Nitrogen oxides (NOxNO+NO2) are produced during combustion processes and, thus may serve as a proxy for fossil fuel-based energy usage and committed greenhouse gases and other pollutants. We use ...high-resolution nitrogen dioxide (NO2) data from the Ozone Monitoring Instrument (OMI) to analyze changes in urban NO2 levels around the world from 2005 to 2014, finding complex heterogeneity in the changes. We discuss several potential factors that seem to determine these NOx changes. First, environmental regulations resulted in large decreases. The only large increases in the United States may be associated with three areas of intensive energy activity. Second, elevated NO2 levels were observed over many Asian, tropical, and subtropical cities that experienced rapid economic growth. Two of the largest increases occurred over recently expanded petrochemical complexes in Jamnagar (India) and Daesan (Korea). Third, pollution transport from China possibly influenced the Republic of Korea and Japan, diminishing the impact of local pollution controls. However, in China, there were large decreases over Beijing, Shanghai, and the Pearl River Delta, which were likely associated with local emission control efforts. Fourth, civil unrest and its effect on energy usage may have resulted in lower NO2 levels in Libya, Iraq, and Syria. Fifth, spatial heterogeneity within several megacities may reflect mixed efforts to cope with air quality degradation. We also show the potential of high-resolution data for identifying NOx emission sources in regions with a complex mix of sources. Intensive monitoring of the world's tropical subtropical megacities will remain a priority, as their populations and emissions of pollutants and greenhouse gases are expected to increase significantly.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Chinese COVID-19 policies indirectly lead to reduced fuel use and reduction in environmental emissions.
China’s policy interventions to reduce the spread of the coronavirus disease 2019 have ...environmental and economic impacts. Tropospheric nitrogen dioxide indicates economic activities, as nitrogen dioxide is primarily emitted from fossil fuel consumption. Satellite measurements show a 48% drop in tropospheric nitrogen dioxide vertical column densities from the 20 days averaged before the 2020 Lunar New Year to the 20 days averaged after. This decline is 21 ± 5% larger than that from 2015 to 2019. We relate this reduction to two of the government’s actions: the announcement of the first report in each province and the date of a province’s lockdown. Both actions are associated with nearly the same magnitude of reductions. Our analysis offers insights into the unintended environmental and economic consequences through reduced economic activities.
Nitrogen dioxide (NO2) is an important contributor to air pollution and can adversely
affect human health(1–9) . A decrease in NO2 concentrations has been reported as a result of lockdown measures to ...reduce the spread of COVID-19(10–20). Questions remain, however, regarding the relationship of satellite-derived atmospheric column NO2
data with health-relevant ambient ground-level concentrations, and the representativeness of limited ground-based monitoring data for global assessment.
Here we derive spatially resolved, global ground-level NO2 concentrations from NO2
column densities observed by the TROPOMI satellite instrument at sufficiently fine
resolution (approximately one kilometre) to allow assessment of individual cities
during COVID-19 lockdowns in 2020 compared to 2019. We apply these estimates to
quantify NO2 changes in more than 200 cities, including 65 cities without available
ground monitoring, largely in lower-income regions. Mean country-level
population-weighted NO2 concentrations are 29% ± 3% lower in countries with strict
lockdown conditions than in those without. Relative to long-term trends, NO2
decreases during COVID-19 lockdowns exceed recent Ozone Monitoring Instrument
(OMI)-derived year-to-year decreases from emission controls, comparable to 15 ± 4
years of reductions globally. Our case studies indicate that the sensitivity of NO2 to
lockdowns varies by country and emissions sector, demonstrating the critical need
for spatially resolved observational information provided by these satellite-derived
surface concentration estimates.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The TROPOspheric Monitoring Instrument (TROPOMI) is used to derive top-down NOX emissions for two large power plants and three megacities in North America. We first re-process the vertical column NO2 ...with an improved air mass factor to correct for a known systematic low bias in the operational retrieval near urban centers. For the two power plants, top-down NOX emissions agree to within 10% of the emissions reported by the power plants. We then derive top-down NOX emissions rates for New York City, Chicago, and Toronto, and compare them to projected bottom-up emissions inventories. In this analysis of 2018 NOX emissions, we find a +22% overestimate for New York City, a −21% underestimate in Toronto, and good agreement in Chicago in the projected bottom-up inventories when compared to the top-down emissions. Top-down NOX emissions also capture intraseasonal variability, such as the weekday versus weekend effect (emissions are +45% larger on weekdays versus weekends in Chicago). Finally, we demonstrate the enhanced capabilities of TROPOMI, which allow us to derive a NOX emissions rate for Chicago using a single overpass on July 7, 2018. The large signal-to-noise ratio of TROPOMI is well-suited for estimating NOX emissions from relatively small sources and for sub-seasonal timeframes.
