Mark Z. Jacobson

Strong radiative heating due to the mixing state of black carbon in atmospheric aerosols

Aerosols affect the Earths temperature and climate by altering the radiative properties of the atmosphere. A large positive component of this radiative forcing from aerosols is due to black carbon—soot—that is released from the burning of fossil fuel and biomass, and, to a lesser extent, natural fires, but the exact forcing is affected by how black carbon is mixed with other aerosol constituents. From studies of aerosol radiative forcing, it is known that black carbon can exist in one of several possible mixing states; distinct from other aerosol particles (externally mixed) or incorporated within them (internally mixed), or a black-carbon core could be surrounded by a well mixed shell. But so far it has been assumed that aerosols exist predominantly as an external mixture. Here I simulate the evolution of the chemical composition of aerosols, finding that the mixing state and direct forcing of the black-carbon component approach those of an internal mixture, largely due to coagulation and growth of aerosol particles. This finding implies a higher positive forcing from black carbon than previously thought, suggesting that the warming effect from black carbon may nearly balance the net cooling effect of other anthropogenic aerosol constituents. The magnitude of the direct radiative forcing from black carbon itself exceeds that due to CH4, suggesting that black carbon may be the second most important component of global warming after CO2 in terms of direct forcing.

Review of solutions to global warming, air pollution, and energy security

This paper reviews and ranks major proposed energy-related solutions to global warming, air pollution mortality, and energy security while considering other impacts of the proposed solutions, such as on water supply, land use, wildlife, resource availability, thermal pollution, water chemical pollution, nuclear proliferation, and undernutrition. Nine electric power sources and two liquid fuel options are considered. The electricity sources include solar-photovoltaics (PV), concentrated solar power (CSP), wind, geothermal, hydroelectric, wave, tidal, nuclear, and coal with carbon capture and storage (CCS) technology. The liquid fuel options include corn-ethanol (E85) and cellulosic-E85. To place the electric and liquid fuel sources on an equal footing, we examine their comparative abilities to address the problems mentioned by powering new-technology vehicles, including battery-electric vehicles (BEVs), hydrogen fuel cell vehicles (HFCVs), and flex-fuel vehicles run on E85. Twelve combinations of energy source-vehicle type are considered. Upon ranking and weighting each combination with respect to each of 11 impact categories, four clear divisions of ranking, or tiers, emerge. Tier 1 (highest-ranked) includes wind-BEVs and wind-HFCVs. Tier 2 includes CSP-BEVs, geothermal-BEVs, PV-BEVs, tidal-BEVs, and wave-BEVs. Tier 3 includes hydro-BEVs, nuclear-BEVs, and CCS-BEVs. Tier 4 includes corn- and cellulosic-E85. Wind-BEVs ranked first in seven out of 11 categories, including the two most important, mortality and climate damage reduction. Although HFCVs are much less efficient than BEVs, wind-HFCVs are still very clean and were ranked second among all combinations. Tier 2 options provide significant benefits and are recommended. Tier 3 options are less desirable. However, hydroelectricity, which was ranked ahead of coal-CCS and nuclear with respect to climate and health, is an excellent load balancer, thus recommended. The Tier 4 combinations (cellulosic- and corn-E85) were ranked lowest overall and with respect to climate, air pollution, land use, wildlife damage, and chemical waste. Cellulosic-E85 ranked lower than corn-E85 overall, primarily due to its potentially larger land footprint based on new data and its higher upstream air pollution emissions than corn-E85. Whereas cellulosic-E85 may cause the greatest average human mortality, nuclear-BEVs cause the greatest upper-limit mortality risk due to the expansion of plutonium separation and uranium enrichment in nuclear energy facilities worldwide. Wind-BEVs and CSP-BEVs cause the least mortality. The footprint area of wind-BEVs is 2–6 orders of magnitude less than that of any other option. Because of their low footprint and pollution, wind-BEVs cause the least wildlife loss. The largest consumer of water is corn-E85. The smallest are wind-, tidal-, and wave-BEVs. The US could theoretically replace all 2007 onroad vehicles with BEVs powered by 73 000–144 000 5 MW wind turbines, less than the 300 000 airplanes the US produced during World War II, reducing US CO2 by 32.5–32.7% and nearly eliminating 15 000/yr vehicle-related air pollution deaths in 2020. In sum, use of wind, CSP, geothermal, tidal, PV, wave, and hydro to provide electricity for BEVs and HFCVs and, by extension, electricity for the residential, industrial, and commercial sectors, will result in the most benefit among the options considered. The combination of these technologies should be advanced as a solution to global warming, air pollution, and energy security. Coal-CCS and nuclear offer less benefit thus represent an opportunity cost loss, and the biofuel options provide no certain benefit and the greatest negative impacts.

