Assessment of the effect of air pollution controls on trends in shortwave radiation over the United States from 1995 through 2010 from multiple observation networks

Abstract. Long-term data sets of all-sky and clear-sky downwelling shortwave (SW) radiation, cloud cover fraction, and aerosol optical depth (AOD) were analyzed together with surface concentrations from several networks (e.g., Surface Radiation Budget Network (SURFRAD), Clean Air Status and Trend Network (CASTNET), Interagency Monitoring of Protection Visual Environments (IMPROVE) and Atmospheric Radiation Measurement (ARM)) in the United States (US). Seven states with varying climatology were selected to better understand the effects of aerosols and clouds on SW radiation. This analysis aims to assess the effects of reductions in anthropogenic aerosol burden resulting from substantial reductions in emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) over the past 16 yr across the US, based on trends in SW radiation. The SO2 and NOx emission data show decreasing trends from 1995 to 2010, which indirectly validates the effects of the Clean Air Act (CAA) in the US. Meanwhile, the total column AOD and surface total PM2.5 observations also show decreasing trends in the eastern US but slightly increasing trends in the western US. Moreover, measured surface concentrations of several other pollutants (i.e., SO2, SO4 and NOx) have similar behavior to AOD and total PM2.5. Analysis of the observed data shows strong increasing trends in all-sky downwelling SW radiation with decreasing trends in cloud cover. However, since observations of both all-sky direct and diffuse SW radiation show increasing trends, there may be other factors contributing to the radiation trends in addition to the decreasing trends in overall cloud cover. To investigate the role of direct radiative effects of aerosols, clear-sky downwelling radiation is analyzed so that cloud effects are eliminated. However, similar increasing trends in clear-sky total and diffuse SW radiation are observed. While significantly decreasing trends in AOD and surface PM2.5 concentrations along with increasing SW radiation (both all-sky and clear-sky) in the eastern US during 1995–2010 imply the occurrence of direct aerosol mediated "brightening", the increasing trends of both all-sky and clear-sky diffuse SW radiation contradicts this conclusion since diffuse radiation would be expected to decrease as aerosols direct effects decrease and cloud cover decreases. After investigating several confounding factors, the increasing trend in clear-sky diffuse SW may be due to more high-level cirrus from increasing air traffic over the US. The clear-sky radiation observations in the western US also show indications of "brightening" even though the AOD, PM2.5 and surface concentration do not vary drastically. This outcome was not unexpected because the CAA controls were mainly aimed at reducing air pollutant emissions in the eastern US and air pollutant levels in the western US were much lower at the onset. This suggests other factors affect the "brightening" especially in the western US.

[1]  V. Caron,et al.  United states. , 2018, Nursing standard (Royal College of Nursing (Great Britain) : 1987).

[2]  Ellsworth G. Dutton,et al.  Variability of the surface radiation budget over the United States from 1996 through 2011 from high‐quality measurements , 2013 .

[3]  Rohit Mathur,et al.  Historical gaseous and primary aerosol emissions in the United States from 1990 to 2010 , 2012 .

[4]  Elliot W. Martin,et al.  Long‐term trends in nitrogen oxide emissions from motor vehicles at national, state, and air basin scales , 2012 .

[5]  W. Malm,et al.  Particulate sulfate ion concentration and SO 2 emission trends in the United States from the early 1990s through 2010 , 2012 .

[6]  R. Gautam,et al.  Global and regional trends of aerosol optical depth over land and ocean using SeaWiFS measurements from 1997 to 2010 , 2012 .

[7]  J. Lelieveld,et al.  Trend analysis in aerosol optical depths and pollutant emission estimates between 2000 and 2009 , 2012 .

[8]  David M. Winker,et al.  Assessing boreal forest fire smoke aerosol impacts on U.S. air quality: A case study using multiple data sets , 2011 .

[9]  W. Malm,et al.  Uncertainties in PM2.5 Gravimetric and Speciation Measurements and What We Can Learn from Them , 2011, Journal of the Air & Waste Management Association.

[10]  Martin Wild,et al.  The roles of aerosol, water vapor and cloud in future global dimming/brightening , 2011 .

[11]  R. Mathur,et al.  WRF-CMAQ two-way coupled system with aerosol feedback: software development and preliminary results , 2011 .

