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Recently, many researchers focus on Na-ion batteries as an alternative to Li-ion batteries, owing to their low cost and high natural abundance. However, they suffer from low electrochemical performance and large volume expansion, which makes difficult to industrial application. Therefore, various strategies have been proposed to address the current issues, such as particle-size control, surface-coating, and application of electrode material with various crystal structures. Herein, we briefly introduce and discuss the recent research with development trend of cathode material for Na-ion batteries.

The UNIfied Partitioning-Aerosol phase Reaction (UNIPAR) model was established on the Comprehensive Air quality Model with extensions (CAMx) to process Secondary Organic Aerosol (SOA) formation by capturing multiphase reactions of hydrocarbons (HCs) in regional scales. SOA growth was simulated using a wide range of anthropogenic HCs including ten aromatics and linear alkanes with different carbon-lengths. The atmospheric processes of biogenic HCs (isoprene, terpenes, and sesquiterpene) were simulated for the major oxidation paths (ozone, OH radicals, and nitrate radicals) to predict day and night SOA formation. The UNIPAR model streamlined the multiphase partitioning of the lumping species originating from semi-explicitly predicted gas products and their heterogeneous chemistry to form non-volatile oligomeric species in both organic aerosol and inorganic aqueous phase. The CAMx-UNIPAR model predicted SOA formation at four ground urban sites (San Jose, Sacramento, Fresno, and Bakersfield) in California, United States during wintertime 2018. Overall, the simulated mass concentrations of the total organic matter, consisting of primary OA (POA) and SOA, showed a good agreement with the observations. The simulated SOA mass in the urban areas of California was predominated by alkane and terpene. During the daytime, low-volatile products originating from the autoxidation of long-chain alkanes considerably contributed to the SOA mass. In contrast, a significant amount of nighttime SOA was produced by the reaction of terpene with ozone or nitrate radicals. The spatial distributions of anthropogenic SOA associated with aromatic and alkane HCs were noticeably affected by the southward wind direction owing to the relatively long lifetime of their atmospheric oxidation, whereas those of biogenic SOA were nearly insensitive to wind direction. During wintertime 2018, the impact of inorganic aerosol hygroscopicity on the total SOA budget was not evident because of the small contribution of aromatic and isoprene products that are hydrophilic and reactive in the inorganic aqueous phase. However, an increased isoprene SOA mass was predicted during the wet periods, although its contribution to the total SOA was little.

The atmospheric mineral aerosol reaction (AMAR) model, which was developed to simulate dust-driven heterogeneous chemistry of SO2 and NOx, was combined with the comprehensive air quality model with...

Rapid sulfate formation is recognized as a key characteristic of severe winter haze in China. However, air quality models tend to underestimate sulfate formation during heavy haze periods, and heterogeneous formation pathways have been proposed as promising mechanisms to reduce gaps between observation and model simulation. In this study, we implemented a reactive SO2 uptake mechanism through the SO2+NO2 heterogeneous reactions in the Comprehensive Air Quality Model with Extensions (CAMx) to improve simulation of sulfate formation in the Yangtze River Delta (YRD) region. Parameterization of the SO2+NO2 heterogeneous reactions is based on observations in Beijing and considered both the impact of relative humidity and aerosol pH on sulfate formation. Ammonia is reported to be critical for the formation of secondary inorganic aerosols. Estimation of ammonia emissions is usually associated with large uncertainties and models tend to underestimate ammonia concentrations substantially. Sensitivity tests were conducted to evaluate the influence of the SO2+NO2 heterogeneous reactions as well as ammonia emissions on modeled sulfate concentrations during a period with several heavy haze episodes in the YRD region. Base case model results show large underestimation of sulfate concentrations by 36 % under polluted conditions in the YRD region. Adding the SO2+NO2 heterogeneous reactions or doubling ammonia emissions alone leads to slight model improvement ( ∼6 %) on simulated sulfate concentrations in the YRD region. However, model performance significantly improved when both the SO2+NO2 heterogeneous reactions and doubled ammonia emissions were included in the simulation: predicted sulfate concentrations during polluted periods increased from 23.1 µ g m −3 in the base scenario to 29.1 µ g m −3 (representing an increase of 26 %). Aerosol pH is crucial for the SO2+NO2 heterogeneous reactions, and our calculated aerosol pH is always acidic and increased by 0.7 with doubled ammonia emissions. Modeling results also show that this reactive SO2 uptake mechanism enhanced sulfate simulations by 1 to 5 µ g m −3 for the majority of the eastern and central parts of China, with more than 20 µ g m −3 increase in sulfate concentrations over the northeastern plain. These findings suggest that the SO2+NO2 heterogeneous reactions could be potentially important for sulfate formation in the YRD region as well as other parts of China. Further studies are needed to constrain the uncertainties associated with the parameterization of the SO2+NO2 heterogeneous reactions based on local data as well as to evaluate this mechanism in other regions. In addition, ammonia emissions were found to be a key driving variable of the spatial patterns of sulfate enhancement due to the new pathway. Substantial efforts are needed to improve the accuracy of the ammonia emission inventory.

Formation of organic aerosol (OA) and ozone were simulated for the greater Houston area in September 2013 and 2028 (summer conditions) using the Comprehensive Air Quality Model with Extensions (CAMx). We also simulated the background concentrations in the absence of US anthropogenic emissions. The 1.5-dimensional volatility basis set scheme was used to represent formation of primary and secondary OA (POA and SOA). The path-integral method for source apportionment was successfully extended to OA formation using the same numerical approach previously used for ozone and then applied to apportion the anthropogenic increment of OA and ozone to six emission source categories. The anthropogenic increment is the difference between the 2013 or 2028 simulation and the background simulation. Averaged over 21 air monitoring sites in Houston, point sources make the largest contribution to monthly average SOA and OA (25%–37%, depending on year) and to monthly maximum 8-h ozone (21%–26%). Onroad and then nonroad sources are the next most important in 2013, but their contributions diminish by 2028. The sources’ contributions to SOA correlate much more strongly with their NOx emissions than with their emissions of organic precursor species. Anthropogenic emissions enhance OA formation from biogenic emissions, and this enhancement is 46% and 48% of the total OA concentration in Houston in 2013 and 2028, respectively. Point sources make the largest contribution to the enhancement. Additional results for a larger regional area covering Texas and nearby states are also presented.

