Prasad S. Kasibhatla

Growth of Continental-Scale Metro-Agro-Plexes, Regional Ozone Pollution, and World Food Production

Three regions of the northern mid-latitudes, the continental-scale metro-agro-plexes, presently dominate global industrial and agricultural productivity. Although these regions cover only 23 percent of the Earths continents, they account for most of the worlds commercial energy consumption, fertilizer use, food-crop production, and food exports. They also account for more than half of the worlds atmospheric nitrogen oxide (NOx,) emissions and, as a result, are prone to ground-level ozone (O3) pollution during the summer months. On the basis of a global simulation of atmospheric reactive nitrogen compounds, it is estimated that about 10 to 35 percent of the worlds grain production may occur in parts of these regions where ozone pollution may reduce crop yields. Exposure to yield-reducing ozone pollution may triple by 2025 if rising anthropogenic NOx emissions are not abated.

Emission inventory development and processing for the Seasonal Model for Regional Air Quality (SMRAQ) project

This paper describes the experiences and insights gained from inventory preparation and emissions processing for the Seasonal Model for Regional Air Quality (SMRAQ) project. The emission inventory was derived from the 1990 and 1995 Ozone Transport Assessment Group (OTAG) inventories. Here we outline the emissions processing strategy used for the May-to-September simulation, summarize the inventory characteristics and corrections made on the OTAG inventories, and describe the quality assurance steps taken as part of the processing. We then provide spatial maps and daily total time series charts of the hourly, gridded emissions of nitrogen oxides (NOx), reactive organic gases (ROG), and carbon monoxide (CO). Large peaks from electric utility point sources and urban mobile sources characterize the NOx emissions, and the NOx emissions in nonpeak regions are primarily mobile-source emissions. ROG emissions are dominated by biogenic isoprene production in the southern United States, and they have a strong seasonal variability. CO emissions are characterized by less variability, with area and mobile sources dominating the inventory. We compare ratios of season-average nonmethane organic gases to NOx between the emission inventory and the Photochemical Assessment Monitoring Stations (PAMS) data, and these comparisons show poor correlation between the inventory and ambient ratios.

Evaluation and intercomparison of global atmospheric transport models using 222Rn and other short‐lived tracers

Simulations of 222Rn and other short-lived tracers are used to evaluate and intercompare the representations of convective and synoptic processes in 20 global atmospheric transport models. Results show that most established three-dimensional models simulate vertical mixing in the troposphere to within the constraints offered by the observed mean 222Rn concentrations and that subgrid parameterization of convection is essential for this purpose. However, none of the models captures the observed variability of 222Rn concentrations in the upper troposphere, and none reproduces the high 222Rn concentrations measured at 200 hPa over Hawaii. The established three-dimensional models reproduce the frequency and magnitude of high-222Rn episodes observed at Crozet Island in the Indian Ocean, demonstrating that they can resolve the synoptic-scale transport of continental plumes with no significant numerical diffusion. Large differences between models are found in the rates of meridional transport in the upper troposphere (interhemispheric exchange, exchange between tropics and high latitudes). The four two-dimensional models which participated in the intercomparison tend to underestimate the rate of vertical transport from the lower to the upper troposphere but show concentrations of 222Rn in the lower troposphere that are comparable to the zonal mean values in the three-dimensional models.

Effects of ship emissions on sulphur cycling and radiative climate forcing over the ocean

The atmosphere overlying the ocean is very sensitive—physically, chemically and climatically—to air pollution. Given that clouds over the ocean are of great climatic significance, and that sulphate aerosols seem to be an important control on marine cloud formation, anthropogenic inputs of sulphate to the marine atmosphere could exert an important influence on climate. Recently, sulphur emissions from fossil fuel burning by international shipping have been geographically characterized, indicating that ship sulphur emissions nearly equal the natural sulphur flux from ocean to atmosphere in many areas. Here we use a global chemical transport model to show that these ship emissions can be a dominant contributor to atmospheric sulphur dioxide concentrations over much of the worlds oceans and in several coastal regions. The ship emissions also contribute significantly to atmospheric non-seasalt sulphate concentrations over Northern Hemisphere ocean regions and parts of the Southern Pacific Ocean, and indirect radiative forcing due to ship-emitted particulate matter (sulphate plus organic material) is estimated to contribute a substantial fraction to the anthropogenic perturbation of the Earths radiation budget. The quantification of emissions from international shipping forces a re-evaluation of our present understanding of sulphur cycling and radiative forcing over the ocean.

