Atmospheric nitrous acid (HONO) at a rural coastal site in North China: Seasonal variations and effects of biomass burning

Nitrous acid (HONO) plays a significant role in atmospheric chemistry due to its contribution to hydroxyl radical (OH). However, no scientific consensus has been achieved about the daytime HONO formation mechanisms. To identify the seasonal variations of HONO chemistry and the impacts of biomass burning (BB), we performed a two-phased field study in winter-spring and summer (covering a harvest season) in 2017 at a rural coastal site in North China. Though the mean HONO concentration in winter-spring (0.26 +/- 0.28 ppbv) was higher than in summer (0.17 + 0.19 ppbv), the maximum HONO concentrations were comparable (similar to 2 ppbv) in the two campaigns. Both the HONO/NOx ratio and nocturnal heterogeneous conversion efficiency of HONO (C-HONO) in summer were over twice of that in winter-spring. The daytime budget analysis also revealed that the strength of P(othe)r (i.e., the HONO sources apart from the reaction of OH + NO) in summer was double of that in winter-spring. BB affected the HONO concentration by enhancing the contribution of heterogeneous HONO production on the aerosol surface but weakening the role of photo-related HONO formation. HONO photolysis was a significant source of OH in both winter-spring and summer, and its contribution could be further enhanced during the BB episode in summer. Our study demonstrates the significant seasonal variations of HONO and the effects of BB, and suggests needs for more multi-season observations and considerations of BB, especially during the harvest time, in HONO research

Seasonal variation in oxygenated organic molecules in urban Beijing and their contribution to secondary organic aerosol

Oxygenated organic molecules (OOMs) are crucial for atmospheric new particle formation and secondary organic aerosol (SOA) growth. Therefore, understanding their chemical composition, temporal behavior, and sources is of great importance. Previous studies on OOMs mainly focus on environments where biogenic sources are predominant, yet studies on sites with dominant anthropogenic emissions, such as megacities, have been lacking. Here, we conducted long-term measurements of OOMs, covering four seasons of the year 2019, in urban Beijing. The OOM concentration was found to be the highest in summer (1.6 x 10(8) cm(-3)), followed by autumn (7.9 x 10(7) cm(-3)), spring (5.7 x 10(7) cm(-3)) and winter (2.3 x 10(7) cm(-3)), suggesting that enhanced photo-oxidation together with the rise in temperature promote the formation of OOMs. Most OOMs contained 5 to 10 carbon atoms and 3 to 7 effective oxygen atoms (nO(eff) = nO - 2 x nN). The average nO(eff )increased with increasing atmospheric photo-oxidation capacity, which was the highest in summer and the lowest in winter and autumn. By performing a newly developed workflow, OOMs were classified into the following four types: aromatic OOMs, aliphatic OOMs, isoprene OOMs, and monoterpene OOMs. Among them, aromatic OOMs (29 %-41 %) and aliphatic OOMs (26 %-41 %) were the main contributors in all seasons, indicating that OOMs in Beijing were dominated by anthropogenic sources. The contribution of isoprene OOMs increased significantly in summer (33 %), which is much higher than those in the other three seasons (8 %-10 %). Concentrations of isoprene (0.2-5.3 x 10(7) cm(-3)) and monoterpene (1.1-8.4 x 10(6) cm(-3)) OOMs in Beijing were lower than those reported at other sites, and they possessed lower oxygen and higher nitrogen contents due to high NO, levels (9.5-38.3 ppbv - parts per billion by volume) in Beijing. With regard to the nitrogen content of the two anthropogenic OOMs, aromatic OOMs were mainly composed of CHO and CHON species, while aliphatic OOMs were dominated by CHON and CHON2 ones. Such prominent differences suggest varying formation pathways between these two OOMs. By combining the measurements and an aerosol dynamic model, we estimated that the SOA growth rate through OOM condensation could reach 0.64, 0.61, 0.41, and 0.30 mu g m(-3) h(-1) in autumn, summer, spring, and winter, respectively. Despite the similar concentrations of aromatic and aliphatic OOMs, the former had lower volatilities and, therefore, showed higher contributions (46 %-62 %) to SOA than the latter (14 %-32 %). By contrast, monoterpene OOMs and isoprene OOMs, limited by low abundances or high volatilities, had low contributions of 8 %-12 % and 3 %-5 %, respectively. Overall, our results improve the understanding of the concentration, chemical composition, seasonal variation, and potential atmospheric impacts of OOMs, which can help formulate refined restriction policy specific to SOA control in urban areas.Peer reviewe

Altered spontaneous brain activity during dobutamine challenge in healthy young adults: A resting-state functional magnetic resonance imaging study

