L. J. Mickley

Harvard University, Cambridge, Massachusetts, United States

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Publications (66)164.27 Total impact

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    ABSTRACT: Indonesia has experienced rapid land use change over the last few decades as forests and peatswamps have been cleared for more intensively managed land uses, including oil palm and timber plantations. Fires are the predominant method of clearing and managing land for more intensive uses, and the related emissions affect public health by contributing to regional particulate matter and ozone concentrations and global atmospheric carbon dioxide concentrations. Here, we examine emissions from fires associated with land use clearing and land management on the Indonesian island of Sumatra and the sensitivity of this fire activity to interannual meteorological variability. We find ~80% of 2005 to 2009 Sumatra emissions are associated with degradation or land use maintenance instead of immediate land use conversion, especially in dry years. We estimate Sumatra fire emissions from land use change and maintenance for the next two decades with five scenarios of land use change, the Global Fire Emissions Database Version 3, detailed 1-km2 land use change maps, and MODIS fire radiative power observations. Despite comprising only 16% of the original study area, we predict that 37-48% of future Sumatra emissions from land use change will occur in fuel-rich peatswamps unless this land cover type is protected effectively. This result means that the impact of fires on future air quality and climate in Equatorial Asia will be decided in part by the conservation status given to the remaining peatswamps on Sumatra. Results from this paper will be implemented in an atmospheric transport model to quantify the public health impacts from the transport of fire emissions associated with future land use scenarios in Sumatra.This article is protected by copyright. All rights reserved.
    Global Change Biology 07/2014; · 8.22 Impact Factor
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    ABSTRACT: The oxidative capacity of past atmospheres is highly uncertain. We present here a new climate-biosphere-chemistry modeling framework to determine oxidant levels in the present and past troposphere. We use the GEOS-Chem chemical transport model driven by meteorological fields from the NASA Goddard Institute of Space Studies (GISS) ModelE, with land cover and fire emissions from dynamic global vegetation models. We present time-slice simulations for the present day, late preindustrial era (AD 1770), and the Last Glacial Maximum (LGM, 19-23 ka), and we test the sensitivity of model results to uncertainty in lightning and fire emissions. We find that most preindustrial and paleo climate simulations yield reduced oxidant levels relative to the present day. Contrary to prior studies, tropospheric mean OH in our ensemble shows little change at the LGM relative to the preindustrial era (0.5 ± 12 %), despite large reductions in methane concentrations. We find a simple linear relationship between tropospheric mean ozone photolysis rates, water vapor, and total emissions of NOx and reactive carbon that explains 72 % of the variability in global mean OH in 11 different simulations across the last glacial-interglacial time interval and the industrial era. Key parameters controlling the tropospheric oxidative capacity over glacial-interglacial periods include overhead stratospheric ozone, tropospheric water vapor, and lightning NOx emissions. Variability in global mean OH since the LGM is insensitive to fire emissions. Our simulations are broadly consistent with ice-core records of Δ17O in sulfate and nitrate at the LGM, and CO, HCHO, and H2O2 in the preindustrial era. Our results imply that the glacial-interglacial changes in atmospheric methane observed in ice cores are predominantly driven by changes in its sources as opposed to its sink with OH.