Activated carbon (AC) is an inexpensive catalyst for oxygen reduction in an air cathode of microbial fuel cells (MFCs). In the AC-based cathode, carbon black (CB) is used as a conductive supporting material. In this study, it was hypothesized cathodic performance would increase if reduced graphene oxide (rGO) replaces CB in an optimum ratio. rGO replaced CB in the four different weight ratios of rGO toCB: 0:30 (rGO0); 5:25 (rGO5); 15:15 (rGO15); 30:0 (rGO30). Maximum power density was the best in rGO15 (2642 mW/m2) followed by rGO5 (2142 mW/m2). In the optimum external resistance operation, rGO5 and rGO15 showed similar power (∼1060 mW/m2), higher than the others. Linear sweep voltammetry, cyclic voltammetry, and impedance spectroscopy also showed that the optimal rGO additions improved cathodic performance and reduced cathodic internal resistance. Due to the flatter and wider shape of rGO and 5 times higher electrical conductivity than CB, the rGO addition improved the cathodic performance, but the complete replacement of CB with rGO decreased the cathodic performance due to the increased thickness and the morphological crack. The optimum rGO addition is a simple and effective method for improving cathodic performance.

A three-dimensional chemical transport model, PMCAMx, was used to quantify the contribution of biomass burning organic aerosol (bbOA) to total organic aerosol (OA) concentrations in the continental U.S. Simulations were performed during three seasonally-representative months (April, July, and September 2008). Biomass burning is predicted to contribute 9% of the domain-averaged OA in April, 28% in July and 13% in September. Secondary OA from semivolatile and intermediate volatility organic compounds is the largest contributor to bbOA concentrations for all months simulated, followed by fresh primary OA. PMCAMx bbOA predictions using the Volatility Basis Set were compared to the results of CAMx version 6.10 that assumes that bbOA is nonvolatile and inert. PMCAMx predicts 66%, 113%, and 108% higher average concentration values of bbOA for April, July, and September, respectively. Predicted OA concentrations at biomass-impacted sites were compared to observed values from the STN and IMPROVE networks. The treatment of biomass burning emissions as semivolatile and reactive improved model performance during the spring and summer. During the fall both models overpredicted the OA levels, suggesting that the fire emissions may have been overestimated. In this case the additional SOA produced in PMCAMx resulted in worse performance.

Carbon-based material is commonly used for anodes in MFCs, but its low conductivity often limits anodic performance. Application of corrosion-resistive current collector to carbon-based anode can be a promising strategy for increasing the anodic performance. In this study, it was hypothesized increasing metal current collector improved anodic performance. Two different carbon-felt anodes with titanium wires (CF-W) or stainless steel mesh (CF-M) as a current collector were tested in a single chamber MFC. In the short-term tests such as polarization and impedance tests, CF-M with the larger current collector area (21.7 cm2) had 33% higher maximum power (2311 mW/m2), 81% lower anodic resistance (3 Ω), and 92% lower anodic impedance (1.1 Ω). However, in the long-term tests, CF-W with the smaller current collector area (0.6 cm2) showed higher performance in power and current generation, COD removal, and CE (51%, 10%, 11%, and 5% higher, respectively) and produced 41% higher net current in cyclic voltagramm (20.0 mA vs. 14.2 mA). This result shows that larger current collector is advantageous in short-term performance and disadvantageous in long-term performance, because the larger current collector is good for current collection, but interferes with mass transfer and microbial growth.

Electrode is a key component in a microbial electrolysis cell (MEC) and it needs significant improvement for practical implementation of MEC. For effective development of electrode technology, accurate and reproducible analytical methods are very important. Linear sweep voltammetry (LSV) is an essential analytical method for evaluating electrode performance; however, it has not been firmly established yet in the MEC field. In this study, biological brush (BB), abiotic brush (AB), Pt wire (PtW), stainless steel wire (SSW) and mesh (SSM)) were tested to explore the most suitable counter electrode in different medium conditions. Coefficient of variation (CV) for Imax of LSV were comparatively analyzed. In BB-anode LSV, SSW (0.48%) and SSM (2.17%) showed higher reproducibility as a counter electrode. In SSM-cathode LSV, BB (1.76%) and PtW (2.01%) produced more reproducible results. In the Ni-AC-SSM-cathode LSV, PtW (3.54%) and BB (8.81%) produced more reproducible result. It shows electrode used in the operation is an appropriate counter electrode in the acetate-added condition. However, in the absence of acetate, PtW (1.24%) and BB (1.71%) produced more reproducible results in SSM cathode and PtW (0.61%) and SSW (1.21%) did in the Ni-AC-SSM-cathode, showing PtW is an appropriate counter electrode. These results also shows that PtW is an appropriate counter electrode in cathode LSV.

To obtain an accurate and reproducible experimental results in microbial fuel cell (MFC), it is important to know ‘anode maturation biofilm’ to produce a stable and maximum performance. For this purpose, four single chamber MFCs were tested in this study. The linear sweep voltammetry (LSV) polarization tests illustrated that maximum power densities of three MFCs became stable after 9 weeks. Although there were variations afterwards, such variations were negligible. Average maximum power densities from the 9th to the 17th week were 2,990 mW/m2 (MFC-4), 2,983 mW/m2 (MFC-2), 2,368 mW/m2 (MFC-3) and 837 mW/m2 (MFC-1). Polarization resistance shows that MFC-1 had much larger anode resistance (36.6-85.4 Ω) than the other MFCs (1.7-11.6 Ω). Anodic cyclic voltammetry (CV) shows that current production increased over time and MFC-1 had much smaller current production (24.4 mA) than the other MFCs (31.0-34.9 mA) at 17th week. The increased current production indicates anode biofilm became more mature over time, but overall cell performance did not increased accordingly. Possibly due to the bad inoculation, MFC-1 showed the lowest performance. However, its performance was restored to the initial performance and anode resistance was reduced by 47% at 17th week. This study shows that the optimum anode maturation time is 9 weeks and that bioanode performance is a key factor for MFC performance. This study also shows than LSV polarization and CV tests are accurate and non-destructive measurement methods for diagnosing anode performance.

