Desktop version

Home arrow Environment

  • Increase font
  • Decrease font


<<   CONTENTS   >>

Air Pollutants: Elevated Carbon Dioxide

Introduction....................................................................................................17

Atmospheric Change: Concentrations and Trends....................................17

Hans-Joachim Effects of °зand c°2 Alone.........................................................................18

Weigel and Interactive Effects of Air Pollutants and CO,.............................................19

Jurgen Bender CO, anc* * c°2 anti ot^er Air dilutants

Thiinen Institute Conclusion......................................................................................................21

of Biodiversity References........................................................................................................21

Introduction

The concentrations of various compounds in the atmosphere have changed during the last century, and they continue to change. Most of these compounds interact with the terrestrial biosphere as they are part of the overall biogeochemical cycling of, e.g., carbon, oxygen, nitrogen, and sulfur.111 For example, depending on their concentrations, gaseous compounds [sulfur dioxide (S02), nitrogen monoxide and dioxide (N02/N0)] may be beneficial to terrestrial ecosystems or remain inert (O,) at low concentrations, whereas at higher levels, they may act as air pollutants affecting these systems in an adverse manner. Although atmospheric C02 is the basic plant resource for photosynthesis, its current concentration is still limiting C3 plant growth. The rapid increase of the global atmospheric C02 concentration [C02], along with the overall changes in climate and atmospheric chemistry, require an assessment of the potential future interactive effects of air pollutants and elevated [C02] on terrestrial ecosystems.

Atmospheric Change: Concentrations and Trends

On a global scale, the concentrations of a variety of gaseous and particulate compounds in the atmosphere, including C02, N0/N02, S02, 03, ammonia (NH3), heavy metals, and volatile organic compounds (VOC) have undergone temporal and spatial changes during the last century.121 After peak emissions in the 1960s to the 1980s in industrialized countries particularly, the concentrations of S02, and to a smaller extent of NOx (N0/N02), VOCs, and particulate matter, have declined during the past decades in Europe and North America. NH3, which is the most important reduced N species, is of importance as a direct air pollutant in the vicinity of local emitters. However, wet and dry N deposition from oxidized and reduced N species are predicted to increase in other regions of the world.|3l The occurrence and distribution of airborne VOCs are difficult to assess because there are both anthropogenic and biogenic sources. With respect to heavy metals such as lead (Pb), cadmium (Cd), nickel (Ni), mercury (Hg), and zinc (Zn), a decline in emission and subsequent deposition was observed in most of Europe since the late 1980s. Unlike the development in Europe and North America, emissions and consequently atmospheric concentrations of many of the above-mentioned compounds have been increasing over the last two decades particularly in the rapidly growing regions of Asia, Africa, and Latin America.14! por example, China and India are now the leading emitters of S02 in the world. Also, the predicted further increase in global nitrogen oxide (NOx) emissions may be attributed largely to these countries. On the other hand, concentrations of ground-level 03 and atmospheric C02 have increased and continue to increase on a global scale. In most industrialized countries, 03 concentration [03] has nearly doubled during the last 100years. Current background [03] in the Northern hemisphere is within the range of 23-34 ppbv (parts-per-billion by volume). Although at least in most parts of Western Europe there is a clear trend of decreasing 03 peak values (“photosmog episodes”), models predict that background [O,] will continue to increase at a rate of 0.5% to 2% per year in the Northern Hemisphere during the next several decades, and that global surface [03] is expected to be in the range of 42-84 ppbv by 2100.151 O, pollution has also become a major environmental problem in many of the countries with rapidly developing population and related economic growth, respectively. 03 is currently considered the most important atmospheric pollutant that has direct negative effects on vegetation worldwide. Its concentrations vary considerably in time and space and show distinct annual and diurnal patterns.

Since the beginning of the 19th century, the C02 in the atmosphere has increased globally from approximately 280 ppmv (parts-per-million by volume) to current values of about 395 ppmv. It is expected that C02 will continue to increase even more rapidly and may reach about 550-650 ppmv between 2050 and 2070J61 C02 is the substrate for plant photosynthesis, and its current atmospheric concentration is limiting for photosynthesis and growth of C3 plants. It is expected that the increase in C02 will have far-reaching consequences for most types of vegetation.

 
<<   CONTENTS   >>

Related topics