    Atmospheric Chemistry and Physics 03/2014; 14(7). · 4.88 Impact Factor
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    ABSTRACT: Radiative forcing by aerosols and tropospheric ozone could play a significant role in recent Arctic warming. These species are in general poorly accounted for in climate models. We use the GEOS-Chem global chemical transport model to construct a 3-D representation of Arctic aerosols and ozone that is consistent with observations and can be used in climate simulations. We focus on 2008, when extensive observations were made from different platforms as part of the International Polar Year. Comparison to aircraft (ARCTAS), surface, and ship cruise (ICEALOT, ASCOS) observations suggests that GEOS-Chem provides in general a successful year-round simulation of Arctic black carbon (BC), organic carbon (OC), sulfate, and dust aerosol. BC has major fuel combustion and boreal fire sources, OC is mainly from fires, sulfate has a mix of anthropogenic and natural sources, and dust is mostly from the Sahara. The model is successful in simulating aerosol optical depth (AOD) observations from AERONET stations in the Arctic; the sharp drop from spring to summer appears driven in part by the smaller size of sulfate aerosol in summer. The anthropogenic contribution to Arctic AOD is a factor of 4 larger in spring than summer and is mainly sulfate. Simulation of absorbing aerosol optical depth (AAOD) indicates that non-BC aerosol (OC and dust) contributed 24% of Arctic AAOD at 550 nm and 37% of absorbing mass deposited to the snow pack in 2008. Open fires contributed half of AAOD at 550 nm and half of deposition to the snowpack.
    Journal of Geophysical Research: Atmospheres. 03/2014;
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    Xu Yue, Loretta J. Mickley, Jennifer A. Logan
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    ABSTRACT: We estimate area burned in southern California at mid-century (2046–2065) for the Intergovernmental Panel on Climate Change A1B scenario. We develop both regressions and a parameterization to predict area burned in three ecoregions, and apply present-day (1981–2000) and future meteorology from the suite of general circulation models to these fire prediction tools. The regressions account for the impacts of both current and antecedent meteorological factors on wildfire activity and explain 40–46 % of the variance in area burned during 1980–2009. The parameterization yields area burned as a function of temperature, precipitation, and relative humidity, and includes the impact of Santa Ana wind and other geographical factors on wildfires. It explains 38 % of the variance in area burned over southern California as a whole, and 64 % of the variance in southwestern California. The parameterization also captures the seasonality of wildfires in three ecoregions of southern California. Using the regressions, we find that area burned likely doubles in Southwestern California by midcentury, and increases by 35 % in the Sierra Nevada and 10 % in central western California. The parameterization suggests a likely increase of 40 % in area burned in southwestern California and 50 % in the Sierra Nevada by midcentury. It also predicts a longer fire season in southwestern California due to warmer and drier conditions on Santa Ana days in November. Our method provides robust estimates of area burned at midcentury, a key metric which can be used to calculate the fire-related effects on air quality, human health, and the associated costs.
    Climate Dynamics 02/2014; · 4.23 Impact Factor
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    ABSTRACT: Correlations between water cloud effective radius (CER) and aerosol optical depth (AOD) from the Moderate Resolution Imaging Spectroradiometer (MODIS) are examined over seven sub-regions in Eastern China for 2003–2012. Water phase cloud is defined as having a cloud top pressure greater than 800 hPa. Significant negative correlation coefficients (r = −0.79 ∼ −0.94) between AOD and CER are derived over the East Sea and the South China Sea for grid cells with AOD < 0.3. However, positive correlations (r = 0.01–0.91) are calculated for cells with AOD > 0.3. In contrast, significant positive correlations (r = 0.67–0.95) are derived over the Eastern China mainland and Yellow Sea. Further analysis for North China Plain shows that variations in wind speed and relative humidity may account for such positive correlations. Southerly winds carry high levels of pollutants and abundant water vapor, resulting in coincident increases in both AOD and CER in North China Plain, while the northerly winds transport dry and clean air from high latitudes, leading to decreases in AOD and CER. Both processes contribute to the positive correlations between AOD and CER over Eastern China, suggesting that the influence of background weather conditions need to be considered when studying the interactions between aerosol and cloud.
    Atmospheric Environment 02/2014; 84:244–253. · 3.11 Impact Factor
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    ABSTRACT: High smoke concentrations in Equatorial Asia, primarily from land conversion to oil palm plantations, affect a densely populated region and represent a serious but poorly quantified air quality concern. Continued expansion of the oil palm industry is expected but the resulting population exposure to smoke is highly dependent on where this expansion takes place. We use the adjoint of the GEOS-Chem chemical transport model to map the sensitivity of smoke concentrations in major Equatorial Asian cities, and for the population-weighted region, to the locations of the fires. We find that fires in southern Sumatra are particularly detrimental, and that a land management policy protecting peatswamp forests in Southeast Sumatra would be of great air quality benefit. Our adjoint sensitivities can be used to immediately infer population exposure to smoke for any future fire emission scenario.