Climate regulation of fire emissions and deforestation in equatorial Asia

Drainage of peatlands and deforestation have led to large-scale fires in equatorial Asia, affecting regional air quality and global concentrations of greenhouse gases. Here we used several sources of satellite data with biogeochemical and atmospheric modeling to better understand and constrain fire emissions from Indonesia, Malaysia, and Papua New Guinea during 2000–2006. We found that average fire emissions from this region [128 ± 51 (1σ) Tg carbon (C) year−1, T = 1012] were comparable to fossil fuel emissions. In Borneo, carbon emissions from fires were highly variable, fluxes during the moderate 2006 El Niño more than 30 times greater than those during the 2000 La Niña (and with a 2000–2006 mean of 74 ± 33 Tg C yr−1). Higher rates of forest loss and larger areas of peatland becoming vulnerable to fire in drought years caused a strong nonlinear relation between drought and fire emissions in southern Borneo. Fire emissions from Sumatra showed a positive linear trend, increasing at a rate of 8 Tg C year−2 (approximately doubling during 2000–2006). These results highlight the importance of including deforestation in future climate agreements. They also imply that land manager responses to expected shifts in tropical precipitation may critically determine the strength of climate–carbon cycle feedbacks during the 21st century.

Global distribution of carbon monoxide

This study explores the evolution and distribution of carbon monoxide (CO) using the National Oceanic and Atmospheric Administration (NOAA) Geophysical Fluid Dynamics Laboratory three-dimensional global chemical transport model (GFDL GCTM). The work aims to gain an improved understanding of the global carbon monoxide budget, specifically focusing on the contribution of each of the four source terms to the seasonal variability of CO. The sum of all CO sources in the model is 2.5 Pg CO/yr (1 Pg = 103 Tg), including fossil fuel use (300 Tg CO/yr), biomass burning (748 Tg CO/yr), oxidation of biogenic hydrocarbons (683 Tg CO/yr), and methane oxidation (760 Tg CO/yr). The main sink for CO is destruction by the hydroxyl radical, and we assume a hydroxyl distribution based on three-dimensional monthly varying fields given by Spivakovsky et al. [1990], but we increase this field by 15% uniformly to agree with a methyl chloroform lifetime of 4.8 years [Prinn et al, 1995]. Our simulation produces a carbon monoxide field that agrees well with available measurements from the NOAA/Climate Monitoring and Diagnostics Laboratory global cooperative flask sampling network and from the Jungfraujoch observing station of the Swiss Federal Laboratories for Materials Testing and Research (EMPA) (93% of seasonal-average data points agree within ±25%) and flight data from measurement campaigns of the NASA Global Tropospheric Experiment (79% of regional-average data points agree within ±25%). For all 34 ground-based measurement sites we have calculated the percentage contribution of each CO source term to the total model-simulated distribution and examined how these contributions vary seasonally due to transport, changes in OH concentration, and seasonality of emission sources. CO from all four sources contributes to the total magnitude of CO in all regions. Seasonality, however, is usually governed by the transport and destruction by OH of CO emitted by fossil fuel and/or biomass burning. The sensitivity to the hydroxyl field varies spatially, with a 30% increase in OH yielding decreases in CO ranging from 4–23%, with lower sensitivities near emission regions where advection acts as a strong local sink. The lifetime of CO varies from 10 days over summer continental regions to well over a year at the winter poles, where we define lifetime as the turnover time in the troposphere due to reaction with OH.

Simulated global tropospheric PAN: Its transport and impact on NO x

Using the 11-level Geophysical Fluid Dynamics Laboratory (GFDL) global chemical transport model (GCTM) with all known sources of tropospheric NOx, we simulate the global tropospheric distribution of peroxyacetyl nitrate (PAN) and quantify its impact on tropospheric NOx. The models global distribution of PAN is in reasonable agreement with most available observations. In the atmospheric boundary layer, PAN is concentrated over the continental sites of NOx emissions, primarily the midlatitudes in the northern hemisphere and the subtropics in the southern hemisphere. PAN is distributed relatively zonally throughout the free troposphere of the northern hemisphere, with the maximum levels found in the coldest regions, while in the southern hemisphere the maximum PAN levels are found in an equator to 30°S belt stretching from South America to Australia. Overall, the simulated three-dimensional fields of seasonal PAN are a result of the interaction of the type of transport meteorology (convective or synoptic scale storms) occurring in the PAN formation regions and PANs temperature-dependent lifetime. We find the impact of PAN chemistry on NOx to be rather subtle. The magnitude and the seasonal cycle of the global tropospheric integral of NOx, which has its maximum in January and the formation of HNO3 as its dominant loss path, are barely affected by the inclusion of PAN chemistry, however PAN, as a result of its temperature sensitivity and transport, regionally provides an efficient mechanism for redistributing NOx far from its source areas. With the inclusion of PAN chemistry, monthly mean NOx concentrations increase by up to a factor of 5 in the remote lower troposphere and show a spring maximum over areas of the North Atlantic and North Pacific Oceans. In contrast, PAN has only a minor impact in the upper half of the troposphere (±10%). Examining local time series of NOx and PAN, the monthly mean mixing ratios in remote regions are shown to be composed of numerous short-term (1–2 days) large magnitude events. These episodes are large enough to potentially result in ozone production even when the monthly mean NOx values are in the ozone destruction range. While both the direct transport of NOx and its indirect transport as PAN contribute to the elevated NOx episodes over the remote extratropical oceans, events over the remote subtropical oceans are dominated by midtropospheric PAN that sinks anticyclonically equatorward and decomposes to NOx in the warmer air.