The Comprehensive Air quality Model with extensions (CAMx) has been employing ISORROPIA for inorganic aerosol thermodynamic calculations. Recently, the Equilibrium Simplified Aerosol Model (EQSAM) was added to CAMx as an alternative to ISORROPIA for computing concentrations of the inorganic ions: sulfate, nitrate, ammonium, sodium and chloride. By design, EQSAM has more streamlined algorithms than ISORROPIA, which may lead to different model concentrations and faster run times. We apply CAMx using both thermodynamic equilibrium modules for simulations of the continental US with 12 km grid resolution for winter and summer months. Model predictions of inorganic ions by both algorithms are compared and model performance is evaluated against ambient data collected by speciated PM monitoring networks. The overall model run times are also compared. Our purpose is to introduce EQSAM as a newly available option in CAMx and provide information relevant to choosing between the two available aerosol thermodynamics modules in CAMx taking into consideration the scheme’s performance attributes as well as the requirements of each model application.

Activated carbon (AC) is an inexpensive catalyst for the oxygen reduction reaction in the air cathode of microbial fuel cells (MFCs). However, since the electrochemical catalytic activity of AC is poor, it is necessary to improve its performance. The metal–organic framework (MOF) is composed of a metal ion and an organic linker. It has high porosity and high electrochemical catalytic activity. Herein, ZIF-67 (cobalt-nitrogen framework) was combined with activated carbon through ultrasonication (U) and solution precipitation (H), which was used to make ZIF-67U and ZIF-67H cathodes, respectively. In maximum power density, ZIF-67U cathode produced 4203 mW m−2, and ZIF-67H did 3881 mW m−2, which is 60% and 48% higher than AC cathode (2625 mW m−2) and 160% and 140% higher than Pt cathode (1614 mW m−2), respectively. Cobalt and nitrogen contents increased in the ZIF catalysts. In atomic nitrogen contents of catalyst surface, pyridine-N was 28% in ZIF-67U and 38% in ZIF-67H, respectively; pyrrole-N was 56% in ZIF-67U and 25% in ZIF-67H, respectively; no nitrogen was detected in AC. These cobalt-nitrogen increased the active site of the oxygen reduction reaction (ORR), improved the reaction rate, and decreased charge transfer impedance. Impedance analysis demonstrated the ZIF-67 addition also decreased the diffusion impedance possibly due to the improved cathode porosity. AC and ZIF-67 were bonded using ultrasonication and tested in the MFC for the first time, producing the highest power ever among the MOFs in the 50-mM phosphate-buffer-saline condition so far.

Differences between two air quality modeling systems reveal important uncertainties in model representations of secondary organic aerosol (SOA) fate. Two commonly applied models (CMAQ: Community Multiscale Air Quality; CAMx: Comprehensive Air Quality Model with extensions) predict very different OA concentrations over the eastern U.S., even when using the same source data for emissions and meteorology and the same SOA modeling approach. Both models include an option to output a detailed accounting of how each model process (e.g., chemistry, deposition, etc.) alters the mass of each modeled species, referred to as process analysis. We therefore perform a detailed diagnostic evaluation to quantify simulated tendencies (Gg/hr) of each modeled process affecting both the total model burden (Gg) of semi-volatile organic compounds (SVOC) in the gas (g) and aerosol (a) phases and the vertical structures to identify causes of concentration differences between the two models. Large differences in deposition (CMAQ: 69.2 Gg/d; CAMx: 46.5 Gg/d) contribute to significant OA bias in CMAQ relative to daily averaged ambient concentration measurements. CMAQ's larger deposition results from faster daily average deposition velocities (VD) for both SVOC (g) (VD,cmaq = 2.15 × VD,camx) and aerosols (VD,cmaq = 4.43 × Vd,camx). Higher aerosol deposition velocity would be expected to cause similar biases for inert compounds like elemental carbon (EC), but this was not seen. Daytime low-biases in EC were also simulated in CMAQ as expected but were offset by nighttime high-biases. Nighttime high-biases were a result of overly shallow mixing in CMAQ leading to a higher fraction of EC total atmospheric mass in the first layer (CAMx: 5.1–6.4%; CMAQ: 5.6–6.9%). Because of the opposing daytime and nighttime biases, the apparent daily average bias for EC is reduced. For OA, there are two effects of reduced vertical mixing: SOA and SVOC are concentrated near the surface, but SOA yields are reduced near the surface by nighttime enhancement of NOx. These results help to characterize model processes in the context of SOA and provide guidance for model improvement.

Various materials and anode structures have been applied to enhance MFC performance. However, their comparative evaluation of performance and electrochemistry has not yet been investigated in detail under a same condition. In this study, a carbon-cloth anode, an anode-cathode assembly, and a brush anode with two different orientations were tested under a same condition for comparative analyses on their performance and electrochemistry, in order to reveal their unique electrochemical characteristics. The brush anode cells exhibited better performance than the carbon cloth cells. The brush anodes showed 41–72% higher maximum power densities, 18–75% higher maximum current density and 24–32% higher optimum current densities than the carbon cloth anodes. The brush anodes showed 25–43 Ω lower anodic polarization resistance than the carbon cloth anodes. The brush anodes showed 1.6–21.2 Ω lower ohmic impedance, 7.7–10.6 Ω lower charge transfer impedance and 9.3–31.8 Ω lower anodic impedance than the carbon cloth anodes. Anodic ohmic impedance was greatest in the carbon-cloth-anode MFC (21.9 Ω), where loose contact between a carbon cloth and a current collector might cause the high ohmic resistance, and large solution resistance in the cell could diminish anode performance due to slow ion transport. In order to improve MFC performance by modifying anode structures, we suggest the followings: 1) an anode should have large surface area, 2) anodic carbon material and a metal current collector must be tightly connected, 3) locating a brush anode closer to a cathode can be important.