    Atmospheric Environment. 01/2014;
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    Xu Yue, Loretta J Mickley, Jennifer A Logan, Jed O Kaplan
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    ABSTRACT: We estimate future wildfire activity over the western United States during the mid-21(st) century (2046-2065), based on results from 15 climate models following the A1B scenario. We develop fire prediction models by regressing meteorological variables from the current and previous years together with fire indexes onto observed regional area burned. The regressions explain 0.25-0.60 of the variance in observed annual area burned during 1980-2004, depending on the ecoregion. We also parameterize daily area burned with temperature, precipitation, and relative humidity. This approach explains ~0.5 of the variance in observed area burned over forest ecoregions but shows no predictive capability in the semi-arid regions of Nevada and California. By applying the meteorological fields from 15 climate models to our fire prediction models, we quantify the robustness of our wildfire projections at mid-century. We calculate increases of 24-124% in area burned using regressions and 63-169% with the parameterization. Our projections are most robust in the southwestern desert, where all GCMs predict significant (p<0.05) meteorological changes. For forested ecoregions, more GCMs predict significant increases in future area burned with the parameterization than with the regressions, because the latter approach is sensitive to hydrological variables that show large inter-model variability in the climate projections. The parameterization predicts that the fire season lengthens by 23 days in the warmer and drier climate at mid-century. Using a chemical transport model, we find that wildfire emissions will increase summertime surface organic carbon aerosol over the western United States by 46-70% and black carbon by 20-27% at midcentury, relative to the present day. The pollution is most enhanced during extreme episodes: above the 84(th) percentile of concentrations, OC increases by ~90% and BC by ~50%, while visibility decreases from 130 km to 100 km in 32 Federal Class 1 areas in Rocky Mountains Forest.
    Atmospheric Environment 10/2013; 77:767-780. · 3.11 Impact Factor
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    ABSTRACT: We use a global chemical transport model (GEOS-Chem) driven by the GISS GCM to investigate the effect on China's surface ozone from 2000 to 2050 global changes in climate and anthropogenic emissions as projected by the IPCC A1B scenario, with a focus on the different response between East and West China where present-day anthropogenic emissions, natural conditions, and ozone source attributions differ significantly. Over East China, climate change will increase both surface ozone and the possibility of high ozone episodes, implying a significant ‘climate change penalty’ that can be attributed mainly to increasing biogenic emissions of volatile organic compounds (VOCs). Over West China on the other hand, climate change will decrease mean surface ozone as a result of an increased ozone destruction rate in low-NOx regimes, assuming constant stratosphere–troposphere exchange (STE) of ozone. Chinese emissions change in 2050 will enlarge the East–West ozone difference in China, but emissions change from the rest of the world (excluding China) will decrease it. Driven by climate change and emissions change in combination, nation-mean surface ozone will increase, whereas East–West ozone contrast will decrease. In the future climate, the sensitivity of surface ozone to a given change in Chinese emissions will decrease over West China due to the accelerated ozone destruction rate and reduced transport from East China, but increase over East China as a result of the coupling effect between anthropogenic NOx and biogenic VOCs. The latter result suggests that the emission controls over East China need to be more aggressive in future climate.