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IJS, KILJ, NUK, PNG, UL, UM
We present a new and improved version (V4.0) of the NASA standard nitrogen
dioxide (NO2) product from the Ozone Monitoring Instrument (OMI) on the
Aura satellite. This version incorporates the most ...salient improvements for
OMI NO2 products suggested by expert users and enhances the NO2
data quality in several ways through improvements to the air mass factors
(AMFs) used in the retrieval algorithm. The algorithm is based on
the geometry-dependent surface Lambertian equivalent reflectivity (GLER)
operational product that is available on an OMI pixel basis. GLER is
calculated using the vector linearized discrete ordinate radiative transfer
(VLIDORT) model, which uses as input high-resolution bidirectional
reflectance distribution function (BRDF) information from NASA's Aqua
Moderate Resolution Imaging Spectroradiometer (MODIS) instruments over land
and the wind-dependent Cox–Munk wave-facet slope distribution over water,
the latter with a contribution from the water-leaving radiance. The GLER
combined with consistently retrieved oxygen dimer (O2–O2)
absorption-based effective cloud fraction (ECF) and optical centroid
pressure (OCP) provide improved information to the new NO2 AMF
calculations. The new AMFs increase the retrieved tropospheric NO2 by
up to 50 % in highly polluted areas; these differences arise from both
cloud and surface BRDF effects as well as biases between the new MODIS-based
and previously used OMI-based climatological surface reflectance data sets.
We quantitatively evaluate the new NO2 product using independent
observations from ground-based and airborne instruments. The new V4.0 data
and relevant explanatory documentation are publicly available from the NASA
Goddard Earth Sciences Data and Information Services Center (https://disc.gsfc.nasa.gov/datasets/OMNO2_V003/summary/, last access: 8 November 2020),
and we encourage their use over previous versions of OMI NO2 products.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
► Air pollution in China has created a substantial burden to its economy. ► Pollution-caused welfare damage increased from US$22 billion in 1975 to US$112 billion in 2005. ► Its relative magnitude ...declined from 14% of the historical level in 1975 to 5% in 2005. ► 29% of the 2005 pollution cost falls into the broader economic losses category.
This study evaluates air pollution-related health impacts on the Chinese economy by using an expanded version of the Emissions Prediction and Policy Analysis model. We estimated that marginal welfare impact to the Chinese economy of ozone and particulate-matter concentrations above background levels increased from 1997 US$22 billion in 1975 to 1997 US$112 billion in 2005, despite improvements in overall air quality. This increase is a result of the growing urban population and rising wages that thus increased the value of lost labor and leisure. In relative terms, however, welfare losses from air pollution decreased from 14% of the historical welfare level to 5% during the same period because the total size of the economy grew much faster than the absolute air pollution damages. In addition, we estimated that particulate-matter pollution alone led to a gross domestic product loss of 1997 US$64 billion in 1995. Given that the World Bank's comparable estimate drawn from a static approach was only 1997 US$34 billion, this result suggests that conventional static methods neglecting the cumulative impact of pollution-caused welfare damage are likely to underestimate pollution-health costs substantially. However, our analysis of uncertainty involved in exposure–response functions suggests that our central estimates are susceptible to significantly large error bars of around ±80%.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The Ozone Monitoring Instrument (OMI) onboard NASA's Aura satellite has been providing global observations of the ozone layer and key atmospheric pollutant gases, such as nitrogen dioxide (NO2) and ...sulfur dioxide (SO2), since October 2004. The data products from the same instrument provide consistent spatial and temporal coverage and permit the study of anthropogenic and natural emissions on local-to-global scales. In this paper, we examine changes in SO2 and NO2 over some of the world's most polluted industrialized regions during the first decade of OMI observations. In terms of regional pollution changes, we see both upward and downward trends, sometimes in opposite directions for NO2 and SO2, for different study areas. The trends are, for the most part, associated with economic and/or technological changes in energy use, as well as regional regulatory policies. Over the eastern US, both NO2 and SO2 levels decreased dramatically from 2005 to 2015, by more than 40 and 80 percent, respectively, as a result of both technological improvements and stricter regulations of emissions. OMI confirmed large reductions in SO2 over eastern Europe's largest coal-fired power plants after installation of flue gas desulfurization devices. The North China Plain has the world's most severe SO2 pollution, but a decreasing trend has been observed since 2011, with about a 50 percent reduction in 2012-2015, due to an economic slowdown and government efforts to restrain emissions from the power and industrial sectors. In contrast, India's SO2 and NO2 levels from coal power plants and smelters are growing at a fast pace, increasing by more than 100 and 50 percent, respectively, from 2005 to 2015. Several SO2 hot spots observed over the Persian Gulf are probably related to oil and gas operations and indicate a possible underestimation of emissions from these sources in bottom-up emission inventories. Overall, OMI observations have proved valuable in documenting rapid changes in air quality over different parts of the world during last decade. The baseline established during the first 11 years of OMI is indispensable for the interpretation of air quality measurements from current and future satellite atmospheric composition missions.