The Goddard Earth Observing System global chemical transport (GEOS-Chem) model was used at 2° × 2.5° resolution to simulate ozone formation for a base case representing year 2010 and a natural background case without worldwide anthropogenic emissions. These simulations provided boundary concentrations for base and natural background simulations with the Comprehensive Air Quality Model with Extensions (CAMx) on a North American domain (one-way nested) at 12 km × 12 km resolution over March–September 2010. The predicted maximum daily average 8 h (MDA8) background ozone for the US is largest in the mountainous areas of Colorado, New Mexico, Arizona, and California. The background MDA8 ozone in some of these locations exceeds 60 ppb, when averaged over the 10 days with the largest base-case ozone (T10base average). The background ozone generally becomes both a larger fraction of the base-case ozone in the western US and a smaller fraction in the eastern US when proceeding from spring to summer to the T10base average. The ozone difference between the base and background cases represents the increment to ozone from all anthropogenic sources. The path-integral method was applied to allocate this anthropogenic ozone increment to US anthropogenic emissions, Canadian/Mexican anthropogenic emissions, and the anthropogenic components of the lateral and top boundary concentrations (BCs). Using the T10base average MDA8 ozone, the relative importance of the sources is generally US emissions > anthropogenic lateral BCs > Canadian/Mexican emissions ≫ anthropogenic top BCs. Specifically, for 10 US urban areas, the source contributions were 12–53 ppb for US emissions, 3–9 ppb for lateral BCs, 0.2–3 ppb for Canadian/Mexican emissions, and ≤ 0.1 ppb for top BCs. The contributions of the lateral BCs are largest for the higher-elevation US sites in the Intermountain West and along the western boundary of the domain. In Denver, for example, the lateral BCs contribute 44 % to the T10base anthropogenic increment. Averaging over the 10 days in the background case with the largest MDA8 ozone (T10bkgd), the contribution from US emissions is reduced to 3–13 ppb at the 10 urban sites, leading to a reduction in the anthropogenic ozone increment. The contribution of the Canadian/Mexican emissions remains about the same (0.3–2 ppb), and the contribution from the lateral BCs increases (5–10 ppb), especially at the lower-elevation urban sites. The net effect at the urban sites is that the relative importance of the anthropogenic lateral BCs is significantly greater for the T10bkgd average than the T10base average. This is also true for rural sites studied, where the anthropogenic lateral BC contribution becomes as large as 68 % of the anthropogenic increment for the T10bkgd average. In addition to the source apportionment, we also used surface and ozonesonde measurements to evaluate GEOS-Chem and CAMx performance.

Microbial electrolysis cell (MEC) is an innovative electrochemical technology that decomposes organic matter in anode and produces hydrogen in cathode. It is imperative to use a high-performance and a low-cost cathode material to make the application of MEC economically viable. In this study, five different cathodes made of low-cost materials were tested in MECs. The materials included activated carbon (AC) and nickel powder (Ni) as a cathode catalyst; polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) as a catalyst binder; stainless steel mesh (SSM) as a cathode substrate or a cathode itself. Among the tested cathodes, Ni/AC/PTFE obtained the best performance, followed by Ni/AC/PVDF, AC/PVDF, flamed-oxidized SSM (SSM/F) and SSM. Ni/AC/PTFE exhibited the best performance in hydrogen production rate (HPR, 1.88 L/L d), hydrogen purity (97.5%), coulombic efficiency (124%), energy efficiency (216%), cathodic capacitance (0.9924 F), along with the lowest cathodic impedance (35 Ω). The worst performed SSM showed as follows: 0.57 L/L d of HPR, 71% of hydrogen purity, 36% of coulombic efficiency, 62% of energy efficiency, 0.0008 F of cathodic capacitance and 62 Ω of cathodic impedance. This study shows quantitatively the electrochemical and performance transitions of MEC according to the cathode component changes.

Ozone formation in California in year 2017 was simulated using three chemical mechanisms: the Statewide Air Pollution Research Center 2007 mechanism with updated toxics and isoprene chemistry (S07TIC); the Carbon Bond 6, revision 2 (CB6r2) mechanism; a modified CB6r2 mechanism with increased hydroxyl radical (OH) production from isoprene oxidation at low nitrogen oxide (NOx) concentrations (CB6r2OH). The simulations with a photochemical grid model (PGM) showed little difference in ozone between CB6r2 and CB6r2OH. Further analysis with a box model found little sensitivity of ozone to OH production in the isoprene chemistry of all three mechanisms under conditions representative of California. The S07TIC generally predicts greater ozone than the CB6r2, and the difference in the predicted concentrations exceeds the uncertainty estimated from uncertainties in the emissions inventory. The sensitivity of ozone to anthropogenic volatile organic compound (VOC), NOx and carbon monoxide (CO) emissions and to isoprene emissions was also calculated with the PGM. Accounting for uncertainties in the emissions inventory, the sensitivity to NOx emissions is significantly different between S07TIC and CB6r2 in central and northern California; the sensitivity to isoprene emissions is significantly different in southern California. All mechanisms give a negative sensitivity of ozone to isoprene emissions in areas of northern California where NOx emissions are small. The CB6r2 and S07TIC differ in the sensitivity of ozone to organic nitrate (ON) formation from isoprene oxidation, likely because all ONs recycle to NOx in the S07TIC mechanism but only first-generation ONs do so in the CB6r2. For current California conditions, uncertainties in OH production from isoprene have little impact on ozone, but the extent to which isoprene ONs recycle NOx does impact ozone concentration and ozone sensitivity to NOx emissions.

