Source contributions to United States ozone and particulate matter over five decades from 1970 to 2020
Introduction
Since the 1970 Clean Air Act, the U.S. Environmental Protection Agency (EPA) has regulated US criteria air pollutants to improve air quality, visibility and acid deposition. Major regulations include passenger vehicle emission controls for nitrogen oxide (NOx), volatile organic compounds (VOCs) and carbon monoxide (CO), which have tightened progressively from Tier 0 through Tier 3 (EPA, 2016a), New Source Performance Standards for industrial sources affecting VOC, NOx, CO, sulfur dioxide (SO2), and particulate matter (PM) emissions from specific stationary source categories (EPA, 2016b), the Acid Rain Program covering major SOx and NOx sources such as electric utilities (EPA, 2016c), the NOx SIP Call (Federal Register, 1998), to name a few. Previous studies have evaluated long-term trends in air quality and emissions in the US to demonstrate the effectiveness of emission reductions strategies (Simon et al., 2014, Blanchard et al., 2010, Butler et al., 2011, Sather and Cavender, 2012, Hidy and Blanchard, 2015). This information can help in guiding future air quality management plans. The planning in many cases can be complicated by non-controllable factors including intercontinental transport (Jaffe et al., 2003, Lin et al., 2012), meteorology influences (Camalier et al., 2007, Cox and Chu, 1996, Lin et al., 2015), as well as interactions among reacting species.
Impacts from intercontinental transport to U.S. air quality depend on emissions in other regions in the world which have changed significantly in the last five decades. Europe has taken extensive measures to reduce emissions which have resulted in a reduction of pollution recorded between 1980 and 2000 (Lovblad et al., 2004). However, fast growing economies contribute to increased emissions in parts of Asia (Streets and Waldhoff, 2000, Akimoto, 2003, Richter et al., 2005). Such spatial changes in global emissions can potentially change background pollution levels in different regions of US, thus they need to be considered when evaluating U.S. trends. In fact, evidence has suggested recent increase of foreign contributions in the U.S. (Parrish et al., 2009, Parrish et al., 2012, Cooper et al., 2012, Gratz et al., 2015). Therefore, an accurate description of temporal and spatial variations at regional and global scales in long-term emissions inventories is crucial in trend studies.
Air quality models (AQMs) have been increasingly used to demonstrate effectiveness of control scenarios and long-range transport. AQMs can overcome some deficiencies of spatial and temporal data of ambient monitoring networks. For example, Hogrefe et al. (2009) simulated PM2.5 over the northeastern United States for 1988–2005 and integrated with observations to provide greater spatial coverage and speciation information in addition to total mass. AQMs can also help separate the effects of intercontinental transport and domestic contributions (Dolwick et al., 2015, Wild et al., 2012, Hogrefe et al., 2004). To date, most AQM applications in the U.S. are applied for short episodes or single years (Goldberg et al., 2016, Dolwick et al., 2015, Nopmongcol et al., 2014 to name a few). Only a few have extended to multi-years (Bouchet et al., 1999, Pierce et al., 2010, Godowitch et al., 2010, Hogrefe et al., 2011, Xing et al., 2015). Most recent air quality modeling by Xing et al. (2015) applied a regional model with 108 × 108 km resolution across the northern hemisphere over 1990–2010 period. Their trends represent sub-grid variability as well as changes in local emissions. While such an approach allows a direct comparison to observations, it cannot separate effects of changes in local and global emissions to US air quality, which are important to air quality planners.
We focus on how changing global and local emissions influence air quality rather than the effects of inter-annual meteorological variation or long-term climate change. A clear focus on the influence of emission trends can provide useful information to motivate needed inventory improvements. Meteorological changes can mask the trend attributable to changes in precursor emissions (Lin et al., 2015). For this reason the meteorology is held constant (for 2005) and there are no changes to meteorology-dependent emissions (e.g., vegetation, from fires). Air quality planners in the U.S. use the same approach to assess how changes in local emissions influence Ozone (O3) and PM2.5. We simulate intercontinental transport with global emissions and characterize regional changes in O3 and PM2.5 due to the intercontinental transport and local emissions representing six years within five decades (1970–2020). We track contributions from each source sector and each US region throughout the five decades.