The nonlinear chemical processes involved in ozone production (P(O3)) have necessitated using proxy indicators to convey information about the primary dependence of P(O3) on volatile organic ...compounds (VOCs) or nitrogen oxides (NOx). In particular, the ratio of remotely sensed columns of formaldehyde (HCHO) to nitrogen dioxide (NO2) has been widely used for studying O3 sensitivity. Previous studies found that the errors in retrievals and the incoherent relationship between the column and the near-surface concentrations are a barrier in applying the ratio in a robust way. In addition to these obstacles, we provide calculational-observational evidence, using an ensemble of 0-D photochemical box models constrained by DC-8 aircraft measurements on an ozone event during the Korea-United States Air Quality (KORUS-AQ) campaign over Seoul, to demonstrate the chemical feedback of NO2 on the formation of HCHO is a controlling factor for the transition line between NOx-sensitive and NOx-saturated regimes. A fixed value (~2.7) of the ratio of the chemical loss of NOx (LNOx) to the chemical loss of HO2+RO2 (LROx) perceptibly differentiates the regimes. Following this value, data points with a ratio of HCHO/NO2 less than 1 can be safely classified as NOx-saturated regime, whereas points with ratios between 1 and 4 fall into one or the other regime. We attribute this mainly to the HCHO-NO2 chemical relationship causing the transition line to occur at larger (smaller) HCHO/NO2 ratios in VOC-rich (VOC-poor) environments. We then redefine the transition line to LNOx/LROx~2.7 that accounts for the HCHO-NO2 chemical relationship leading to HCHO = 3.7 × (NO2 – 1.14 × 1016 molec.cm-2). Although the revised formula is locally calibrated (i.e., requires for readjustment for other regions), its mathematical format removes the need for having a wide range of thresholds used in HCHO/NO2 ratios that is a result of the chemical feedback. Therefore, to be able to properly take the chemical feedback into consideration, the use of HCHO = a × (NO2 – b) formula should be preferred to the ratio in future works. We then use the Geostationary Trace gas and Aerosol Sensor Optimization (GeoTASO) airborne instrument to study O3 sensitivity in Seoul. The unprecedented spatial (250 × 250 m2) and temporal (~every 2 h) resolutions of HCHO and NO2 observations form the sensor enhance our understanding of P(O3) in Seoul; rather than providing a crude label for the entire city, more in-depth variabilities in chemical regimes are observed that should be able to inform mitigation strategies correspondingly.