Rapid sulfate formation is recognized as key characteristics of severe winter haze in China. However, air quality models tend to underestimate sulfate formation during heavy haze periods and heterogeneous formation pathways have been proposed as promising mechanisms to reduce gaps between observation and model simulation. In this study, we implemented a reactive SO2 uptake mechanism through the SO2+NO2 heterogeneous reactions in the Comprehensive Air Quality Model with extensions (CAMx) to improve simulation of sulfate formation in the Yangtze River Delta (YRD) region for the first time. Parameterization of the SO2+NO2 heterogeneous reactions is based on observations in Beijing and considered both impact of relative humidity and aerosol pH on sulfate formation. Ammonia is reported to be critical for the formation of secondary inorganic aerosols and estimation of ammonia emissions is usually associated with large uncertainties. Sensitivity tests were conducted to evaluate the importance of the SO2+NO2 heterogeneous reactions as well as ammonia emissions on modelled sulfate concentrations during a period with several heavy haze episodes in the YRD region. Base case model results show large underestimation of sulfate concentrations by 36 % under polluted conditions in the YRD region. Adding the SO2+NO2 heterogeneous reactions or doubling ammonia emissions alone leads to slight model improvement (~ 6 %) on simulated sulfate concentrations in the YRD region. However, model performance significantly improved when both the SO2+NO2 heterogeneous reactions and doubled ammonia emissions were included in the simulation: predicted sulfate concentrations during polluted periods increased from 23.1 µg m−3 in the base scenario to 29.1 µg m−3 (representing an increase of 26 %). Aerosol pH is crucial for the SO2+NO2 heterogeneous reactions and our calculated aerosol pH is always acidic and increased by 0.7 with doubled ammonia emissions. Modelling results also show that this reactive SO2 uptake mechanism enhanced sulfate simulations by 1 to 5 µg m−3 for the majority of eastern and central part of China, with more than 20 µg m−3 increase of sulfate concentrations over the north-eastern plateau. These findings suggest that the SO2+NO2 heterogeneous reactions could be important for sulfate formation in the YRD region as well as other parts of China. In addition, ammonia emissions need to be carefully estimated. More studies are needed to improve the parameterization of the SO2+NO2 heterogeneous reactions based on local data further evaluate this mechanism in other regions. Substantial efforts are needed to improve the accuracy of ammonia emissions inventory.

The Environmental Benefits Mapping and Analysis Program (BenMAP) is used by the US Environmental Protection Agency (EPA) in regulatory impact and risk assessments. We used BenMAP to estimate the he...

A three-dimensional chemical transport model, PMCAMx-SR, was applied in the continental U.S. to investigate the contribution of prescribed burning and other biomass burning sources to the total organic aerosol (OA) concentrations. Simulations were performed during three seasonally-representative months (April, July and September 2008). Prescribed biomass burning organic aerosol (bbOA) emission rates were estimated to be approximately 300, 80 and 250 tn d−1 during April, July and September respectively. Prescribed burning was limited during July due to the prevailing weather conditions. Prescribed burning is responsible for 45% of the total bbOA emissions during the simulated spring period, 20% during the fall, and just 3% during the summer. The predicted maximum hourly prescribed bbOA concentration reached approximately 100 μg m−3 during April in South Carolina and during September in New Mexico, whereas it was less than 15 μg m−3 during July in Arkansas. The average contribution of prescribed burning to OA in the continental U.S. is quite low (less than 5%) and 60–70% is predicted to be secondary OA. Biomass burning secondary organic aerosol (bbSOA) levels far away from the prescribed fires are predicted to exceed 2 μg m−3. In states with intensive prescribed burning activities this source is predicted to contribute 20–40% of the OA on a monthly average basis. In these states (for example South Carolina during April), the predictions reveal that people can be exposed for 20 h per month on average to bbOA levels exceeding 5 μg m−3 and for 200 h to levels above 0.5 μg m−3. This should be contrasted to 220 h of exposure to bbOA above 5 μg m−3 and 650 h to bbOA above 0.5 μg m−3 for states and periods with intense wild fires (for example California during July).

Community Multiscale Air Quality (CMAQ) model simulations utilizing the traditional organic aerosol (OA) treatment (CMAQ-AE6) and a volatility basis set (VBS) treatment for OA (CMAQ-VBS) were evaluated against measurements collected at routine monitoring networks (Chemical Speciation Network (CSN) and Interagency Monitoring of Protected Visual Environments (IMPROVE)) and those collected during the 2010 California at the Nexus of Air Quality and Climate Change (CalNex) field campaign to examine important sources of OA in southern California. Traditionally, CMAQ treats primary organic aerosol (POA) as nonvolatile and uses a two-product framework to represent secondary organic aerosol (SOA) formation. CMAQ-VBS instead treats POA as semivolatile and lumps OA using volatility bins spaced an order of magnitude apart. The CMAQ-VBS approach underpredicted organic carbon (OC) at IMPROVE and CSN sites to a greater degree than CMAQ-AE6 due to the semivolatile POA treatment. However, comparisons to aerosol mass spectrometer (AMS) measurements collected at Pasadena, CA, indicated that CMAQ-VBS better represented the diurnal profile and primary/secondary split of OA. CMAQ-VBS SOA underpredicted the average measured AMS oxygenated organic aerosol (OOA, a surrogate for SOA) concentration by a factor of 5.2, representing a considerable improvement to CMAQ-AE6 SOA predictions (factor of 24 lower than AMS). We use two new methods, one based on species ratios (SOA/ΔCO and SOA/Ox) and another on a simplified SOA parameterization, to apportion the SOA underprediction for CMAQ-VBS to slow photochemical oxidation (estimated as 1.5 × lower than observed at Pasadena using −log(NOx : NOy)), low intrinsic SOA formation efficiency (low by 1.6 to 2 × for Pasadena), and low emissions or excessive dispersion for the Pasadena site (estimated to be 1.6 to 2.3 × too low/excessive). The first and third factors are common to CMAQ-AE6, while the intrinsic SOA formation efficiency for that model is estimated to be too low by about 7 × . From source-apportioned model results, we found most of the CMAQ-VBS modeled POA at the Pasadena CalNex site was attributable to meat cooking emissions (48 %, consistent with a substantial fraction of cooking OA in the observations). This is compared to 18 % from gasoline vehicle emissions, 13 % from biomass burning (in the form of residential wood combustion), and 8 % from diesel vehicle emissions. All "other" inventoried emission sources (e.g., industrial, point, and area sources) comprised the final 13 %. The CMAQ-VBS semivolatile POA treatment underpredicted AMS hydrocarbon-like OA (HOA) + cooking-influenced OA (CIOA) at Pasadena by a factor of 1.8 compared to a factor of 1.4 overprediction of POA in CMAQ-AE6, but it did capture the AMS diurnal profile of HOA and CIOA well, with the exception of the midday peak. Overall, the CMAQ-VBS with its semivolatile treatment of POA, SOA from intermediate volatility organic compounds (IVOCs), and aging of SOA improves SOA model performance (though SOA formation efficiency is still 1.6–2 × too low). However, continued efforts are needed to better understand assumptions in the parameterization (e.g., SOA aging) and provide additional certainty to how best to apply existing emission inventories in a framework that treats POA as semivolatile, which currently degrades existing model performance at routine monitoring networks. The VBS and other approaches (e.g., AE6) require additional work to appropriately incorporate IVOC emissions and subsequent SOA formation.