    Atmospheric Environment 08/2013; 75:374–382. · 3.11 Impact Factor
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    ABSTRACT: [1] The inhibition of biogenic isoprene emission by elevated CO2 as observed in many plant taxa may significantly alter the sensitivity of air quality to global changes. We use a one-way coupled modeling framework to perform simulations under various combinations of 2000 to 2050 changes in climate, natural vegetation, anthropogenic emissions and land use to examine the effect of the CO2-isoprene interaction on atmospheric composition. We find that consideration of CO2 inhibition substantially reduces the sensitivity of surface ozone and secondary organic aerosol (SOA) to climate and natural vegetation, resulting in much smaller ozone and SOA increases in major populated regions than are projected by previous studies. The impact of land use on air quality is relatively insensitive to CO2 inhibition, rendering land use change the key factor that can offset or enhance the effects of anthropogenic emissions and shape air quality and climate-relevant species in the mid-21st century.
    Geophysical Research Letters. 07/2013; 40(13).
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    ABSTRACT: We investigate the 2000-2050 changes in concentrations of aerosols in China and the associated transboundary aerosol transport by using the chemical transport model GEOS-Chem driven by the Goddard Institute for Space Studies (GISS) general circulation model (GCM) 3 at 4° × 5° resolution. Future changes in climate and emissions projected by the IPCC A1B scenario are imposed separately and together through sensitivity simulations. Accounting for sulfate, nitrate, ammonium, black carbon (BC), and organic carbon (OC) aerosols, concentrations of individual aerosol species change by -2.3 to +1.7 μg m-3 and PM2.5 levels are projected to change by about 10-20% in eastern China as a result of 2000-2050 change in climate alone. With future changes in anthropogenic emissions alone, concentrations of sulfate, BC, and OC are simulated to decrease because of reductions in emissions, and those of nitrate are predicted to increase because of higher NOx emissions combined with decreases in sulfate. The net result is a reduction of seasonal mean PM2.5 concentrations in eastern China by 2-9.5 μg m-3 (or 10-30%) over 2000-2050. It is noted that current emission inventories for BC and OC over China are found to be inadequate at present. Transboundary fluxes of different aerosol species show different sensitivities to future changes in climate and emissions. The annual outflow of PM2.5 from eastern China to the western Pacific is estimated to change by -6.0%, -1.5%, and -9.0% over 2000-2050 owing to climate change alone, changes in emissions alone, and changes in both climate and emissions, respectively. The fluxes of nitrate and ammonium aerosols from Europe and Central Asia into western China increase over 2000-2050 by changes in emissions, leading to a 15% increase in annual inflow of PM2.5 to western China with future changes in both emissions and climate. Fluxes of BC and OC from South Asia to China in spring contribute to a large fraction of the annual inflow of PM2.5. The annual inflow of PM2.5 from South Asia and Southeast Asia to China is estimated to change by -55%, +133%, and +63% over 2000-2050 owing to climate change alone, changes in emissions alone, and changes in both climate and emissions, respectively. While the 4° × 5° spatial resolution is a limitation of the present study, the direction of predicted changes in aerosol levels and transboundary fluxes still provides valuable insight into future air quality.
