Observing Requirements for Atmospheric Constituents

The observing requirements for atmospheric constituents were recommended by a sub-group of the AOPC that met in Toronto in May 1997. The list was agreed by the Third Session of the GCOS/WCRP Atmospheric Observation Panel for Climate, (Reading, UK, 19 - 22 August, 1997). The material below has been abstracted from the reports of AOPC meetings and the first draft of the AOPC Plan.

Measurements should focus on:

The directly climate relevant trace constituents such as H2O, CO2, O3, N2O, CH4, CFCs and their substitutes;
The indirectly radiatively centre species such as CO, VOC, NOx (NO, NOz). These species have important influence of the abundance of tropospheric OH, which determine the oxidation capacity of the troposphere and thus the distribution and abundance of several greenhouse gases.
Aerosols (and their precursors e.g., sulphate species) which influence the earth's radiation budget, both by direct effects, e.g., absorption and scattering as well as indirectly by contributing to changes of formation, distribution and type of clouds.
Radiation parameters including UV-D-radiation, global radiation, and photolysis rates e.g., for NO2 and O3.

For climate, the principal need is for climate forcing variables, biogeochemical cycles, trends, and fluxes at the boundaries.

Boundary layer and free air measurements are required both for monitoring and for model input and validation.

Specification of Parameters and Accuracies

The following information on requirements for chemical constituent observations is "Table 6.1. Important Climate-related Atmospheric Constituents" from the "GCOS Plan for Atmospheric Climate Observations", first draft. This table is still under development and should not be regarded as a final specification.

Constituent or Parameter	Altitude Region	Accuracy Rms	Accuracy Bias	Notes
*Greenhouse Gases, Water Vapor, Ozone*
Carbon Dioxide, CO2 (including isotopic composition)	All			Radiative forcing
Methane, CH4 (including isotopic composition)	All	10%	20% with continuity	Radiative forcing HOy chemistry; interpretation of H2O trend when measured simultaneously with H2O
Nitrous Oxide, N2O				Radiative forcing
Chlorofluorocarbons, CFCs (11, 12, 113)	All			Radiative forcing Lead to estimates of total inorganic Cl and total available Cl
Hydrochlorofluorocarbons, HCFCs (22, 141b, 142b)				Radiative forcing
Hydrofluorocarbons, HFCs (134a, 23)				Radiative forcing
Halons (1301, 1211, 2402, 1202)				Radiative forcing
Methyl Bromide, CH3Br	surface			Most abundant source gas for Bry
Fluorocarbons, CF4, C2F6
Methyl Chloroform, CH3CCl3
Sulphur Hexafluoride,SF6
Ozone, O3	column, profile	5%	1% with continuity	To assess changing effect on stratospheric forcing of climate Total column, profile, 3-D distribution; seasonal distribution Key regions for additional measurements are UT and LS, and in tropics High vertical resolution required at tropopause Ground-based, sonde and satellite instruments (aircraft obs. useful)
Water Vapour, H2O	1000-300hPa above	1% 5%	20% with continuity	The main greenhouse gas: controls radiation; 3-D distribution required; only 1 long-term record (30 years, Boulder) SPARC - stratospheric water vapour climatology Tropics is highest priority region
*AtmosphericAerosol*
Optical depth,				Properties needed to characterize aerosol and its effects;Some satellite observations available; routine observations in lower troposphere are limited and need improvement Still considered a research problem
Particle size,	profile
Chemical composition	profile
*Cloud*
High altitude cirrus				Trend in occurrence to assess radiative forcing changes
Contrails				Trend in occurrence to assess radiative forcing changes
Polar Stratospheric Clouds				Concern re decrease of temperature of lower stratosphere related to ozone depletion
*Radiation*
Solar constant	TOA			Evaluate changing total solar input
Solar flux spectrum(200-400nm)	TOA	0.1%		Monitor that part of the solar spectrum having most impact on stratosphere
UV at surface				Relate solar flux and total ozone change
*Species Important for Sources, Control and Understanding*
Bromine Monoxide plus Bromine Dioxide, BrOx	all	10%	20% with continuity	BrOx chemistry
Bromine Monoxide/ Hydrogen Bromide, BrO/HBr	column	10%	20% with continuity	BrOx chemistry
Hydroxyl plus Hydroperoxyl radicals, Hox	all	10%	20% with continuity	HOx chemistry
Total Chlorine, sum of Chlorine Monoxide, Chlorine Dioxide, Hydrochloric Acid and Chlorine Nitrate	all	10%	20% with continuity	To monitor decrease of total chlorine for Montreal Protocol (amended)
Chlorine Monoxide, ClO	all	10%	20% with continuity	Clx chemistry
Chlorine Dioxide, OClO	column	10%	20% with continuity	Clx and Brx chemistry
Hydrochloric Acid, HCl	all	10%	20% with continuity	Cly (reservoir species)
Chlorine Nitrate, ClONO2	all	10%	20% with continuity	Cly and NOy chemistry: the role of heterogeneous processes in the stratosphere (Cly reservoir)
Nitric Acid, HNO3	all	10%	20% with continuity	NOy chemistry (tracer)
Hydrogen Fluoride, HF
Carbon Monoxide, CO (including isotopic composition)
Nitric Oxide plus Nitrogen Dioxide, Nox	all	10%	20% with continuity	NOx chemistry
Non-methane Hydrocarbons, NMHCs
Volatile Organic Compounds, VOCs
Methyl Iodide, CH3I
Hydrogen Peroxide, H2O2
Peroxyacetyl Nitrate, PAN
Acetone, (CH3)2CO
Sulphur Dioxide, SO2
Dimethyl Sulphide, DMS
Carbonyl Sulphide, OCS	surface			precursor for background aerosol; indicator of trend in background aerosol



Facilitating Access to Global Observing Systems Data and Information

[ Home ] - [ Email GOSIC ]

Last Updated: Mar 7 2007				Copyright GOSIC 2006