Can someone help me to summirize this article. Here is the direct link for this

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Can someone help me to summirize this article. Here is the direct link for this website. https://www.sciencedaily.com/releases/2017/11/171106121306.htm

And please this my last remaining question for this period, I don't have anymore. I need someone who can help me with this article. Thank you

The top row of images show each region in 2005, which had abundant NOx in urban areas where human emissions are high, leading to systems where ozone formation was controlled by VOC amounts. As pollution controls were put into place on NOx emissions, by 2015, the systems in Europe, the United States, and East Asian urban areas became limited by NOx, meaning that further controls on NOx would help reduce ozone formation. With the industrial growth of the last decade, the results in China outside the major cities show an increase in areas transitioning to being controlled by VOC amounts.

Credit: NASA

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The top row of images show each region in 2005, which had abundant NOx in urban areas where human emissions are high, leading to systems where ozone formation was controlled by VOC amounts. As pollution controls were put into place on NOx emissions, by 2015, the systems in Europe, the United States, and East Asian urban areas became limited by NOx, meaning that further controls on NOx would help reduce ozone formation. With the industrial growth of the last decade, the results in China outside the major cities show an increase in areas transitioning to being controlled by VOC amounts.

Credit: NASA

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Ozone pollution near Earth's surface is one of the main ingredients of summertime smog. It is also not directly measurable from space due to the abundance of ozone higher in the atmosphere, which obscures measurements of surface ozone. New NASA-funded research has devised a way to use satellite measurements of the precursor gases that contribute to ozone formation to differentiate among three different sets of conditions that lead to its production. These observations may also assist air quality managers in assessing the most effective approaches to emission reduction programs that will improve air quality.

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Unlike its presence at high altitude where ozone acts as Earth's sunscreen from harmful ultraviolet radiation, at low altitudes, ozone is a health hazard contributing to respiratory problems like asthma and bronchitis. It is formed through complex chemical reactions initiated by sunlight and involving two types of gases, volatile organic compounds (VOC) and nitrogen oxides (NOx). Both are represented in the study by a major gas of each type, the VOC formaldehyde and NO2, that are measureable from space by the Dutch-Finnish Ozone Monitoring Instrument aboard NASA's Aura satellite, launched in 2004.

"We're using satellite data to analyze the chemistry of ozone from space," said lead author Xiaomeng Jin at the Lamont-Doherty Earth Observatory at Columbia University in Palisades, New York. Their research was published in Journal of Geophysical Research: Atmospheres, a publication of the American Geophysical Union.

With a combination of computer models and space-based observations, she and her colleagues used the concentrations of ozone's precursor molecules to infer whether ozone production increases more in the presence of NOx, VOCs, or a mix of the two, for a given location. Their study regions focused on North America, Europe and East Asia during the summer months, when abundant sunlight triggers the highest rates of ozone formation. To understand their impact on ozone formation, Jin and her team investigated whether VOC or NOx was the ingredient that most limited ozone formation. If emissions of that molecule are reduced, then ozone formation will be reduced -- critical information for air quality managers.

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"We are asking, 'If I could reduce either VOCs or NOx, which one is going to get me the biggest bang for my buck in terms of the amount of ozone that we can prevent from being formed in the lower atmosphere?'" said co-author and atmospheric chemist Arlene Fiore at Lamont-Doherty, who is also a member of NASA's Health and Air Quality Applied Sciences Team that partially funded this work and fosters collaboration between scientists and air quality managers.

The findings show that cities in North America, Europe and East Asia, are more often VOC-limited or in a transitional state between VOC and NOx-limited. In addition, the 12-year data record of satellite observations show that a location's circumstances can change. For instance, in 2005 New York City's ozone production during the warm season was limited by VOCs, but by 2015 it had transitioned to a NOx-limited system due to reduced NOx emissions resulting from controls put into place at both regional and national levels. This transition means that future NOx reductions will likely further decrease ozone production, said Jin.

Volatile organic compounds occur in high volume naturally, given off by some plants, including certain tree species. They can also arise from paint fumes, cleaning products, and pesticides, and are a by-product of burning fossil fuels in factories and automobiles. Nitrogen oxides are a byproduct of burning fossil fuels and are abundant in cities, produced by power plants, factories, and cars. Because VOCs have a large natural source during summer over the eastern United States, for example, emission reduction plans over the last two decades in this region have focused on NOx, which is overwhelmingly produced by human activities.

Space-based methods for monitoring ozone chemistry complement surface-based measurements made by air quality management agencies. The view from space offers consistent coverage of broad areas, and provides data for regions that may not have ground stations.

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The ozone hole over Antarctica shrunk to its smallest maximum-extent in September 2017. Here, in this false-color view of the monthly-averaged total ozone the blue and purple indicate areas with the least ozone, while yellows and reds mean the most ozone.