It is critical to evaluate an air quality model prior to regulatory applications to ensure model performance is adequate for regulatory decision making. However, no formal benchmarks currently exist in the United States (US) to judge whether a model's performance is acceptable for given purposes, and practitioners usually rely on criteria established in the past, when the extent of modeling domains and length of simulation periods were relatively limited. This study conducts modeling experiments to investigate the impact of using different modeling configurations on various policy-related modeling outcomes. Two widely used chemical transport models with different meteorological data, biogenic emissions, and aerosol modeling schemes are applied to an annual modeling period, and model performance for ozone and particulate matter (PM) constituents is evaluated for different timescales and geographical regions in the US. Results show that while both models can be considered acceptable based on criteria commonly used by modelers when evaluated on the annual basis, the model performance at finer levels can reveal differences between the two modeling configurations, which may lead to different policy outcomes. Model results for 2005 and 2014 are used to determine monitoring sites projected to violate current US standards for ozone and fine PM, sites significantly affected by emissions from two selected upwind states, and ratios of deposition to ambient concentration of oxides of sulfur and nitrogen, a.k.a. transference ratios, at each monitoring site in the eastern US. The two modeling configurations result in quite different lists of sites and transference ratios even though both show acceptable model performance in the conventional model performance evaluation. This calls for development of model performance evaluation criteria specific to various regulatory purposes.

The anthropogenic increment of a species is the difference in concentration between a base-case simulation with all emissions included and a background simulation without the anthropogenic emissions. The Path-Integral Method (PIM) is a new technique that can determine the contributions of individual anthropogenic sources to this increment. The PIM was applied to a simulation of O3 formation in July 2030 in the U.S., using the Comprehensive Air Quality Model with Extensions and assuming advanced controls on light-duty vehicles (LDVs) and other sources. The PIM determines the source contributions by integrating first-order sensitivity coefficients over a range of emissions, a path, from the background case to the base case. There are many potential paths, with each representing a specific emission-control strategy leading to zero anthropogenic emissions, i.e., controlling all sources together versus controlling some source(s) preferentially are different paths. Three paths were considered, and the O3, formaldehyde, and NO2 anthropogenic increments were apportioned to five source categories. At rural and urban sites in the eastern U.S. and for all three paths, point sources typically have the largest contribution to the O3 and NO2 anthropogenic increments, and either LDVs or area sources, the smallest. Results for formaldehyde are more complex.

The decoupled direct method for sensitivity analysis was extended to the rate terms for the loss of reactants and formation of products to provide a detailed understanding of the predictions of chemical mechanisms used in atmospheric models. A box-model version and the full three-dimensional (3-D) version of the Comprehensive Air Quality Model with Extensions were used to calculate sensitivities to rate terms in the Carbon Bond 2005 chemical mechanism. The processes studied were formation of products from oxidation of the more reactive organic compounds, removal of NO x by organic nitrate formation, re-formation of NO x from organic nitrates, and loss of OH and NO 2 and formation of HNO 3 in the reaction OH + NO 2 → HNO 3 . Simulations of the box model for four scenarios representing urban and rural atmospheres indicated that the largest sensitivities of ozone, formaldehyde and HO x were to rate terms for certain products of the oxidation of isoprene and to the reactants in OH + NO 2 → HNO 3 . The 3-D model was then applied to calculate sensitivities to these rate terms for an eastern U.S. ozone episode in July, 2008. The 3-D simulation results were better correlated with the more NO x -limited rural scenario of the box model and showed that the isoprene oxidation products with the greatest impact on O 3 formation are methacrolein, methyl vinyl ketone, HO 2 radical, and species converting NO to NO 2 and organic nitrates. The 3-D results also showed that loss of NO 2 was more important than loss of OH for O 3 formation in most areas of the eastern U.S. This work emphasizes the need for continued experimental work to understand the oxidation of isoprene because the isoprene chemistry influenced modeled ozone predictions for both urban as well as rural areas.

A hybrid volatility basis set (VBS) approach to modeling atmospheric organic aerosol (OA) is developed that combines the simplicity of the 1-dimensional (1-D) VBS with the ability to describe evolution of OA in the 2-dimensional space of oxidation state and volatility. This 1.5-D scheme uses four basis sets to describe varying degrees of oxidation in ambient OA: two basis sets for chemically aged oxygenated OA (anthropogenic and biogenic) and two for freshly emitted OA (from anthropogenic sources and biomass burning). Each basis set has five volatility bins including a zero-volatility bin for essentially non-volatile compounds. The scheme adjusts oxidation state as well as volatility in response to chemical aging by simplifying the 2-dimensional VBS model. The 1.5-D VBS module is implemented in two widely used photochemical grid models (CAMx and CMAQ) and evaluated for summer and winter 2005 episodes over the eastern U.S. CAMx performs reasonably well in predicting observed organic carbon (OC) concentrations while CMAQ under-estimates OC, with differences between models being attributed to science algorithms other than the VBS. Oxygenated OA accounts for less than half of the modeled OA mass in winter but about 80% of total OA in summer due to more rapid chemical aging in summer.