IntroductionThere is a growing interest in exploring brain-heart interactions. However, few studies have investigated the brain-heart interactions in healthy populations, especially in healthy young adults. The aim of this study was to explore the association between cardiovascular and spontaneous brain activities during dobutamine infusion in healthy young adults.MethodsForty-eight right-handed healthy participants (43 males and 5 females, range: 22–34 years) underwent vital signs monitoring, cognitive function assessment and brain MRI scans. Cardiovascular function was evaluated using blood pressure and heart rate, while two resting-state functional magnetic resonance imaging (rs-fMRI) methods—regional homogeneity (ReHo) and amplitude of low-frequency fluctuation (ALFF)—were used together to reflect the local neural activity of the brain. Logistic regression was used to model the association between brain and heart.ResultsResults showed that blood pressure and heart rate significantly increased after dobutamine infusion, and the performance in brain functional activity was the decrease in ReHo in the left gyrus rectus and in ALFF in the left frontal superior orbital. The results of logistic regression showed that the difference of diastolic blood pressure (DBP) had significant positive relationship with the degree of change of ReHo, while the difference of systolic blood pressure (SBP) had significant negative impact on the degree of change in ALFF.DiscussionThese findings suggest that the brain-heart interactions exist in healthy young adults under acute cardiovascular alterations, and more attention should be paid to blood pressure changes in young adults and assessment of frontal lobe function to provide them with more effective health protection management

Heterogeneous N2O5 reactions on atmospheric aerosols at four Chinese sites : improving model representation of uptake parameters

Heterogeneous reactivity of N2O5 on aerosols is a critical parameter in assessing NOx fate, nitrate production, and particulate chloride activation. Accurate measurement of its uptake coefficient (gamma N2O5) and representation in air quality models are challenging, especially in the polluted environment. With an in situ aerosol flow-tube system, the gamma N2O5 was directly measured on ambient aerosols at two rural sites in northern and southern China. The results were analyzed together with the gamma N2O5 derived from previous field studies in China to obtain a holistic picture of gamma N2O5 uptake and the influencing factors under various climatic and chemical conditions. The field-derived or measured gamma N2O5 was generally promoted by the aerosol water content and suppressed by particle nitrate. Significant discrepancies were found between the measured gamma N2O5 and that estimated from laboratory-determined parameterizations. An observation-based empirical parameterization was derived in the present work, which better reproduced the mean value and variability of the observed gamma N2O5. Incorporating this new parameterization into a regional air quality model (WRF-CMAQ) has improved the simulation of N2O5, nitrogen oxides, and secondary nitrate in the polluted regions of China.Peer reviewe

Multi-Objective Optimization of the Microchannel Heat Sink Used for Combustor of the Gas Turbine

This research presents a surrogate model and computational fluid dynamic analysis-based multi-objective optimization approach for microchannel heat sinks. The Non-dominated Sorting Genetic Algorithm is suggested to obtain the optimal solution set, and the Kriging model is employed to lower the simulation’s computational cost. The physical model consists of a coolant chamber, a mainstream chamber, and a solid board equipped with staggered Zigzag cooling channels. Five design variables are examined in relation to the geometric characteristics of the microchannel heat sinks: the length of inlet of the cooling channels, the width of the cooling channels, the length of the “zigzag”, the height of the cooling channels, and the periodic spanwise width. The optimal geometry is established by choosing the averaged cooling effectiveness and coolant mass flow rate which enters the mainstream chamber through the microchannel heat sinks as separate objectives. From the Pareto front, the optimal microchannel heat sinks structures are obtained. Three optimized results are studied, including the maximum cooling effectiveness, minimum coolant mass flow rate, and a compromise between the both objectives; a reference case using the median is compared as well. Numerical assessments corresponding to the four cases are performed, and the flow and cooling performance are compared. Furthermore, an analysis is conducted on the mechanisms that impact the ideal geometric parameters for cooling performance

Properties Variation of Carbon Fiber Reinforced Composite for Marine Current Turbine in Seawater

Turbine blade which are generally made of composite is a core device among components of tidal current power generator that converts the flow of tidal current into a turning force. Recent years, damages of composite turbine blades have been reported due to reasons like seawater degradation, lake of strength, manufacture etc. In this paper, water absorption, tensile, bending, longitudinal transverse shearing properties of carbon fiber reinforced plastic (CRP) composite which would be applied to fabricate the marine current turbine blade has been investigated. Furthermore, the variations of properties with seawater immersion period were studied. The results indicated that the water absorption increased almost linearly at the beginning of immersion and then became stable. Tensile strength of specimen tended to decrease firstly and then recovered slightly. However, the longitudinal transverse shearing strength showed reverse variation trend comparing to tensile strength. And the bending property of specimens was depressed significantly. The properties variations in seawater shall be referenced to design and fabrication of composite marine current turbine blade

Characteristics of airborne water-soluble organic carbon (WSOC) at a background site of the North China Plain

