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Wildfires emit vast amounts of aerosols and trace gases into the atmosphere, exerting myriad effects on air quality, climate, and human health. Ensemble forecasting has been proposed to reduce the large uncertainties in the wildfire air pollution forecast. This study presents the development of a multi‐model ensemble (MME) wildfire air pollution forecast over North America. The ensemble members include regional models (GMU‐CMAQ, NACC‐CMAQ, and HYSPLIT), global models (GEFS‐Aerosols, GEOS5, and NAAPS), and global ensemble (ICAP‐MME). Performance of the ensemble forecast was evaluated with MAIAC and VIIRS‐SNPP retrieved aerosol optical depth (AOD) and AirNow surface PM2.5 measurements during the 2020 Western United States "Gigafire" events (August–September 2020). Compared to individual models, the ensemble mean significantly reduced the biases and produced more consistent and reliable forecasts during extreme fire events. For AOD forecasts, the ensemble mean was able to improve model performance, such as increasing the correlation to 0.62 from 0.33 to 0.57 by individual models compared to VIIRS AOD. The ensemble mean also yields the best overall RANK (a composite indicator of four statistical metrics) when compared to VIIRS and MAIAC AOD. For the surface PM2.5 forecast, the ensemble mean outperformed individual models with the strongest correlation (0.60 vs. 0.43–0.54 by individual models), lowest fractional bias (0.54 vs. 0.55–1.32), highest hit rate (87% vs. 40%–82%), and highest RANK (2.83 vs. 2.40–2.81). Finally, the ensemble shows the potential to provide a probability forecast of air quality exceedances. The exceedance probability forecast can be further applied to early warnings of extreme air pollution episodes during large wildfire events. Plain Language Summary: Wildfires are a major source of air pollution emitting large quantities of particles into the air that adversely affect human health. Predicting wildfire air pollution, however, is challenging. Ensemble forecasting has been proposed to improve the model predictability. We developed a new multi‐model ensemble forecast system of wildfire air pollution over North America, leveraging regional and global atmospheric models by federal agencies and academia. How well the ensemble forecast can predict wildfire pollution was evaluated with observations from satellites and ground monitors. We found that the ensemble mean can significantly reduce the forecast biases and produce more reliable forecasts during extreme wildfire fire events. The ensemble probability forecast of exceedance of the health‐based National Ambient Air Quality Standards for fine particles (PM2.5) can be further applied to early warnings of severe air pollution episodes during large wildfire events. These findings highlight the potential of the ensemble approach to improve the predictability of air pollution during large wildfires. Key Points: Ensemble mean of models provides reliable aerosol optical depth and PM2.5 forecasts with stronger correlation, lower bias, and the highest overall RANKsThe ensemble approach provides a well suited exceedance probability forecast during the 2020 Gigafire eventsThe multi‐model ensemble approach can reduce uncertainties in air quality forecasts and improve model predictability during wildfire events [ABSTRACT FROM AUTHOR]

Forest canopies are primary emission sources of biogenic volatile organic compounds (BVOCs) and have the potential to significantly influence the formation and distribution of secondary organic aerosol (SOA) mass. Biogenically-derived SOA formed as a result of emissions from the widespread forests across the globe may affect air quality in populated areas, degrade atmospheric visibility, and affect climate through direct and indirect forcings. In an effort to better understand the formation of SOA mass from forest emissions, a 1-D column model of the multiphase physical and chemical processes occurring within and just above a vegetative canopy is being developed. An initial, gas-phase-only version of this model, the Atmospheric Chemistry and Canopy Exchange Simulation System (ACCESS), includes processes accounting for the emission of BVOCs from the canopy, turbulent vertical transport within and above the canopy and throughout the height of the planetary boundary layer (PBL), near-explicit representation of chemical transformations, mixing with the background atmosphere and bi-directional exchange between the atmosphere and canopy and the atmosphere and forest floor. The model formulation of ACCESS is described in detail and results are presented for an initial application of the modeling system to Walker Branch Watershed, an isoprene-emission-dominated forest canopy in the southeastern United States which has been the focal point for previous chemical and micrometeorological studies. Model results of isoprene profiles and fluxes are found to be consistent with previous measurements made at the simulated site and with other measurements made in and above mixed deciduous forests in the south-eastern United States. Sensitivity experiments are presented which explore how canopy concentrations and fluxes of gas-phase precursors of SOA are affected by background anthropogenic nitrogen oxides (NOx). Results from these experiments suggest that the level of ambient NOx influences the pathways by which SOA is formed by affecting the relative magnitudes and fluxes of isoprene oxidation products emitted from the canopy. Future versions of the ACCESS model are planned to be multiphase, including gas- and aerosol-phase chemical and physical processes, to more fully explore these preliminary results. [ABSTRACT FROM AUTHOR]