Section snippets
Air quality modeling
We use CAMx version 6.1 (ENVIRON, 2014) with the 2005 version of the Carbon Bond chemical mechanism (CB05; Yarwood et al., 2005) to simulate O3 and PM2.5 with anthropogenic emissions for 1970, 1980, 1990, 2000, 2005, and 2020 using the model configurations described in Nopmongcol et al. (2016). The meteorology and all natural emissions, including wild fires, are held constant for 2005 to isolate the effect of changing anthropogenic emissions outside the US. The modeling domain has 36 km
Changes in U.S. emissions of O3 and PM2.5 precursors
U.S. emissions decline from 1970 to 2020 (Table 1; 2020 numbers are based on projections) for all pollutants although at varying rates. Emission totals for the top 5 source categories are provided as Supplemental Information (Figure S2). NOx emissions decline by 59% from 1970 to 2020. Tightening on-road vehicle emission standards reduce NOx emissions from 1980 onward but growing vehicle miles travelled keep on-road vehicles as the largest NOx contributor. EGUs are the second highest NOx
Summary and conclusions
We model O3 and PM2.5 across the U.S. for 2005 meteorological conditions and vary anthropogenic emissions in the U.S. and worldwide from 1970 to 2020. To promote consistent results for this extended time period, during which inventory methods improved, we develop U.S. anthropogenic emission inventories specifically for this study to minimize effects of changing methods. We fix the meteorological year and the natural emissions at 2005 to isolate effects of changing anthropogenic emissions alone.
Acknowledgements
This work was supported by the Electric Power Research Institute.
References (59)
- et al.
NMOC, ozone and organic aerosol in the southeastern states. 1999–2007: 2. Ozone trends and sensitivity to NMOC emissions in Atlanta, Georgia
Atmos. Environ.
(2010) - et al.
Response of ozone and nitrate to stationary source NOx emission reductions in the eastern USA
Atmos. Environ.
(2011) - et al.
The effects of meteorology on ozone in urban areas and their use in assessing ozone trends
Atmos. Environ.
(2007) - et al.
Assessment of interannual ozone variation in urban areas from a climatological perspective
Atmos. Environ.
(1996) - et al.
Comparison of background ozone estimates over the western United States based on two separate model methodologies
Atmos. Environ.
(2015) - et al.
Assessment of the effects of horizontal grid resolution on long-term air quality trends using coupled WRF-CMAQ simulations
Atmos. Environ.
(2016) - et al.
Assessing multi-year changes in modeled and observed urban NOx concentrations from a dynamic model evaluation perspective
Atmos. Environ.
(2010) - et al.
Causes of increasing ozone and decreasing carbon monoxide in springtime at the Mt. Bachelor Observatory from 2004 to 2013
Atmos. Environ.
(2015) - et al.
A combined model–observation approach to estimate historic gridded fields of PM 2.5 mass and species concentrations
Atmos. Environ.
(2009) - et al.
Six new episodes of trans-Pacific transport of air pollutants
Atmos. Environ.
(2003)
Implementation and evaluation of PM 2.5 source contribution analysis in a photochemical model
Atmos. Environ.
A modeling analysis of alternative primary and secondary US ozone standards in urban and rural areas
Atmos. Environ.
Changes in US background ozone due to global anthropogenic emissions from 1970 to 2020
Atmos. Environ.
Dynamic evaluation of a regional air quality model: assessing the emissions-induced weekly ozone cycle
Atmos. Environ.
The relation between ozone, NOx and hydrocarbons in urban and polluted rural environments
Atmos. Environ.
Present and future emissions of air pollutants in China: SO2, NOx, and CO
Atmos. Environ.
Global air quality and pollution
Science
Studying ozone climatology with a regional climate model: 2
Climatol. J. Geophys. Res.
LEV 3 Inventory Database Tool version 9h. November
Long-term ozone trends at rural ozone monitoring sites across the United States, 1990–2010
J. Geophys. Res.
Source apportionment of the anthropogenic increment to ozone, formaldehyde, and nitrogen dioxide by the path-integral method in a 3D model
Environ. Sci. Technol.
Comparison of source apportionment and source sensitivity of ozone in a three-dimensional air quality model
Environ. Sci. Technol.
The Emissions Database for Global Atmospheric Research
User's Guide: Comprehensive Air Quality Model with Extensions (CAMx)
Guidance for Regulatory Application of the Urban Airshed Model (UAM)
Methods Used to Estimate Emissions, 1900-1984: National Air Pollutant Emission Trends Document, Procedures Report, 1900-1996
Procedures Document for National Emission Inventory
Technical Support Document (TSD) for the Final Transport Rule [EPA-HQ-OAR-2009-0491]
Emission Standards for Light-duty Vehicles and Trucks
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2022, Atmospheric EnvironmentCitation Excerpt :Nopmongcol et al. (2017a, see Fig. 6 therein) also report that area source (equivalent to “other area” plus “dust” in this study) makes the largest contribution to annual average PM2.5 in 2020 at all nine select cities, while the second ranking sector varies among EGU, off-road, non-EGU and on-road sources across the cities. Similarly, Nopmongcol et al. (2017a) find a significant decline in the on-road contribution to PM2.5 from 2005 to 2020. The above findings suggest that further reduction of PM2.5 in the future is more dependent on controls of “other area”, “dust”, “other point” and “non-road” sources.