Daily and 3‐hourly variability in global fire emissions and consequences for atmospheric model predictions of carbon monoxide

Attribution of the causes of atmospheric trace gas and aerosol variability often requires the use of high resolution time series of anthropogenic and natural emissions inventories. Here we developed an approach for representing synoptic- and diurnal-scale temporal variability in fire emissions for the Global Fire Emissions Database version 3 (GFED3). We disaggregated monthly GFED3 emissions during 2003–2009 to a daily time step using Moderate Resolution Imaging Spectroradiometer (MODIS)-derived measurements of active fires from Terra and Aqua satellites. In parallel, mean diurnal cycles were constructed from Geostationary Operational Environmental Satellite (GOES) Wildfire Automated Biomass Burning Algorithm (WF_ABBA) active fire observations. Daily variability in fires varied considerably across different biomes, with short but intense periods of daily emissions in boreal ecosystems and lower intensity (but more continuous) periods of burning in savannas. These patterns were consistent with earlier field and modeling work characterizing fire behavior dynamics in different ecosystems. On diurnal timescales, our analysis of the GOES WF_ABBA active fires indicated that fires in savannas, grasslands, and croplands occurred earlier in the day as compared to fires in nearby forests. Comparison with Total Carbon Column Observing Network (TCCON) and Measurements of Pollution in the Troposphere (MOPITT) column CO observations provided evidence that including daily variability in emissions moderately improved atmospheric model simulations, particularly during the fire season and near regions with high levels of biomass burning. The high temporal resolution estimates of fire emissions developed here may ultimately reduce uncertainties related to fire contributions to atmospheric trace gases and aerosols. Important future directions include reconciling top-down and bottom up estimates of fire radiative power and integrating burned area and active fire time series from multiple satellite sensors to improve daily emissions estimates.

Forecasting Fire Season Severity in South America Using Sea Surface Temperature Anomalies

Sea surface temperature anomalies can predict annual fire season severity in South America up to 3 to 5 months in advance. Fires in South America cause forest degradation and contribute to carbon emissions associated with land use change. We investigated the relationship between year-to-year changes in fire activity in South America and sea surface temperatures. We found that the Oceanic Niño Index was correlated with interannual fire activity in the eastern Amazon, whereas the Atlantic Multidecadal Oscillation index was more closely linked with fires in the southern and southwestern Amazon. Combining these two climate indices, we developed an empirical model to forecast regional fire season severity with lead times of 3 to 5 months. Our approach may contribute to the development of an early warning system for anticipating the vulnerability of Amazon forests to fires, thus enabling more effective management with benefits for climate and air quality.

A three-dimensional global model investigation of seasonal variations in the atmospheric burden of anthropogenic sulfate aerosols

A global three-dimensional chemical transport model is used to investigate seasonal variations of anthropogenic sulfur in the troposphere. Particular emphasis is placed on detailed comparisons of the modeled surface sulfur dioxide (SO2) and sulfate (SO4) concentrations and sulfate wet deposition fluxes with measurements from the Eulerian Model Evaluation Field Study (EMEFS) and Cooperative Program for Monitoring and Evaluation of the Long Range Transmission of Air Pollutants in Europe (EMEP) field programs in North America and Europe, respectively. Initial comparisons of model results with measurements reveal a systematic tendency of the model to overestimate SO2 concentrations and underestimate SO4 concentrations while producing a reasonable fit to measured wet deposition fluxes. Through a series of sensitivity tests we find that the addition of a nonphotochemical pathway for converting SO2 to SO4 in the boundary layer with a pseudo first-order rate of constant of 1–2×10−6 s−1 provides the most reasonable method of bringing the model results into better agreement with the EMEFS and EMEP data sets. We propose that this additional pathway may be related to heterogeneous reactions between SO2 and atmospheric aerosols that typically are not included in models of the atmospheric sulfur cycle. Despite the vastly improved simulation of surface SO2 and SO4 when this hypothetical heterogeneous oxidation pathway is included, the model is unable to simultaneously simulate the large seasonal cycle in surface SO4 observed over eastern North America and the almost total absence of a seasonal cycle in surface SO4 over Europe. The seasonal cycles in model-predicted column SO4 burdens are similar, but not identical, to those for surface SO4 because of regional differences in transport, free tropospheric oxidation, and in-cloud removal. We find that the summer-to-winter ratio in column SO4 is larger over eastern North America than it is over Europe; however, both are larger than that for eastern Asia, where wintertime column SO4 is predicted to exceed summertime column SO4.