The processes of aerosol sulfate formation are vital components in the scientific understanding of perturbations of earth's radiative balance via aerosol direct and indirect effects. In this work, an analysis of the influence of changes in oxidant levels and sulfur dioxide oxidation pathways was performed to study the underlying pathways for sulfate formation. Sensitivities of this constituent were calculated from a series of photochemical model simulations with varying rates of NOx and VOC emissions to produce variations in oxidant abundances using a photochemical model (CMAQ) that covers the eastern US for part of the ICARTT 2004 campaign. Three different chemical mechanisms (CBIV, CB05, SAPRC99) were used to test model responses to changes in NOx and VOC concentrations. Comparison of modeled results and measurements demonstrates that the simulations with all three chemical mechanisms capture the levels of sulfate reasonably well. However, the three mechanisms are shown to have significantly different responses in sulfate formation when the emissions of NOx and/or VOC are altered, reflecting different photochemical regimes under which the formation of sulfate occurs. Also, an analysis of the oxidation pathways that contribute to sulfur dioxide conversion to sulfate reveals substantial differences in the importance of the various pathways among the three chemical mechanisms. These findings suggest that estimations of the influence that future changes in primary emissions or other changes which perturb SO2 oxidants have on sulfate abundances, on its direct and indirect radiative forcing effects, may be dependent on the chemical mechanism employed in the model analysis. [ABSTRACT FROM AUTHOR]

Forest canopies are primary emission sources of biogenic volatile organic compounds (BVOCs) and have the potential to significantly influence the formation and distribution of secondary organic aerosol (SOA) mass. Biogenically-derived SOA formed as a result of emissions from the widespread forests across the globe may affect air quality in populated areas, degrade atmospheric visibility, and affect climate through direct and indirect forcings. In an effort to better understand the formation of SOA mass from forest emissions, a 1-D column model of the physical and chemical processes occurring within and just above a vegetative canopy has been created. This model, the Atmospheric Chemistry and Canopy Exchange Simulation System (ACCESS), includes processes accounting for the emission of BVOCs from the canopy, turbulent vertical transport within and above the canopy and throughout the height of the planetary boundary layer (PBL), near-explicit representation of chemical transformations, mixing with the background atmosphere and bi-directional exchange between the atmosphere and canopy and the atmosphere and forest floor. The model formulation of ACCESS is described in detail and results are presented for an initial application of the modeling system to Walker Branch Watershed, an isoprene-emission-dominated forest canopy in the Southeastern United States which has been the focal point for previous chemical and micrometeorological studies. Model results of isoprene profiles and fluxes are found to be consistent with previous measurements made at the simulated site and with other measurements made in and above mixed deciduous forests in the Southeastern United States. Sensitivity experiments exploring how canopy concentrations and fluxes of gas-phase precursors of SOA are affected by background anthropogenic nitrogen oxides suggest potentially significant non-linearities in the chemical and physical system of the canopy which may have an impact on the relative magnitude of SOA 25 formed through aqueous- versus gas-phase pathways as a function of anthropogenic influence. [ABSTRACT FROM AUTHOR]

The processes of aerosol sulfate formation are vital components in the scientific understanding of perturbations of earth's radiative balance via aerosol direct and indirect effects. In this work, an analysis of the influence of changes in oxidant levels and sulfur dioxide oxidation pathways was performed to study the underlying pathways for sulfate formation. Sensitivities of this constituent were calculated from a series of photo-chemical model simulations with varying rates of NOx and VOC emissions to produce variations in oxidant abundances using a photochemical model (CMAQ) that covers the Eastern US for the ICARTT 2004 campaign. Three different chemical mechanisms (CBIV, CB05, and SAPRC99) were used to test model responses to changes in NOx and VOC levels. Comparison of modeled results and measurements demonstrates that the simulations with all three chemical mechanisms capture the levels of sulfate reasonably well. However, the three mechanisms are shown to have significantly different responses in sulfate formation when the emissions of NOx and/or VOC are altered, reflecting different photochemical regimes under which the formation of sulfate occurs. Also, an analysis of the oxidation pathways that contribute to sulfur dioxide conversion to sulfate reveals substantial differences in the importance of the various pathways among the three chemical mechanisms. These findings suggest that estimations of the influence that future changes in primary emissions or other changes which perturb SO2 oxidants have on sulfate abundances, and on its direct and indirect radiative forcing effects, may be dependent on the chemical mechanism employed in the model analysis. [ABSTRACT FROM AUTHOR]

The article presents a study which investigates the differences in ozone production from the CB05 and CBMIV carbon bond gas-phase chemical mechanisms. The ozone concentrations produced from the CB05 version of the National Air Quality Forecasting Capability (NAQFC) modeling system is highlighted. The NAQFC was developed by the U.S. National Oceanic & Atmospheric Administration (NOAA) to provide forecasts on the ground-level ozone.

The article presents a study on differences in ozone production from carbon bond gas-phase chemical mechanism versions CB05 and CBMIV. It mentions the creation of the mechanisms' box model as enforced in the National Air Quality Forecasting Capability (NAQFC) modeling system as well as the development of 12 sensitivity simulations. It also notes the emulation of their chemical regime range in a continental-scale atmospheric chemistry model.

Nerlovian supply functions are fitted to post-World War II coffee data for Sao Paulo, Brazil. Supply shifts are permitted through the use of dummy variables, and recent specifications of irreversible functions are tested. The modified Nerlovian functions perform best from both the economic and statistical point of view. [ABSTRACT FROM AUTHOR]

Comments on a study by Harry W. Ayer and G. Edward Schuh which estimated internal rates of return to cotton research in Sao Paulo, Brazil. Difference between experimental and farm-level yields; Rate of return using farm-level yield data; Discussion on the partial equilibrium nature of the study.

Comments on an article dealing with an approach in calculating the social rates of return of investments of cotton research in Sao Paolo, Brazil. Disadvantages of using the partial equilibrium model; Approach in calculating foreign demand.