Air quality model results are used in a relative sense as part of the process to demonstrate attainment of the U.S. ozone standard. Ozone model predictions for a future year are divided by corresponding model results for a base year to obtain a Relative Reduction Factor (RRF), and the base-year measured ozone design value (DV) is multiplied by the RRF to estimate the future-year design value (DVF). We developed alternative RRFs and DVFs that focus on the increment of local ozone production above regional background (RB). An advantage of the alternative DVFs is that measurements can be used to determine RB ozone, thereby increasing the use of measurements in the DVF estimates. We simulated ozone formation in the Houston area for May–September 2012 and 2028 using the Comprehensive Air Quality Model with Extensions and compared the standard and alternative RRFs and DVFs. If model results are used for all the RB ozone concentrations in our new equation to calculate DVFs, the alternative and standard DVFs are very similar for Houston-Galveston-Brazoria (HGB). If measurements are used for the RB ozone concentrations we combine with the base-year DVs, the alternative DVFs are noticeably larger than the standard DVFs for about half the sites, with the increase being 7 ppb at the site (Deer Park) with the largest standard and alternative DVFs. The differences arise primarily from including different days in the averaging process for the RRFs versus the base-year DVs. We evaluated model performance for the days included in the RRFs and found that the model over-predicted RB ozone (normalized mean bias (NMB) = 26%) and under-predicted the anthropogenic ozone increment (NMB = -22%) from HGB emissions and therefore can be expected to under-estimate ozone response to HGB emission controls. Keywords: Ozone, Houston, Regional background, Relative reduction factor, Design value, CAMx

This study develops probabilistic estimates of ozone (O3) sensitivities to precursor emissions by incorporating uncertainties in photochemical modeling and evaluating model performance based on ground-level observations of O3 and oxides of nitrogen (NOx). Uncertainties in model formulations and input parameters are jointly considered to identify factors that strongly influence O3 concentrations and sensitivities in the Dallas-Fort Worth region in Texas. Weightings based on a Bayesian inference technique and screenings based on model performance and statistical tests of significance are used to generate probabilistic representation of O3 response to emissions and model input parameters. Adjusted (observation-constrained) results favor simulations using the sixth version of the carbon bond chemical mechanism (CB6) and scaled-up emissions of NOx, dampening the overall sensitivity of O3 to NOx and increasing the sensitivity of O3 to volatile organic compounds in the study region. This approach of using observations to adjust and constrain model simulations can provide probabilistic representations of pollutant responsiveness to emission controls that complement the results obtained from deterministic air-quality modeling.

The weekend ozone effect refers to changes in ground-level ozone concentrations on weekends resulting from anthropogenic emission changes from weekdays and weekends. This study applied a three-dimensional photochemical grid model for a three-month summer period to examine the weekend ozone effect in the Midwestern US (the north-central and north-eastern part of US) at both urban and regional scales. The model generally reproduced the observed daily maximum 1-h and 8-h ozone and also correctly predicted weekend changes in the VOC-to-NOx ratio. So-called dynamic evaluation of the modeled weekend ozone changes throughout the summer revealed that meteorology had a bigger impact on the summer 2005 weekend ozone effect than anthropogenic emission changes partly because meteorology strongly influences biogenic emissions. To avoid the confounding effect of meteorological changes, weekend ozone differences were determined by using a second simulation modeled with weekday emissions for all days of week. Ozone differences between the base case and the second simulation isolated the effect of weekday/weekend emission changes. To further distinguish local effects of weekend emission changes from transported regional ozone differences, a third simulation applied weekend emission changes only within two urban areas with all weekday emissions for the remaining areas. The ozone differences between the base case and the third simulations revealed that the effect of regional weekend emission differences is projected to be mostly lowered ozone on weekends. On the other hand, the difference between the second and third simulations revealed that weekend emission changes in two urban areas increased ozone locally in the urban centers and immediately downwind areas but lowered ozone further downwind. The sign-change in the weekend ozone effect from urban centers to downwind areas is explained by a matching change in sign of ozone sensitivity to NOx emissions which was confirmed by computing ozone sensitivities to domain-wide NOx and VOC emissions. The sensitivity analysis also showed that weekday/weekend ozone differences in the Midwestern US are due primarily to weekend reductions in NOx emissions.

Air quality models are increasingly used to develop estimates of dry and wet deposition of sulfate and nitrate in watersheds (because of lack of measurements) in an effort to determine the acidifying deposition load into the aquatic systems. These models need to be rigorously evaluated to ensure that one can rely on the modeled quantities instead of the measured quantities. In the United State (U.S.), these models have been proposed for use in establishing national standards based on modeled quantities. The U.S. Environmental Protection Agency (EPA) is considering aquatic acidification as the main ecological endpoint of concern in determining the secondary national ambient air quality standards for nitrogen oxides and sulfur oxides. Acidification is tied to depositions of sulfur and nitrogen, which are linked to ambient concentrations of the elements. As EPA proposes to use a chemical transport model in linking deposition to ambient concentration, it is important to investigate how the currently used chemical transport models perform in predicting depositions and ambient concentrations of relevant chemical species and quantify the variability in their estimates. In this study, several annual simulations by multiple chemical transport models for the entire continental U.S. domain are evaluated against available measurement data for depositions and ambient concentrations of sulfur oxides and reactive nitrogen species. The model performance results vary by evaluation time-scale and geographical region. Evaluation of annualized quantities (annual average ambient concentrations and annual total depositions) suppresses the large variances shown in the evaluation using the observation’s native shorter-term time-scales (e.g., weekly). In addition, there is a large degree of bias and error (especially for deposition fluxes) in the modeling results that brings to question the suitability of using air quality models to provide estimates of deposition loads. Variability in the ratio of deposition to ambient concentration, so-called the Transference Ratio that EPA has proposed to use in linking deposition to ambient concentration, is also examined. Our study shows that the Transference Ratios as well as total reduced nitrogen deposition, another modeled parameter EPA proposed to use in the process of determining the new secondary standard, vary considerably by geographical region and by model simulation.