Higher temperatures over Antarctica this year shrank the hole in the ozone layer to the smallest it's been since 1988.

Explanation / Answer

OMI observations of NO2 and HCHO column densities, along with a global chemical transport model (GEOS-Chem) to examine the sensitivities of surface O3 pollution to NOx and VOC emissions over northern mid-latitude source regions. GEOSChem model is used to determine the regime thresholds for FNR with two emission perturbation simulations. Surface FNR in the model does indicate surface O3 sensitivity, and that regionally constant FNR thresholds can separate the NOx-limited and NOx-saturated conditions to at least 90% confidence. FNR values marking the boundaries of the photochemical regimes are derived from the model, and thus depend on the mechanism used to represent photochemistry. Travis et al. [2016] suggest an overestimate of NOx emissions over the eastern U.S.A. Such an overestimate could lead to excessive tropospheric NO2 columns as well as an underestimate of d[O3]/dENOx, which may largely cancel out so that the threshold values would be less sensitive to this error. Erroneously high NO2 columns, however, could lead us to diagnose excessively low regime threshold values over NOxsaturated regions. Column FNR shows a lower regime classification accuracy, largely due to variations in column-to-surface relationships. The column-to-surface relationships for NO2 correlate strongly with PBLH, but weakly for HCHO. As a result, the column-to-surface relationship of FNR (fc_s) is inversely correlated with PBLH. Following the spatial and temporal variations of PBHL, fc_s shows pronounced seasonal cycles with maxima in winter and minima in summer, which act to dampen the spatial and temporal variation of surface O3 sensitivity. We adjust the regime threshold values for column-based FNR using the modeled fc_s. The derived column FNR thresholds marking the boundaries between ozone production regimes vary by a factor of 3 over North America and Europe. The modeled vertical profiles are also sensitive to the PBL scheme. Full PBL mixing scheme is implemented in GEOSChem. The full-mixing scheme in GEOS-Chem is likely to underestimate the vertical gradient of both NO2 and HCHO [Lin et al., 2010; Zhang et al., 2016]. Even though modeled FNR can indicate surface O3 sensitivity to NOx vs. VOC precursors, both satellite-derived and modeled FNR are subject to uncertainties. We compare four combinations of two OMI HCHO products (BIRA, SAO) and OMI NO2 (DP, SP) products with GEOS-Chem simulations. The spatial and temporal correlation between the modeled and observed indicator ratios depends on the choice of NO2 product, while the mean bias depends on the choice of HCHO product. We note that wintertime satellite retrievals of HCHO incur large uncertainties due to diminished satellite sensitivity near the surface [De Smedt et al., 2015]. Qualitatively, however, such uncertainties should not affect the conclusion that ozone production is NOx-saturated in winter over regions heavily influenced by anthropogenic emissions, as noted in previous studies [Kleinman, 1991, 1994; Jacob et al., 1995]. Satellite-derived O3 sensitivity generally agree with in situ observations performed in previous studies. While the distinct behavior of indicator ratio over urban and rural environment cannot be fully resolved from the coarse resolution of global model, the finer resolution of OMI observation can explain the majority of the spatial and temporal variation © 2017 American Geophysical Union. All rights reserved. of O3 sensitivity. Future work could assess the ability of the OMI indicator ratio to reveal urban fine-scale features with a higher resolution (e.g., regional) model. Combining model-derived threshold values with a decadal record of satellite observations, we further investigate how O3 production sensitivity to precursors has changed over the 2005 to 2015 period. We find a general increase in FNROMI over the urban areas of North America, Europe, South Korea and Japan from 2005 to 2015, driven by NOx emission reductions imposed over the past decade. The spring transition to a NOx-limited regime has shifted earlier in some megacities, and the NOx-limited regime has become dominant in summer. China shows an overall decrease in FNROMI except for the most developed areas such as Beijing, Shanghai and Pearl River Delta, where emission control strategies have been implemented. In our FNR analysis, HCHO serves as an indicator of reactivity-weighed VOCs, but the yield and production of HCHO from isoprene is non-linearly dependent on the NOx level [Wolfe et al., 2016]; this non-linearity implies that FNR may underestimate increases in NOx sensitivity as NOx emissions decline. Surface O3 sensitivity also varies throughout the day and from day to day. The suitability of the FNROMI for daily variation is still limited by the uncertainties associated with the OMI HCHO and NO2 retrievals. In addition, the spatial resolution of OMI may be too coarse to reveal VOC-limited chemistry in urban cores. Near-term advances in spacebased observations of HCHO and NO2 from geostationary satellites as anticipated to occur over East Asia (Geostationary Environment Monitoring Spectrometer), Europe (Sentinel-4) and North America (Tropospheric Emissions: Monitoring of Pollution) [Lahoz et al., 2012], offer exciting opportunities to explore the potential for space-based FNR to diagnose ozone production regimes at finer spatial and temporal scales.

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