Water-soluble organic carbon (WSOC), a significant part of organic carbon (OC) in fine particles, can alter the hygroscopic properties of aerosols and affect global climate change. In this study, PM2.5 filter samples were collected in 2017 winter and summer to investigate the secondary formation, sources and light absorption properties of WSOC. The average WSOC/OC was 66% with the higher value in summer (74%). There are strong correlations between WSOC and secondary components like secondary organic carbon (SOC) and inorganic ions while the correlation between WSOC and EC was weak, indicating secondary formation contributed a dominant portion to WSOC at this site. Moreover, high aerosol liquid water (ALW) and particle acidity were found to enhance the secondary formation of WSOC. The sources of WSOC investigated with Positive Matrix Factorization model (PMF) demonstrated that secondary formation was dominated with 59.9% in winter and 77.9% in summer. The absorption Angstrom exponents (AAE) were 6.88 in winter and 9.15 in summer. The MAE(365) in winter (1.32m(2) g(-1)) was higher than that in summer (0.38m(2) g(-1)), indicating the stronger light absorption ability of WSOC in winter. The radiative forcing of WSOC by light absorption corresponded to only 1-10% of that caused by EC. The potential source contribution function (PSCF) identified inland cities in Shandong province, eastern Henan and Jiangsu province as major source regions of WSOC. The findings from this study imply a critical role of secondary formation characteristics of WSOC at the regional background site of the North China Plain

Dobutamine-induced alternations in cerebral blood flow of healthy adults: a 3D pseudocontinuous arterial spin labeling study

Abstract Background It is unclear whether dobutamine, commonly used clinically in echocardiography and short-term congestive heart failure treatment for promoting increased myocardial contractility, affects brain microcirculatory behavior. Cerebral microcirculation plays an important role in ensuring adequate oxygen transport. Therefore, we investigated the effects of dobutamine on cerebral hemodynamics. Methods Forty-eight healthy volunteers without cardiovascular or cerebrovascular disease underwent MRI to obtain cerebral blood flow (CBF) maps using 3D pseudocontinuous arterial spin labeling before and during the dobutamine stress test. Additionally, cerebrovascular morphology was obtained based on 3D-time-off-light (3D-TOF) magnetic resonance angiography (MRA). Electrocardiogram, heart rate (HR), respiration rate (RR), blood pressure, and blood oxygen were simultaneously recorded before and during dobutamine injection and during recovery (not during MRI). The anatomic features of the circle of Willis and the basilar artery (BA) diameter were assessed on MRA images by two radiologists with extensive neuroimaging experience. Binary logistic regression was used to test for the independent determinants of CBF changes. Results HR, RR, systolic (SBP), and diastolic blood pressure (DBP) significantly increased after dobutamine infusion. Blood oxygen levels remained similar. Compared to the CBF in the resting state, the CBF values exhibited significantly lower CBF levels in both grey matter and white matter. Furthermore, compared with the CBF in the resting state, that in the stress state was decreased in the anterior circulation, mainly in the frontal lobe (voxel level P < 0.001, pixel level P < 0.05). Logistic regression showed that body mass index (BMI; odds ratio [OR] 5.80, 95% confidence interval [CI] 1.60–21.01, P = 0.008], resting SBP (OR 0.64, 95% CI 0.45–0.92, P = 0.014), and BA diameter (OR 11.04, 95% CI 1.05–116.53, P = 0.046) were significantly associated with frontal lobe CBF changes. Conclusions Dobutamine-induced stress significantly decreased CBF in the frontal lobe anterior circulation. Individuals with a high BMI and low SBP during the dobutamine stress test are more likely to have a stress-induced CBF decrease. Thus, attention should be paid to blood pressure, BMI, and cerebrovascular morphology of patients undergoing dobutamine stress echocardiography or those receiving intensive care or anesthesia

Characteristics and formation mechanisms of atmospheric carbonyls in an oilfield region of northern China

Oil and natural gas (O & NG) associated oxygenated volatile organic compounds (OVOCs) have been reported to play a significant role in ozone formation. However, little is known about the characteristics of O & NG-related OVOCs and their environmental impacts in China. In this work, C1-C8 carbonyls, an important member of the OVOCs family, were measured at a rural site and an oilfield in the Yellow River Delta region (YelRD) in winter and summer 2017. The well-defined seasonal (higher in summer) and diurnal variation (peak in the afternoon) patterns of carbonyls indicated a significant influence of secondary formation. Spatially, the measured carbonyls showed higher concentrations in the oilfield than in the rural air due to the strong oilfield emissions of hydrocarbon precursors. The chemical budget and formation mechanisms of formaldehyde and acetaldehyde were explored with the application of an observation-based model coupled with Master Chemical Mechanism. Alkenes (including both anthropogenic and biogenic species) played dominant roles in the secondary formation of formaldehyde both in the oilfield and in the rural area. Seasonally, anthropogenic alkenes showed the highest positive relative incremental reactivity (RIR) for formaldehyde within most winter-cases, while biogenic alkenes showed the highest positive RIR in summer. Spatially, anthropogenic hydrocarbon precursors showed larger RIR values in the oilfield than in the rural area. This study presents for the first-time detailed characteristics of carbonyls in a typical oilfield region of China and quantitatively reveals the impacts of oilfield emissions on the photochemical formation of major carbonyl compounds