Federal Tier 3 motor vehicle emission and fuel sulfur standards have been promulgated in the United States to help attain air quality standards for ozone and PM2.5 (particulate matter with an aerodynamic diameter2.5 μm). The authors modeled a standard similar to Tier 3 (a hypothetical nationwide implementation of the California Low Emission Vehicle [LEV] III standards) and prior Tier 2 standards for on-road gasoline-fueled light-duty vehicles (gLDVs) to assess incremental air quality benefits in the United States (U.S.) and the relative contributions of gLDVs and other major source categories to ozone and PM2.5 in 2030. Strengthening Tier 2 to a Tier 3-like (LEV III) standard reduces the summertime monthly mean of daily maximum 8-hr average (MDA8) ozone in the eastern U.S. by up to 1.5 ppb (or 2%) and the maximum MDA8 ozone by up to 3.4 ppb (or 3%). Reducing gasoline sulfur content from 30 to 10 ppm is responsible for up to 0.3 ppb of the improvement in the monthly mean ozone and up to 0.8 ppb of the improvement in maximum ozone. Across four major urban areas-Atlanta, Detroit, Philadelphia, and St. Louis-gLDV contributions range from 5% to 9% and 3% to 6% of the summertime mean MDA8 ozone under Tier 2 and Tier 3, respectively, and from 7% to 11% and 3% to 7% of the maximum MDA8 ozone under Tier 2 and Tier 3, respectively. Monthly mean 24-hr PM2.5 decreases by up to 0.5 μg/m(3) (or 3%) in the eastern U.S. from Tier 2 to Tier 3, with about 0.1 μg/m(3) of the reduction due to the lower gasoline sulfur content. At the four urban areas under the Tier 3 program, gLDV emissions contribute 3.4-5.0% and 1.7-2.4% of the winter and summer mean 24-hr PM2.5, respectively, and 3.8-4.6% and 1.5-2.0% of the mean 24-hr PM2.5 on days with elevated PM2.5 in winter and summer, respectively.Following U.S. Tier 3 emissions and fuel sulfur standards for gasoline-fueled passenger cars and light trucks, these vehicles are expected to contribute less than 6% of the summertime mean daily maximum 8-hr ozone and less than 7% and 4% of the winter and summer mean 24-hr PM2.5 in the eastern U.S. in 2030. On days with elevated ozone or PM2.5 at four major urban areas, these vehicles contribute less than 7% of ozone and less than 5% of PM2.5, with sources outside North America and U.S. area source emissions constituting some of the main contributors to ozone and PM2.5, respectively.

In this study, the lubrication characteristics of sliding members were compared with the changes in the hardness of friction surfaces and the application of nano-oil. The materials of the specimens were gray cast iron (AISI 35 and AISI 60) and nickel chromium molybdenum steel (AISI 4320). The friction coefficients and the temperature variations of the frictional surfaces were measured with a disk-on-disk tribotester under a fixed rotation speed. The friction surfaces were observed with a scanning electron microscope (SEM). The friction coefficients of the plate surface increased as the hardness difference increased. The friction coefficient after the lubrication with nano-oil was less than that after lubrication with mineral oil. This is because a spherical nanoparticle plays the role of a tiny ball bearing between the frictional surfaces that improve the lubrication characteristics.

Air quality models rely upon simplified photochemical mechanisms to efficiently represent the thousands of chemical species that interact to form air pollution. Uncertainties in the chemical reaction rate constants and photolysis frequencies that comprise those mechanisms can generate uncertainty in the estimation of pollutant concentrations and their responsiveness to emission controls. A high-order sensitivity analysis technique is applied to quantify the extent to which reaction rate uncertainties influence estimates of ozone concentrations and their sensitivities to precursor emissions during an air pollution episode in Houston, Texas. Several reactions were found to have much larger proportional effects on ozone’s sensitivities to emissions than on its concentrations. In particular, uncertainties in photolysis frequencies and in the rate of reaction between NO2 and OH to form nitric acid can significantly influence the magnitude and sign of peak ozone sensitivity to nitrogen oxide (NOx) emissions. Ozone sensitivity to VOCs exhibits a much more muted response to uncertainties in the reaction rate constants and photolysis frequencies considered here. The results indicate the importance of accurate reaction rate constants to predicting the ozone impacts resulting from NOx emission controls.

Natural emissions adopted in current regional air quality modeling are updated to better describe natural background ozone and PM concentrations for North America. The revised natural emissions include organosulfur from the ocean, NO from lightning, sea salt, biogenic secondary organic aerosol (SOA) precursors, and pre-industrial levels of background methane. The model algorithm for SOA formation was also revised. Natural background ozone concentrations increase by up to 4 ppb in annual average over the southeastern US and Gulf of Mexico due to added NO from lightning while the revised biogenic emissions produced less ozone in the central and western US. Natural PM2.5 concentrations generally increased with the revised natural emissions. Future year (2018) simulations were conducted for several anthropogenic emission reduction scenarios to assess the impact of the revised natural emissions on anthropogenic emission control strategies. Overall, the revised natural emissions did not significantly alter the ozone responses to the emissions reductions in 2018. With revised natural emissions, ozone concentrations were slightly less sensitive to reducing NOx in the southeastern US than with the current natural emissions due to higher NO from lightning. The revised natural emissions have little impact on modeled PM2.5 responses to anthropogenic emission reductions. However, there are substantial uncertainties in current representations of natural sources in air quality models and we recommend that further study is needed to refine these representations.

In this study, we used numerical models to investigate weekday to weekend ozone differences in the Los Angeles (LA) basin in 1997 and 2010. We developed relatively complete descriptions of weekday to weekend emission changes for nitrogen oxides (NOx) with 80% of the weekday NOx emissions receiving a weekend adjustment in 1997 and 67% in 2010. Weekend NOx decreases of 34% on Saturday and 45% on Sunday relative to weekdays for 1997 are predicted to become slightly greater by 2010 and are dominated by NOx decreases for on-road vehicles (especially heavy-duty diesel vehicles) and off-road construction equipment. Weekend anthropogenic reactive organic gas (ROG) decreases for 1997 (12% on Saturday and 16% on Sunday) are smaller than for NOx and become even smaller in 2010. However, there is less certainty in the weekend ROG emission changes because only 47% of the weekday ROG emissions received a weekend adjustment in 1997 and only 21% in 2010. The ozone modeling used multiple representations of the meteorology and chemistry in order to identify results that are consistent across these inputs. Weekend ozone increased in central portions of the basin in response to weekend NOx and ROG decreases for both 1997 and 2010, with both the SAPRC99 and CB4 chemical mechanisms, and with all meteorological data sets. Weekend ozone decreased in other portions of the basin in all models. Comparing 2010 to 1997, weekend ozone increases are smaller and confined to smaller portions of the LA basin near the Pacific coast, whereas weekend ozone decreases are larger and more widespread in 2010. For 2010, all models show lower 8-h ozone on Sunday than weekdays in the Riverside/San Bernardino area. First-order sensitivity analysis (via the decoupled direct method) shows that the weekday/weekend ozone changes are mainly due to the NOx emission changes. Also, the weekday/weekend ozone changes for 2010 are sensitive to the choice of initial and boundary concentrations.