[12]  T. Takemura,et al.  Large Asian dust layers continuously reached North America in April 2010 , 2011 .

[13]  Zbigniew Klimont,et al.  Anthropogenic sulfur dioxide emissions: 1850–2005 , 2010 .

[14]  U. Schumann,et al.  Global Modeling of the Contrail and Contrail Cirrus Climate Impact , 2010 .

[15]  Patrick Minnis,et al.  Contrails and Induced Cirrus: Optics and Radiation , 2010 .

[16]  Martin Wild,et al.  Global dimming and brightening: A review , 2009 .

[17]  Gert König-Langlo,et al.  Global dimming and brightening: An update beyond 2000 , 2009 .

[18]  Sally A. McFarlane,et al.  Significant decadal brightening of downwelling shortwave in the continental United States , 2009 .

[19]  R. Mathur.  Estimating the impact of the 2004 Alaskan forest fires on episodic particulate matter pollution over the eastern United States through assimilation of satellite‐derived aerosol optical depths in a regional air quality model , 2008 .

[20]  Leona Charles,et al.  Analysis of the Interaction of Aerosol Transport Layers on Local Air Quality , 2008, IGARSS 2008 - 2008 IEEE International Geoscience and Remote Sensing Symposium.

[21]  Christian Mätzler,et al.  Aerosol and cloud effects on solar brightening and the recent rapid warming , 2008 .

[22]  Joseph Michalsky,et al.  An aerosol optical depth climatology for NOAA's national surface radiation budget network (SURFRAD) , 2008 .

[23]  M. Haeffelin,et al.  Evaluation of cloudless‐sky periods detected by shortwave and longwave algorithms using lidar measurements , 2008 .

[24]  Charles N. Long,et al.  An Automated Quality Assessment and Control Algorithm for Surface Radiation Measurements , 2008 .

[25]  Mark D. Ivey,et al.  Quality Assurance of ARM Program Climate Research Facility Data , 2008 .

[26]  Robert S. Stone,et al.  Decadal variations in surface solar irradiance as observed in a globally remote network , 2006 .

[27]  David G. Streets,et al.  Two‐decadal aerosol trends as a likely explanation of the global dimming/brightening transition , 2006 .

[28]  Krista Gaustad,et al.  Estimation of fractional sky cover from broadband shortwave radiometer measurements , 2006 .

[29]  Joseph J. Michalsky,et al.  An Update on SURFRAD—The GCOS Surface Radiation Budget Network for the Continental United States , 2005 .

[30]  T. Stoffel,et al.  Solar and Infrared Radiation Station (SIRS) Handbook , 2005 .

[31]  C. Long,et al.  From Dimming to Brightening: Decadal Changes in Solar Radiation at Earth's Surface , 2005, Science.

[32]  U. Lohmann,et al.  Global indirect aerosol effects: a review , 2004 .

[33]  Martin Wild,et al.  On the consistency of trends in radiation and temperature records and implications for the global hydrological cycle , 2004 .

[34]  E. Dutton,et al.  Do Satellites Detect Trends in Surface Solar Radiation? , 2004, Science.

[35]  K. Gaustad,et al.  The Shortwave (SW) Clear-Sky Detection and Fitting Algorithm: Algorithm Operational Details and Explanations , 2004 .

[36]  B. Liepert,et al.  Observed reductions of surface solar radiation at sites in the United States and worldwide from 1961 to 1990 , 2002 .

[37]  Gerald Stanhill,et al.  Global dimming: a review of the evidence for a widespread and significant reduction in global radiation with discussion of its probable causes and possible agricultural consequences , 2001 .

[38]  C. Long,et al.  SURFRAD—A National Surface Radiation Budget Network for Atmospheric Research , 2000 .

[39]  C. Long,et al.  Identification of clear skies from broadband pyranometer measurements and calculation of downwelling shortwave cloud effects , 2000 .

[40]  Martin Wild,et al.  Means and Trends of Shortwave Irradiance at the Surface Estimated from Global Energy Balance Archive Data. , 1998 .

[41]  A. J. Miller,et al.  Factors affecting the detection of trends: Statistical considerations and applications to environmental data , 1998 .

[42]  J. Michalsky,et al.  Automated multifilter rotating shadow-band radiometer: an instrument for optical depth and radiation measurements. , 1994, Applied optics.