    Atmospheric Chemistry and Physics 03/2013; 13(3):6501-6551. · 4.88 Impact Factor
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    A. P. K. Tai, L. J. Mickley, D. J. Jacob
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    ABSTRACT: Studies of the effect of climate change on fine particulate matter (PM2.5 air quality using general circulation models (GCMs) show inconsistent results including in the sign of the effect. This reflects uncertainty in the GCM simulations of the regional meteorological variables affecting PM2.5. Here we use the CMIP3 archive of data from fifteen different IPCC AR4 GCMs to obtain improved statistics of 21st-century trends in the meteorological modes driving PM2.5 variability over the contiguous US. We analyze 1999-2010 observations to identify the dominant meteorological modes driving interannual PM2.5 variability and their synoptic periods T. We find robust correlations (r > 0.5) of annual mean PM2.5 with T, especially in the eastern US where the dominant modes represent frontal passages. The GCMs all have significant skill in reproducing present-day statistics for T and we show that this reflects their ability to simulate atmospheric baroclinicity. We then use the local PM2.5-to-period sensitivity (dPM2.5/dT) from the 1999-2010 observations to project PM2.5 changes from the 2000-2050 changes in T simulated by the 15 GCMs following the SRES A1B greenhouse warming scenario. By weighted-average statistics of GCM results we project a likely 2000-2050 increase of ~ 0.1 μg m-3 in annual mean PM2.5 in the eastern US arising from less frequent frontal ventilation, and a likely decrease albeit with greater inter-GCM variability in the Pacific Northwest due to more frequent maritime inflows. Potentially larger regional effects of 2000-2050 climate change on PM2.5 may arise from changes in temperature, biogenic emissions, wildfires, and vegetation, but are still unlikely to affect annual PM2.5 by more than 0.5 μg m-3.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 12/2012; 12(23):11329-11337. · 5.51 Impact Factor
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    ABSTRACT: We present a new model for the global tropospheric chemistry of inorganic bromine (Bry) coupled to oxidant-aerosol chemistry in the GEOS-Chem chemical transport model (CTM). Sources of tropospheric Bry include debromination of sea-salt aerosol, photolysis and oxidation of short-lived bromocarbons, and transport from the stratosphere. Comparison to a GOME-2 satellite climatology of tropospheric BrO columns shows that the model can reproduce the observed increase of BrO with latitude, the northern mid-latitudes maximum in winter, and the Arctic maximum in spring. This successful simulation is contingent on the HOBr + HBr reaction taking place in aqueous aerosols and ice clouds. Bromine chemistry in the model decreases tropospheric ozone mixing ratios by <1-8 nmol mol-1 (6.5% globally), with the largest effects in the northern extratropics in spring. The global mean tropospheric OH concentration decreases by 4%. Inclusion of bromine chemistry improves the ability of global models (GEOS-Chem and p-TOMCAT) to simulate observed 19th-century ozone and its seasonality. Bromine effects on tropospheric ozone are comparable in the present-day and pre-industrial atmospheres so that estimates of anthropogenic radiative forcing are minimally affected. Br atom concentrations are 40% higher in the pre-industrial atmosphere due to lower ozone, which would decrease by a factor of 2 the atmospheric lifetime of elemental mercury against oxidation by Br. This suggests that historical anthropogenic mercury emissions may have mostly deposited to northern mid-latitudes, enriching the corresponding surface reservoirs. The persistent rise in background surface ozone at northern mid-latitudes during the past decades could possibly contribute to the observations of elevated mercury in subsurface waters of the North Atlantic.
    Atmospheric Chemistry and Physics 08/2012; 12(15):6723-6740. · 5.51 Impact Factor
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    A. P. K. Tai, L. J. Mickley, D. J. Jacob
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    ABSTRACT: Studies of the effect of climate change on fine particulate matter (PM2.5) air quality using general circulation models (GCMs) have yielded inconsistent results including in the sign of the effect. This reflects uncertainty in the GCM simulations of the regional meteorological variables affecting PM2.5. Here we use the CMIP3 archive of data from fifteen different IPCC AR4 GCMs to obtain improved statistics of 21st-century trends in the meteorological modes driving PM2.5 variability over the contiguous US. We analyze 1999-2010 observations to identify the dominant meteorological modes driving interannual PM2.5 variability and their synoptic periods T. We find robust correlations (r > 0.5) of annual mean PM2.5 with T, especially in the Eastern US where the dominant modes represent frontal passages. The GCMs all have significant skill in reproducing present-day statistics for T and we show that this reflects their ability to simulate atmospheric baroclinicity. We then use the local PM2.5-to-period sensitivity (dPM2.5/dT) from the 1999-2010 observations to project PM2.5 changes from the 2000-2050 changes in T simulated by the 15 GCMs following the SRES A1B greenhouse warming scenario. By weighted-average statistics of GCM results we project a likely 2000-2050 increase of ~0.1 μg m-3 in annual mean PM2.5 in the Eastern US arising from less frequent frontal ventilation, and a likely decrease of ~0.3 μg m-3 in the Northwestern US due to more frequent maritime inflows. These circulation-driven changes are relatively small. Potentially larger regional effects of 2000-2050 climate change on PM2.5 may arise from changes in temperature, biogenic emissions, wildfires, and vegetation, but are still unlikely to affect annual PM2.5 by more than 0.5 μg m-3.