•Ozone sensitivity over Seoul on an exceptionally degraded air quality day.•Various thresholds for HCHO/NO2 should be defined to label chemical regimes.•The inherent dependence of HCHO production on NOx levels complicates the ratio.•We redesign the formula to reflect the chemical feedback of NOx on HCHO.•GeoTASO provides in-depth variabilities in chemical regimes over Seoul.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Emissions of nitrogen oxides (NOx) and, subsequently, atmospheric levels of nitrogen dioxide (NO2) have decreased over the U.S. due to a combination of environmental policies and technological ...change. Consequently, NO2 levels have decreased by 30–40% in the last decade. We quantify NO2 trends (2005–2013) over the U.S. using surface measurements from the U.S. Environmental Protection Agency (EPA) Air Quality System (AQS) and an improved tropospheric NO2 vertical column density (VCD) data product from the Ozone Monitoring Instrument (OMI) on the Aura satellite. We demonstrate that the current OMI NO2 algorithm is of sufficient maturity to allow a favorable correspondence of trends and variations in OMI and AQS data. Our trend model accounts for the non-linear dependence of NO2 concentration on emissions associated with the seasonal variation of the chemical lifetime, including the change in the amplitude of the seasonal cycle associated with the significant change in NOx emissions that occurred over the last decade. The direct relationship between observations and emissions becomes more robust when one accounts for these non-linear dependencies. We improve the OMI NO2 standard retrieval algorithm and, subsequently, the data product by using monthly vertical concentration profiles, a required algorithm input, from a high-resolution chemistry and transport model (CTM) simulation with varying emissions (2005–2013). The impact of neglecting the time-dependence of the profiles leads to errors in trend estimation, particularly in regions where emissions have changed substantially. For example, trends calculated from retrievals based on time-dependent profiles offer 18% more instances of significant trends and up to 15% larger total NO2 reduction versus the results based on profiles for 2005. Using a CTM, we explore the theoretical relation of the trends estimated from NO2 VCDs to those estimated from ground-level concentrations. The model-simulated trends in VCDs strongly correlate with those estimated from surface concentrations (r = 0.83, N = 355). We then explore the observed correspondence of trends estimated from OMI and AQS data. We find a significant, but slightly weaker, correspondence (i.e., r = 0.68, N = 208) than predicted by the model and discuss some of the important factors affecting the relationship, including known problems (e.g., NOz interferents) associated with the AQS data. This significant correspondence gives confidence in trend and surface concentration estimates from OMI VCDs for locations, such as the majority of the U.S. and globe, that are not covered by surface monitoring networks. Using our improved trend model and our enhanced OMI data product, we find that both OMI and AQS data show substantial downward trends from 2005 to 2013, with an average reduction of 38% for each over the U.S. The annual reduction rates inferred from OMI and AQS measurements are larger (−4.8 ± 1.9%/yr, −3.7 ± 1.5%/yr) from 2005 to 2008 than 2010 to 2013 (−1.2 ± 1.2%/yr, −2.1 ± 1.4%/yr). We quantify NO2 trends for major U.S. cities and power plants; the latter suggest larger negative trend (−4.0 ± 1.5%/yr) between 2005 and 2008 and smaller or insignificant changes (−0.5 ± 1.2%/yr) during 2010–2013.
•Downward NO2 trends observed by OMI and surface measurements compare well.•Our improved OMI retrievals lead to a good agreement between AQS and OMI NO2 trends.•A trend model that accounts for a varying NO2 seasonality improves trend estimates.•Interference in surface measurements affects AQS-observed trends.•Satellite-observed trends complement and enrich the AQS-observed trends.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
TROPOspheric Monitoring Instrument (TROPOMI), on‐board the Sentinel‐5 Precurser satellite, is a nadir‐viewing spectrometer measuring reflected sunlight in the ultraviolet, visible, near‐infrared, and ...shortwave infrared. From these spectra several important air quality and climate‐related atmospheric constituents are retrieved, including nitrogen dioxide (NO2) at unprecedented spatial resolution from a satellite platform. We present the first retrievals of TROPOMI NO2 over the Canadian Oil Sands, contrasting them with observations from the Ozone Monitoring Instrument satellite instrument, and demonstrate TROPOMI's ability to resolve individual plumes and highlight its potential for deriving emissions from individual mining facilities. Further, the first TROPOMI NO2 validation is presented, consisting of aircraft and surface in situ NO2 observations, and ground‐based remote‐sensing measurements between March and May 2018. Our comparisons show that the TROPOMI NO2 vertical column densities are highly correlated with the aircraft and surface in situ NO2 observations, and the ground‐based remote‐sensing measurements with a low bias (15–30 %); this bias can be reduced by improved air mass factors.
Plain Language Summary
Nitrogen dioxide (NO2) is a pollutant that is linked to respiratory health issues and has negative environmental impacts such as soil and water acidification. Near the surface the most significant sources of NO2 are fossil fuel combustion and biomass burning. With a recently launched satellite instrument (TROPOspheric Monitoring Instrument TROPOMI), NO2 can be measured with an unprecedented combination of accuracy, spatial coverage, and resolution. This work presents the first TROPOMI NO2 measurements near the Canadian Oil Sands and shows that these measurements have an outstanding ability to detect NO2 on a very high horizontal resolution that is unprecedented for satellite NO2 observations. Further, these satellite measurements are in excellent agreement with aircraft and ground‐based measurements.
Key Points
First evaluation of the TROPOMI NO2 retrieval product
The quality of the TROPOMI NO2 data is excellent and captures variation on a very high spatial resolution
TROPOMI tropospheric NO2 retrievals can be corrected with higher‐resolution input data
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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