Isoprene hydroxy peroxy radicals (ISOPOO), derived from isoprene oxidation by hydroxy radicals (OH), are key intermediates for ozone and secondary organic aerosol (SOA) formation in the atmosphere. Although ISOPOO-water complexes are ubiquitous, their impacts on ISOPOO chemistry remain obscure. Here the previously overlooked water effect on the bimolecular reaction kinetics of ISOPOO was investigated in an oxidative flow reactor. The major first-generation products of ISOPOO, isoprene hydroxy hydroperoxides (ISOPOOH), methacrolein (MACR), and methyl vinyl ketone (MVK), were measured simultaneously at various relative humidity (RH) with the help of a cold trap to avoid potential losses in direct gas sampling. We found that ISOPOO reactions were accelerated significantly under wet conditions, with a greater enhancement on 1,2-ISOPOO than 4,3-ISOPOO. 1,2-ISOPOOH yield appeared faster growth with RH than 4,3-ISOPOOH. MVK yield showed an upward-downward trend with RH, while MACR yield plateaued from 30% RH. To explain the enhancement in the ISOPOOH yield from 3% to 80% RH, the overall rate constants of 1,2-ISOPOO + HO2 and 4,3-ISOPOO + HO2 reactions at 80% RH should be 13 times and twice those at 3% RH, respectively. The empirical formulas were proposed for the first time to parameterize the water effect on ISOPOO + HO2 reactions. The updated kinetics of ISOPOO reactions were incorporated in a box model to simulate the RH-dependent ISOPOOH and C4 carbonyl yields under typical atmospheric conditions. High RH can enhance the ISOPOOH yield in urban, rural, and forest areas, and promote SOA formation correspondingly. Our findings shed light on the critical role of humidity in the reactions of ISOPOO and benefit evaluating the fate of isoprene and its impacts on air quality more accurately in the ambient atmosphere.
Abstract A comprehensive understanding of meteorological, emission and chemical influences on severe haze is essential for air pollution mitigation. However, the nonlinearity of the atmospheric system greatly hinders this understanding. In this study, we developed the quantitative decoupling analysis (QDA) method by applying the Factor Separation (FS) method into the model processes to quantify the effects of emissions (E), meteorology (M), chemical reactions (C), and their nonlinear interactions and impact on fine particulate matter (PM2.5) pollution. Taking a heavy-haze episode in Beijing as an example, we show that different from the integrated process rate (IPR) and the scenario analysis approach (SAA) in previous studies, the QDA method explicitly demonstrate the nonlinear effects by decomposing the variation of PM2.5 concentration into individual contributions of E, M and C terms as well as the contributions from interactions among these processes. Results showed that M dominated the hourly fluctuation of the PM2.5 concentration. The C terms increase with increasing the level of haze, reaching maximum (0.37 μg · \$\mathit\cdot \$ m−3 · \$\mathit\cdot \$ h−1) at the maintenance stage. Moreover, our method reveals that there are non-negligible non-linear effects of meteorological, emission, and chemical processes during pollution stage, with the mean accounting for 50% of the increase in PM2.5 concentrations, which is often ignored in the current air pollution control strategies. This study highlights that the QDA approach can be used to gain insight into the formation of heavy pollution, and to identify uncertainty in numerical models.
What promotes female empowerment and gender equality? We investigate how internal population mobility and social interaction foster the advancement of female empowerment and gender equality across diverse subpopulations. Using the urban-to-rural youth resettlement program in China during the 1970s — the Send-down Movement — as our empirical context, we find that rural females with greater exposure to urban youths have achieved higher levels of education, increased labor force participation, greater financial independence, enhanced autonomy in marital and fertility decisions, increased political engagement, heightened self-confidence, reduced risk aversion, and a stronger belief in gender-equal ideologies and social values. Our findings underscore the role of population mobility in disseminating gender-equal ideologies and practices, both through human capital formation and social interactions, leading to lasting impacts on female empowerment in traditional societies.