    Atmospheric Chemistry and Physics 07/2012; 12(7):18107-18131. · 4.88 Impact Factor
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    ABSTRACT: Projecting the effects of climate change on fine particulate matter (PM2.5) air quality requires an understanding of the relationships of PM2.5 with meteorological variables. We used a multiple linear regression model to correlate both observed and model simulated daily mean concentrations of total PM2.5 and its components with meteorological variables in the contiguous US for 2004-2008. All data were deseasonalized to focus on synoptic-scale correlations. We observe strong positive correlations of all PM2.5 components with temperature in most of the US, except for nitrate in the Southeast where the correlation is negative. Relative humidity (RH) is generally positively correlated with sulfate and nitrate but negatively correlated with organic carbon. We find that most of the correlations of PM2.5 with temperature and RH do not arise from direct dependence on these variables but largely from covariation with synoptic transport. We thus applied principal component analysis and regression to identify the dominant meteorological modes controlling PM2.5 variability, and show that 20-40% of the observed PM2.5 day-to-day variability can be explained by a single dominant meteorological mode: cold frontal passages in the eastern US and maritime inflows in the West, both associated with the movement of synoptic weather systems. These and other synoptic transport modes are found to contribute to most of the overall correlations of PM2.5 with temperature and RH except in the Southeast. We further show that the observed annual mean PM2.5 in the Midwest for 1999-2010 is strongly anticorrelated with cyclone frequencies as diagnosed from a spectral-autoregressive analysis of the dominant meteorological mode, with a PM2.5-to-cyclone sensitivity of -0.075±0.036 μg m-3 a (Figure). From this sensitivity and a trend analysis of future climate model outputs we project a 0.22±0.68 μg m-3 increase in annual mean PM2.5 in the Midwest in the 2050's climate due to a reduction in cyclone frequencies. Our results point to the dominance of synoptic weather systems in controlling PM2.5 variability, and the importance of cyclone frequency as the major climate variable for PM2.5 air quality.
    AGU Fall Meeting Abstracts. 12/2011;
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    ABSTRACT: We use a general circulation model (NASA Goddard Institute for Space Studies GCM 3) to investigate the regional climate response to removal of aerosols over the United States. We perform a pair of transient 2010–2050 climate simulations following a scenario of increasing greenhouse gas concentrations, with and without aerosols over the United States and with present-day aerosols elsewhere. We find that removing U.S. aerosol significantly enhances the warming from greenhouse gases in a spatial pattern that strongly correlates with that of the aerosol. Warming is nearly negligible outside the United States, but annual mean surface temperatures increase by 0.4–0.6 K in the eastern United States. Temperatures during summer heat waves in the Northeast rise by as much as 1–2 K due to aerosol removal, driven in part by positive feedbacks involving soil moisture and low cloud cover. Reducing U.S. aerosol sources to achieve air quality objectives could thus have significant unintended regional warming consequences.