Control of fossil-fuel particulate black carbon and organic matter, possibly the most effective method of slowing global warming

Under the 1997 Kyoto Protocol, no control of black carbon (BC) was considered. Here, it is found, through simulations in which 12 identifiable effects of aerosol particles on climate are treated, that any emission reduction of fossil-fuel (f.f.) particulate BC plus associated organic matter (OM) may slow global warming more than may any emission reduction of CO 2 or CH 4 for a specific period. When all f.f. BC + OM and anthropogenic CO 2 and CH 4 emissions are eliminated together, the period is 25-100 years. It is also estimated that historical net global warming can be attributed roughly to greenhouse gas plus f.f. BC + OM warming minus substantial cooling by other particles. Eliminating all f.f. BC + OM could eliminate 20-45% of net warming (8-18% of total warming before cooling is subtracted out) within 3-5 years if no other change occurred. Reducing CO 2 emissions by a third would have the same effect, but after 50-200 years. Finally, diesel cars emitting continuously under the most recent U.S. and E.U. particulate standards (0.08 g/mi; 0.05 g/km) may warm climate per distance driven over the next 100+ years more than equivalent gasoline cars. Thus, fuel and carbon tax laws that favor diesel appear to promote global warming. Toughening vehicle particulate emission standards by a factor of 8 (0.01 g/ mi; 0.006 g/km) does not change this conclusion, although it shortens the period over which diesel cars warm to 13-54 years. Although control of BC + OM can slow warming, control of greenhouse gases is necessary to stop warming. Reducing BC + OM will not only slow global warming but also improve human health.

A physically-based treatment of elemental carbon optics: Implications for global direct forcing of aerosols

To date, global models of direct radiative forcing have treated elemental carbon (EC) as completely externally mixed or well-mixed internally. No global study has treated EC as a core in an internal mixture. It is hypothesized that the well-mixed treatment is unphysical and reality lies between the externally-mixed and core treatments. It is also suggested, but not proven, that most EC particles are coated to some degree; hence, the core treatment may be more representative than the external-mixture treatment. Global simulations with the core treatment resulted in EC forcing 50% higher and 40% lower than forcings obtained with the externally-mixed and well-internally-mixed treatments, respectively. In the core case, ECs positive forcing more than offset negative forcing due to all other anthropogenic aerosol components combined. Further studies are needed to understand the mixing state of EC and determine the accuracy of the core treatment.

Global direct radiative forcing due to multicomponent anthropogenic and natural aerosols

Global simulations of the composition of and direct forcing due to aerosols containing natural and/or anthropogenic sulfate, nitrate, chloride, carbonate, ammonium, sodium, calcium, magnesium, potassium, black carbon, organic matter, silica, ferrous oxide, and aluminum oxide were carried out. Chloride and natural sulfate were found to be the most important natural aerosol constituents in the atmosphere in terms of solar plus thermal-infrared forcing. Sea spray was the most important natural aerosol type, indicating that it should be accounted for in weather and climate calculations. Ammonium was found to have a positive direct forcing, since it reduces water uptake in sulfate-containing solutions; thus, anthropogenic ammonium contributes to global warming. The magnitudes of ammonium and nitrate forcing were smaller than those of chloride or sulfate forcing. When organics were divided into three groups with different assumed UV absorption characteristics, total aerosol direct forcing at the tropopause increased by about +0.03 to +0.05 W m−2 (direct forcing by organics remained negative), suggesting that UV absorption by organics is a nontrivial component of the global energy balance. Gypsum [CaSO4-2H2O], sal ammoniac [NH4Cl], halite [NaCl], halite, and nitrum [KNO3] were estimated to be the most common sulfate-, ammonium-, sodium-, chloride-, and nitrate-containing solid-phase aerosol constituents, respectively, in the global atmosphere. Solid formation in aerosols was found to increase total-aerosol direct forcing by +0.03 to +0.05 W m−2. Spatial and vertical forcing estimates, sensitivities of forcing to relative humidity and concentration, and estimates of global aerosol liquid water content are given. Modeled aerosol optical properties are compared with satellite and field measurements.