In this study, the chemical mechanisms of O3 and nitrate formation as well as the control strategy were investigated based on extensive observations in Tai'an city in the NCP and an observation-constrained box model. The results showed that O3 pollution was severe with the maximum hourly O3 concentration reaching 150 ppb. Higher O3 concentration was typically accompanied by higher PM2.5 concentrations, which could be ascribed to the common precursors of VOCs and NOx. The modeled averaged peak concentrations of OH, HO2, and RO2 were relatively higher compared to previous observations, indicating strong atmospheric oxidation capacity in the study area. The ROx production rate increased from 2.8 ppb h−1 to 5 ppb h−1 from the clean case to the heavily polluted case and was dominated by HONO photolysis, followed by HCHO photolysis. The contribution of radical-self combination to radical termination gradually exceeded NO2 + OH from clean to polluted cases, indicating that O3 formation shifted to a more NOx-limited regime. The O3 production rate increased from 14 ppb h−1 to 22 ppb h−1 from clean to heavily polluted cases. The relative incremental reactivity (RIR) results showed that VOCs and NOx had comparable RIR values during most days, which suggested that decreasing VOCs or NOx was both effective in alleviating O3 pollution. In addition, HCHO, with the largest RIR value, made important contribution to O3 production. The Empirical Kinetic Modeling Approach (EKMA) revealed that synergistic control of O3 and nitrate can be achieved by decreasing both NOx and VOCs emissions (e.g., alkenes) with the ratio of 3:1. This study emphasized the importance of NOx abatement for the synergistic control of O3 and nitrate pollution in the Tai'an area as the sustained emissions control has shifted the O3 and nitrate formation to a more NOx-limited regime.
Bacterial community is strongly associated with activated sludge performance, but there still remains a knowledge gap regarding the rare bacterial community assembly and their influence on the system performance in industrial wastewater treatment plants (IWWTPs). Here, we investigated bacterial communities in 11 full-scale IWWTPs with similar process designs, aiming to uncover ecological processes and functional traits regulating abundant and rare communities. Our findings indicated that abundant bacterial community assembly was governed by stochastic processes; thereby, abundant taxa are generally present in wastewater treatment compartments across different industrial types. On the contrary, rare bacterial taxa were primarily driven by deterministic processes (homogeneous selection 61.9%-79.7%), thus they only exited in specific IWWTPs compartments and wastewater types. The co-occurrence networks analysis showed that the majority of keystone taxa were rare bacterial taxa, with rare taxa contributing more to network stability. Furthermore, rare bacteria rather than abundant bacteria in the oxic compartment contributed more to the degradation of xenobiotics compounds, and they were main potential drivers of pollutant removal. This study demonstrated the irreplaceable roles of rare bacterial taxa in maintaining system performance of IWWTPs, and called for environmental engineers and microbial ecologists to increase their attention on rare biosphere.
Biotransformation of ferrihydrite (Fh) by dissimilatory iron-reducing bacteria (DIRB) into various secondary minerals assemblages widely occurs in anaerobic environments. While respiration-driven supply rates of Fe(II) have been proposed as a primary factor controlling kinetics and mineral products of this process, the specific mechanism by which DIRB respiration rates regulate Fh biotransformation remains elusive. Here, to minimize the complex effects of microbial cells, we conducted Fh transformation using 1 mM biogenic Fe(II) (BioFe(II)), added at different rates to mimic diverse respiration-driven supply rates of Fe(II) by DIRB. For comparison, transformation experiments with FeSO4 alone and FeSO4 plus citrate (CitFe(II)) added at the corresponding supply rates were performed to decouple the specific effects of Fe(II) addition rates and extracellular polymeric substances (EPS) associated with BioFe(II). Decreasing FeSO4 supply rates favored the transformation of Fh to lepidocrocite (Lp) over to Gt and the subsequent transformation of Lp to magnetite (Mt), altering the transformation pathway from Fh → Lp/Gt → Gt to Fh → Lp/Gt → Mt/Gt. These results underscore the significant effect of aqueous Fe(II) supply rates on the competition of olation and oxolation of labile Fe(III) intermediates into different secondary minerals. In the experiments with BioFe(II) and CitFe(II), although EPS or citrate slightly increased Fe(II) adsorption and Fe(III)labile generation, the increase in sorbed Fe(II) was minimal compared to the variations in aqueous Fe(II) concentrations caused by the different Fe(II) supply rates. At the same Fe(II) supply rates, EPS or citrate notably inhibited the transformation of Fh to Gt and the further conversion of Lp, altering the pathway from Fh → Mt/Gt/Lp to primarily Fh → Lp. These effects became more pronounced with the decrease of BioFe(II) and CitFe(II) supply rates. Our findings provide new insights into how DIRB respiration rates control kinetics, pathways, and mineral products of Fh transformation, which is crucial for elucidating the relevant biogeochemical cycling of nutrients and (im)mobilization of contaminants.