    Atmospheric Environment 12/2011; · 3.11 Impact Factor
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    ABSTRACT: We applied a multiple linear regression model to understand the relationships of PM2.5 with meteorological variables in the contiguous US and from there to infer the sensitivity of PM2.5 to climate change. We used 2004-2008 PM2.5 observations from ~1000 sites (~200 sites for PM2.5 components) and compared to results from the GEOS-Chem chemical transport model (CTM). All data were deseasonalized to focus on synoptic-scale correlations. We find strong positive correlations of PM2.5 components with temperature in most of the US, except for nitrate in the Southeast where the correlation is negative. Relative humidity (RH) is generally positively correlated with sulfate and nitrate but negatively correlated with organic carbon. GEOS-Chem results indicate that most of the correlations of PM2.5 with temperature and RH do not arise from direct dependence but from covariation with synoptic transport. We applied principal component analysis and regression to identify the dominant meteorological modes controlling PM2.5 variability, and show that 20-40% of the observed PM2.5 day-to-day variability can be explained by a single dominant meteorological mode: cold frontal passages in the eastern US and maritime inflow in the West. These and other synoptic transport modes drive most of the overall correlations of PM2.5 with temperature and RH except in the Southeast. We show that interannual variability of PM2.5 in the US Midwest is strongly correlated with cyclone frequency as diagnosed from a spectral-autoregressive analysis of the dominant meteorological mode. An ensemble of five realizations of 1996-2050 climate change with the GISS general circulation model (GCM) using the same climate forcings shows inconsistent trends in cyclone frequency over the Midwest (including in sign), with a likely decrease in cyclone frequency implying an increase in PM2.5. Our results demonstrate the need for multiple GCM realizations (because of climate chaos) when diagnosing the effect of climate change on PM2.5, and suggest that analysis of meteorological modes of variability provides a computationally more affordable approach for this purpose than coupled GCM-CTM studies.
    Atmospheric Chemistry and Physics 11/2011; 11(11):31031-31066. · 4.88 Impact Factor
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    ABSTRACT: Anthropogenic emissions of nitrogen oxides (NOx ≡ NO + NO2) and carbon monoxide (CO) affect particulate matter (PM) air quality on an intercontinental scale by changing background concentrations of oxidants (OH, ozone, H2O2) and thus increasing the oxidation rate of sulfur dioxide (SO2) to sulfate and NOx to nitrate. We conduct sensitivity simulations with the GEOS–Chem chemical transport model and find that these intercontinental influences of NOx and CO emissions on PM can be greater than those from SO2 emissions (a direct PM precursor). The intercontinental impact of oxidant precursors is greatest in receptor regions with high domestic SO2, NOx, and ammonia emissions and hence already high levels of PM. US NOx and CO emissions increase annual mean PM in northern Europe and eastern China by up to 0.25 μg m−3. The increase in Europe is mostly as sulfate, whereas in China it is mostly as nitrate. East Asian NOx and CO emissions have a weaker intercontinental influence (∼0.2 μg m−3 in northern Europe, ∼0.1 μg m−3 in the eastern US). These intercontinental effects of NOx and CO emissions on PM depend in a complex way on the chemical environment of receptor regions. Intercomparison of results from different models would be of great interest.Highlights► Aerosol formation is enhanced by distant NOx and CO emissions. ► NOx and CO emissions affect intercontinental PM air quality more than SO2. ► Intercontinental effect of NOx and CO is largest where air quality is already poor.
    Atmospheric Environment 01/2011; 45(19):3318-3324. · 3.11 Impact Factor
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    S. Wu, L. J. Mickley, J. O. Kaplan, D. J. Jacob
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    ABSTRACT: The effects of future land use and land cover change on the chemical composition of the atmosphere and air quality are largely unknown. To investigate the potential effects associated with future changes in vegetation driven by atmospheric CO2 concentrations, climate, and anthropogenic land use over the 21st century, we performed a series of model experiments combining a general circulation model with a dynamic global vegetation model and an atmospheric chemical-transport model. Our results indicate that climate- and CO2-induced changes in vegetation composition and density could lead to decreases in summer afternoon surface ozone of up to 10 ppb over large areas of the northern mid-latitudes. This is largely driven by the substantial increases in ozone dry deposition associated with changes in the composition of temperate and boreal forests where conifer forests are replaced by those dominated by broadleaf tree types, as well as a