Chapter 4 of the IPCC Third Assessment Report Climate Change 2001: The Scientific Basis. Sections include: Executive Summary 2414.1 Introduction 2434.2 Trace Gases: Current Observations, Trends and Budgets 2484.3 Projections of Future Emissions 2664.4 Projections of Atmospheric Composition for the 21st Century 2674.5 Open Questions 2774.6 Overall Impact of Global Atmospheric Chemistry Change 279

/pdf/atmospheric-chemistry-and-greenhouse-gases-3uwk20zx33.pdf

Atmospheric chemistry and greenhouse gases

We present a summary of the latest measurements of ozone (03) and primary air pollutants at a rural/agricultural site in the fast developing Yangtze Delta region of China. The results of this study show elevated levels of primary pollutants (CO, SO2 and NO.*), which are about 1-5 times of those typically found in rural areas of North America and Europe. 03 pollution events are frequently observed. CO and SO2 levels are particularly high, resulting from the unique energy-use pattern in China. O3 shows strong positive correlation with NO.* and CO during periods of high photochemical activity. The O.-NO.* slope is comparable to the result from rural North America, but the O3-CO slope is substantially smaller for the Chinese site. With the anticipation of rapid changes of atmospheric composition in China, long-term measurements of key air pollutants will be necessary for documenting their trends and for studying their environmental impacts.

/pdf/ozone-and-related-gaseous-pollutants-in-the-boundary-layer-4xezedn2bm.pdf

Ozone and related gaseous pollutants in the boundary layer of eastern China: overview of the recent measurements at a rural site

As part of Maryland Aerosol Research and CHaracterization (MARCH-Atlantic) study, measurements of 24-hr average elemental carbon (EC) aerosol concentration were made at Fort Meade, Maryland, USA, a suburban site within the Baltimore-Washington corridor during July 1999, October 1999, January 2000, April 2000 and July 2000. Carbon monoxide (CO) and sulfur dioxide (SO2) were also measured nearly continuously over the period. Tight correlation between EC and CO in every month suggests common or proximate sources, likely traffic emissions. The EC versus CO slope varies in different seasons and generally increases with ambient temperature. The temperature dependence of EC/CO ratios suggests that EC source strength peaks in summer. By using the well established emission inventory for CO, and EC/CO ratio found in this study, EC emission over North America is estimated at 0.31±0.12 Tg yr−1, on the low end but in reasonable agreement with prior inventories based on emission factors and fuel consumption.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2000GL012354

Seasonal variations in elemental carbon aerosol, carbon monoxide and sulfur dioxide: Implications for sources

[1] Accurate emission inventories and their temporal trends must be incorporated into pollutant inventories to allow for reliable modeling of the country’s past, present, and future air quality. Measured carbon monoxide (CO) and nitrogen oxide (NOx) concentrations from two urban areas show that the CO/NOx vehicular emission ratio has decreased at an average rate of 7–9% per year from 1987 to 1999. This amounts to a factor of nearly 3 over the 12 years. The current U.S. Environmental Protection Agency tabulations of estimated pollutant emission trends indicate a rate of decrease smaller by a factor of 2–3. The trend in maximum ambient CO levels in U.S. cities suggests a 5.2 ± 0.8% per year average annual decrease in CO vehicular emissions, which implies a 2–3% annual increase in NOx emissions from vehicles. Thus over the decade of the 1990s, annual U.S. CO emissions from vehicles have decreased from 65 to 38 Tg, representing approximate decreases of 6 and 3% in the annual global fuel-use CO emissions and in total global anthropogenic CO emissions, respectively. It is expected that the volatile organic compound (VOC)/NOx vehicular exhaust emission ratio has decreased similarly, implying that the character of atmospheric photochemistry in U.S. urban areas has changed significantly over the decade. INDEX TERMS: 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; KEYWORDS: vehicle emissions, carbon monoxide, nitrogen oxides, emission inventories, temporal change

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2001JD000720

Decadal change in carbon monoxide to nitrogen oxide ratio in U.S. vehicular emissions

Research flights were conducted to investigate the episodic occurrence of enhanced ozone mixing ratios over the North Atlantic Ocean (NAO) during the spring as part of the Atmosphere/Ocean Chemistry Experiment (AEROCE). We measured meteorological variables, trace gases, and aerosol light scattering from the University of Wyoming King Air research aircraft during 16 research flights in April and early May 1996. The flights were conducted over eastern North America and over the NAO between the United States and Bermuda. On April 28, a cold front was located just west of Bermuda while a second system developed over the Midwest and central United States. In the midtroposphere, polluted layers with up to 250 ppbv CO, 150 pptv NO, and 1.8 ppbv NO y were observed within a deeper layer of enhanced O 3 mixing ratios (up to 88 ppbv) over the NAO at around 32°N, 64-68°W. These aircraft observations, when coupled with ozone sondes, back trajectories, and satellite image loops, indicate two distinct meteorological mechanisms that combine to yield the observed chemical signature of the air. There is substantial meteorological evidence, supported by ozone sonde observations and earlier King Air flights, indicating that stratosphere/troposphere exchange associated with the upstream frontal system injects and advects dry, ozone-rich air into midtro-pospheric regions over the continent. These subsiding air masses have the potential to result in deep layers of enhanced ozone in the offshore postfrontal area. Convection from the developing (upwind) system appears to lift air from the continental boundary layer into the area of subsidence in the mid to upper troposphere. The result is high concentrations of gaseous and particulate pollutants along with elevated quantities of ozone. Ozone mixing ratios exceed those attributable to boundary layer venting or in-transit photochemical production. These meteorological processes lead to pollution and enhanced ozone from the stratosphere cooccurring in postfrontal air masses over the NAO.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1999JD900444

Transport of ozone and pollutants from North America to the North Atlantic Ocean during the 1996 Atmosphere/Ocean Chemistry Experiment (AEROCE) intensive

Nearly continuous measurements of carbon monoxide (CO) were made at Shenandoah National Park-Big Meadows in rural Virginia, a site considered representative of regional air quality, from December 1994 to November 1997. Similar observations were also made at this location from October 1988 to October 1989. These observations combine to indicate a decreasing trend in CO concentration over the U.S. mid-Atlantic region of about 5.0 ppbv yr -1 , with greater than 95% confidence that the slope is significantly different from zero. The decrease suggests U.S. reductions in anthropogenic CO emissions have been effective in reducing pollutant levels. The observed trend is consistent with the U.S. EPA reported trend in emissions and the decrease in Northern Hemisphere tropospheric background CO mixing ratios observed by other researchers.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1999GL900609

Carbon monoxide in the U.S. mid-Atlantic troposphere: Evidence for a decreasing trend

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Carbon monoxide in the U.S. mid-Atlantic troposphere: Evidence for a decreasing trend