Isolating nitrated and aromatic aerosols and nitrated aromatic gases as sources of ultraviolet light absorption

Measurements in 1973 and 1987 showed that downward ultraviolet (UV) irradiances within the boundary layer in Los Angeles were up to 50% less than those above the boundary layer. Downward total solar irradiances were reduced by less than 14% in both studies. It is estimated that standard gas and particulate absorbers and scatterers accounted for only about 52–62% of the observed UV reductions at Claremont and Riverside. It is hypothesized that absorption by nitrated and aromatic aerosol components and nitrated aromatic gases caused at least 25–30% of the reductions (with aerosols accounting for about 4/5 of this percent). The remaining reductions are still unaccounted for. Absorbing aerosol components include nitrated aromatics, benzaldehydes, benzoic acids, aromatic polycarboxylic acids, phenols, polycyclic aromatic hydrocarbons, and nitrated inorganics. Many of these species have been observed to date in atmospheric particles, and absorption coefficient data indicate many are strong absorbers at long UV wavelengths. Since aerosols containing nitrated or aromatic aerosols have been observed widely in many areas aside from Los Angeles the finding may account for a portion of UV extinction in those regions as well. In Los Angeles, the finding may be important for predicting smog evolution, since UV reductions associated with high aerosol loadings were estimated to cause a 5–8% decrease in ozone mixing ratios in August 1987. Further laboratory and field studies are needed to quantify better the extent of UV absorption due to nitrated and aromatic aerosols and nitrated aromatic gases.

Development and application of a new air pollution modeling system—II. Aerosol module structure and design

Abstract The methods used for simulating aerosol physical and chemical processes in a new air pollution modeling system are discussed and analyzed. Such processes include emissions, nucleation, coagulation, reversible chemistry, condensation, dissolution, evaporation, irreversible chemistry, sedimentation, dry deposition, and radiative scattering and absorption by particles. A new particle size bin structure that nearly eliminates numerical diffusion during growth but still treats nucleation, emissions, coagulation, and transport realistically is discussed. In addition, coagulation is shown to reduce the number and volume concentration of particles less than 0.2 μm in diameter both in the presence and absence of modest rates of particle growth. However, when significant growth occurs, the effect of coagulation is reduced. Further, while sulfate production due to SO2 dissolution and oxidation in cloud drops is confirmed to be important, it is shown here that such production in aerosols is small over time periods simulated in urban air pollution models. Finally, light scattering and absorption coefficient predictions, obtained by applying a Mie code for stratified spheres, are discussed and shown to match data for a given scenario. Remaining processes in the aerosol module are described.

SMVGEAR : a sparse-matrix, vectorized Gear code for atmospheric models

Abstract We present a Gear-type code that efficiently solves ordinary differential equations in large grid-domains. To obtain the final code, we modified an original program of C.W. Gear, built and added a sparse-matrix package, and vectorized all loops about the grid-cell dimension. Furthermore, to obtain at least 90% vectorization potential while preventing equations in some regions of the grid from slowing the solution over the entire grid-domain, we divided the domain into blocks of grid-cells and vectorized around these blocks. The sparse-matrix solution reduced the average number of LU-decomposition calculations, compared to a full-matrix solution, by factors of between 20 (for a matrix of order 40) and 120 (for a matrix of order 90). It also reduced both back-substitution calculations and total array space by factors of between 5 and 12 for the above matrix sizes. Vectorization on a CRAY-90 computer increased the speed by another factor of about 120 over the code running in scalar form. We tested the speed and accuracy of the program for several chemical applications on a single processor of the CRAY-90 computer. The code averaged between 1 and 2 min of computer time per day of simulation to solve a smog-chemistry set of 92 specied and 222 reactions over a 10,000-cell grid, with continuously changing photorates. It also took 3–4 min per day to solve a stratospheric-chemistry set of 39 species and 108 reactions over a 100,000-cell grid. In addition, we tested the speed of the code while it solved aqueous chemistry in 43 aerosol size bins, along with other physical processes and transport, over a large grid. Finally, we compared the speed and other statistics from SMVGEAR to those of an existing sparse matrix Gear code, LSODES, and to a new method that we call the Multistep Implicit-Explicit (MIE) method.