CO2-driven increase in vegetation density. Climate-driven vegetation changes over the period 2000-2100 lead to general increases in isoprene emissions, globally by 15 % in 2050 and 36 % in 2100. These increases in isoprene emissions result in decreases in surface ozone concentrations where the NOx levels are low, such as in remote tropical rainforests. However, over polluted regions, such as the northeastern United States, ozone concentrations are calculated to increase with higher isoprene emissions in the future. Increases in biogenic emissions also lead to higher concentrations of secondary organic aerosols, which increase globally by 10 % in 2050 and 20 % in 2100. Surface concentrations of secondary organic aerosols are calculated to increase by up to 1 mug m-3 for large areas in Eurasia. When we use a scenario of future anthropogenic land use change, we find less increase in global isoprene emissions due to replacement of higher-emitting forests by lower-emitting cropland. The global atmospheric burden of secondary organic aerosols changes little by 2100 when we account for future land use change, but both secondary organic aerosols and ozone show large regional changes at the surface.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2011; 11:15469-15495. · 5.51 Impact Factor
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    ABSTRACT: We investigate the climate response to US anthropogenic aerosol sources over the 1950 to 2050 period by using the NASA GISS general circulation model (GCM) and comparing to observed US temperature trends. Time-dependent aerosol distributions are generated from the GEOS-Chem chemical transport model applied to historical emission inventories and future projections. Radiative forcing from US anthropogenic aerosols peaked in 1970-1990 and has strongly declined since due to air quality regulations. We find that the regional radiative forcing from US anthropogenic aerosols elicits a strong regional climate response, cooling the central and eastern US by 0.5-1.0 °C on average during 1970-1990, with the strongest effects on maximum daytime temperatures in summer and autumn. Aerosol cooling reflects comparable contributions from direct and indirect (cloud-mediated) radiative effects. Absorbing aerosol (mainly black carbon) has negligible warming effect. Aerosol cooling reduces surface evaporation and thus decreases precipitation along the US east coast, but also increases the southerly flow of moisture from the Gulf of Mexico resulting in increased cloud cover and precipitation in the central US. Observations over the eastern US show a lack of warming in 1960-1980 followed by very rapid warming since, which we reproduce in the GCM and attribute to trends in US anthropogenic aerosol sources. Present US aerosol concentrations are sufficiently low that future air quality improvements are projected to cause little further warming in the US (0.1 °C over 2010-2050). We find that most of the potential warming from aerosol source controls in the US has already been realized over the 1980-2010 period.
    Atmospheric Chemistry and Physics 01/2011; 11:24127-24164. · 4.88 Impact Factor
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    Y. F. Lam, J. S. Fu, Wu S, L. J. Mickley
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    ABSTRACT: Simulations of present and future average regional ozone and PM2.5 concentrations over the United States were performed to investigate the potential impacts of global climate change and emissions on regional air quality using CMAQ. Various emissions and climate conditions with different biogenic emissions and domain resolutions were implemented to study the sensitivity of future air quality trends from the impacts of changing biogenic emissions. A comparison of GEOS-Chem and CMAQ was performed to investigate the effect of downscaling on the prediction of future air quality trends. For ozone, the impacts of global climate change are relatively smaller when compared to the impacts of anticipated future emissions reduction, except for the Northeast area, where increasing biogenic emissions due to climate change have stronger positive effects (increases) to the regional ozone air quality. The combination effect from both climate change and emission reductions leads to approximately a 10% or 5 ppbv decrease of the maximum daily average eight-hour ozone (MDA8) over the Eastern United States. For PM2.5, the impacts of global climate change have shown insignificant effect, where as the impacts of anticipated future emissions reduction account for the majority of overall PM2.5 reductions. The annual average 24-h PM2.5 of the future-year condition was found to be about 40% lower than the one from the present-year condition, of which 60% of its overall reductions are contributed to by the decrease of SO4 and NO3 particulate matters. Changing the biogenic emissions model increases the MDA8 ozone by about 5–10% or 3–5 ppbv in the Northeast area. Conversely, it reduces the annual average PM2.5 by 5% or 1.0 μg/m3 in the Southeast region.
    Atmospheric Chemistry and Physics 01/2011; · 4.88 Impact Factor