γ-oryzanol were obtained at 25 °C over a time span of 30 min. When the temperature was increased to 80 °C, the yield of ferulic acid increased dramatically, whereas the recovery of γ-oryzanol slightly decreased. Employing the Alk+UAE procedure, the recovered concentrations of tocols, γ-oryzanol, and ferulic acid were in the ranges of 146-518, 1591-3629, and 352-970 µg/g, respectively. These results are in good agreement with those reported for rice bran samples from Thailand.

Characteristics of ammonia gas and fine particulate ammonium from two distinct urban areas: Osaka, Japan, and Ho Chi Minh City, Vietnam.

Continuous and simultaneous measurements of ammonia gas (NH3) and fine particulate ammonium (PM2.5NH4+) were performed in two distinct urban areas: Osaka, Japan, and Ho Chi Minh City (HCMC), Vietnam. Measurements were performed using a new online instrument. Two measurement periods were conducted during February 11-March 12, 2015 (cold period), and July 1-September 14, 2015 (warm period), at the urban site in Osaka, while 17 days of measurements, from May 21 to June 8, 2015, were conducted at the urban site in HCMC. The average NH3 concentration at the HCMC site was much higher than that at the Osaka site. The differences in the NH3 levels between the two cities are a result of their different emission sources. Traffic emission is a significant contributor to the NH3 levels within the urban area in Osaka. Conversely, the contribution of traffic emission to the NH3 levels in the HCMC urban area is negligible. With a population of around 8.5 million people living in the urban area of HCMC, the high NH3 level is due to human sources and poor waste management systems, especially because of the high temperature (30 °C) and dense population of the city (density up to 42,000 inhabitants per km2). In contrast to the NH3 levels, the highest PM2.5NH4+ level occurred during the cold period at the Osaka site, and the average level at this site was higher than that at the HCMC site. The availability of atmospheric acids, low temperature, and high humidity facilitates the formation of ammonium. Our results indicate that NH3 plays a key role in secondary inorganic aerosol formation; therefore, it contributes to a significant amount of PM2.5 at the Osaka site. In contrast, the high levels of PM2.5 observed at the HCMC site are likely from road traffic emission, mainly motorcycles, rather than secondary inorganic aerosol formation.

Gaseous nitrous acid (HONO) and nitrogen oxides (NOx) emission from gasoline and diesel vehicles under real-world driving test cycles.

Reactive nitrogen species emission from the exhausts of gasoline and diesel vehicles, including nitrogen oxides (NOx) and nitrous acid (HONO), contributes as a significant source of photochemical oxidant precursors in the ambient air. Multiple laboratory and on-road exhaust measurements have been performed to estimate the NOx emission factors from various vehicles and their contribution to atmospheric pollution. Meanwhile, HONO emission from vehicle exhaust has been under-measured despite the fact that HONO can contribute up to 60% of the total hydroxyl budget during daytime and its formation pathway is not fully understood. A profound traffic-induced HONO to NOx ratio of 0.8%, established by Kurtenbach et al. since 2001, has been widely applied in various simulation studies and possibly linked to under-estimation of HONO mixing ratios and OH radical budget in the morning. The HONO/NOx ratios from direct traffic emission have become debatable when it lacks measurements for direct HONO emission from vehicles upon the fast-changing emission reduction technology. Several recent studies have reported updated values for this ratio. This study has reported the measurement of HONO and NOx emission as well as the estimation of exhaust-induced HONO/NOx ratios from gasoline and diesel vehicles using different chassis dynamometer tests under various real-world driving cycles. For the tested gasoline vehicle, which was equipped with three-way catalyst after-treatment device, HONO/NOx ratios ranged from 0 to 0.95 % with very low average HONO concentrations. For the tested diesel vehicle equipped with diesel particulate active reduction device, HONO/NOx ratios varied from 0.16 to 1.00 %. The HONO/NOx ratios in diesel exhaust were inversely proportional to the average speeds of the tested vehicles. IMPLICATIONS: Photolysis of HONO is a dominant source of morning OH radicals. Conventional traffic-induced HONO/NOx ratio of 0.8% has possibly linked to underestimation of the total HONO budget and consequently underestimation of OH radical budget. The recently reported HONO/NOx ratio of ~1.6% was used to stimulate HONO emission, which resulted in increased HONO concentrations during morning peak hours and its impact of 14% OH increment in the morning. However, the results were still lower than the measured concentrations. More studies should be conducted to establish an updated traffic-induced HONO/NOx ratio.