Short‐term effects of controlling fossil‐fuel soot, biofuel soot and gases, and methane on climate, Arctic ice, and air pollution health

[1] This study examines the short-term (∼15 year) effects of controlling fossil-fuel soot (FS) (black carbon (BC), primary organic matter (POM), and S(IV) (H 2 SO 4 (aq), HSO ― 4 , and SO 2― 4 ), solid-biofuel soot and gases (BSG) (BC, POM, S(IV), K + , Na + , Ca 2+ , Mg 2+ , NH + 4 , NO ― 3 , Cl - and several dozen gases, including CO 2 and CH 4 ), and methane on global and Arctic temperatures, cloudiness, precipitation, and atmospheric composition. Climate response simulations were run with GATOR-GCMOM, accounting for both microphysical (indirect) and radiative effects of aerosols on clouds and precipitation. The model treated discrete size-resolved aging and internal mixing of aerosol soot, discrete size-resolved evolution of clouds/precipitation from externally and internally mixed aerosol particles, and soot absorption in aerosols, clouds/precipitation, and snow/sea ice. Eliminating FS, FS+BSG (FSBSG), and CH 4 in isolation were found to reduce global surface air temperatures by a statistically significant 0.3-0.5 K, 0.4-0.7 K, and 0.2-0.4 K, respectively, averaged over 15 years. As net global warming (0.7-0.8 K) is due mostly to gross pollutant warming from fossil-fuel greenhouse gases (2-2.4 K), and FSBSG (0.4-0.7 K) offset by cooling due to non-FSBSG aerosol particles (-1.7 to -2.3 K), removing FS and FSBSG may reduce 13-16% and 17-23%, respectively, of gross warming to date. Reducing FS, FSBSG, and CH 4 in isolation may reduce warming above the Arctic Circle by up to ∼1.2 K, ∼1.7 K, and ∼0.9 K, respectively. Both FS and BSG contribute to warming, but FS is a stronger contributor per unit mass emission. However, BSG may cause 8 times more mortality than FS. The global e-folding lifetime of emitted BC (from all fossil sources) against internal mixing by coagulation was ∼3 h, similar to data, and that of all BC against dry plus wet removal was ∼4.7 days. About 90% of emitted FS BC mass was lost to internal mixing by coagulation, ∼7% to wet removal, ∼3% to dry removal, and a residual remaining airborne. Of all emitted plus internally mixed BC, ∼92% was wet removed and ∼8% dry removed, with a residual remaining airborne. The 20 and 100 year surface temperature response per unit continuous emissions (STRE) (similar to global warming potentials (GWPs)) of BC in FS were 4500-7200 and 2900―4600, respectively; those of BC in BSG were 2100―4000 and 1060-2020, respectively; and those of CH 4 were 52-92 and 29-63, respectively. Thus, FSBSG may be the second leading cause of warming after CO 2 . Controlling FS and BSG may be a faster method of reducing Arctic ice loss and global warming than other options, including controlling CH 4 or CO 2 , although all controls are needed.

Spatial and temporal distributions of U.S. winds and wind power at 80 m derived from measurements

windprofilesfromthesoundings,resultedin80-mwindspeedsthatare,onaverage,1.3–1.7 m/s faster than those obtained from the most common methods previously used to obtain elevated data for U.S. wind power maps, a logarithmic law and a power law, both with constant coefficients. The results suggest that U.S. wind power at 80 m may be substantially greater than previously estimated. It was found that 24% of all stations (and 37% of all coastal/offshore stations) are characterized by mean annual speeds � 6.9 m/s at 80 m, implying that the winds over possibly one quarter of the United States are strong enough to provide electric power at a direct cost equal to that of a new natural gas or coal power plant. ThegreatestpreviouslyunchartedreservoirofwindpowerinthecontinentalUnitedStatesis offshore and nearshore along the southeastern and southern coasts. When multiple wind sites are considered, the number of days with no wind power and the standard deviation of the wind speed, integrated across all sites, are substantially reduced in comparison with when one wind site is considered. Therefore a network of wind farms in locations with high annual mean wind speeds may provide a reliable and abundant source of electric power. INDEX TERMS: 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 3399 Meteorology and Atmospheric Dynamics: General or miscellaneous; 9350 Information Related to Geographic Region: North America;KEYWORDS:U.S. wind power, least squares, global warming, air pollution, energy, wind speed Citation: Archer, C. L., and M. Z. Jacobson, Spatial and temporal distributions of U.S. winds and wind power at 80 m derived from measurements, J. Geophys. Res., 108(D9), 4289, doi:10.1029/2002JD002076, 2003.