paleoenvironmental proxyan environmental relict (pollen grains, tree rings, lake sediments, pack rat middens, ice cores, coral skeletons) that is used by scientists to infer past…
parameterA value or measurement that varies with circumstances, and is used as a reference to quantify a situation or a process.
particle size distributionThe number of particles present in any given volume of air within a specified size range.
ParticulateA small, discrete mass of solid or liquid matter that remains individually dispersed in gas or liquid emissions.
Particulate Matter (PM)Very small pieces of solid or liquid matter such as particles of soot, dust, fumes, mists or aerosols.
ParticulatesThe fine liquid or solid particles contained in combustion gases. The quantity and size of particulates emitted by cars, power and industrial plants, wood…
Parts per billion (ppb)A measurement of concentration on a weight or volume basis. Equivalent to micrograms per liter.
Parts per million (ppm)A measurement of concentration on a weight or volume basis. Equivalent to milligrams per liter (mg/l).
Past weatherPast weather Predominant characteristic of the weather which had existed at an observing station during a given period of time (during the preceding hour…
Pentanes plusA mixture of hydrocarbons, mostly pentanes and heavier fractions, extracted from natural gas. See hydrocarbons.
Perfluorocarbons (PFCs)A group of human-made chemicals composed of carbon and fluorine only. These chemicals (predominantly CF4 and C2F6) were introduced as alternatives, along…
Petrochemical feedstockFeedstock derived from petroleum, used principally for the manufacture of chemicals, synthetic rubber, and a variety of plastics.
PetrochemicalsChemicals obtained by refining (i.e., distilling) crude oil. They are used as raw materials in the manufacture of most industrial chemicals, fertilizers…
PetroleumAny petroleum-based substance composed of a complex blend of hydrocarbons derived from crude oil, including motor fuel, jet oil, lubricants, petroleum…
Petroleum cokeA residue that is the final product of the condensation process in cracking.
PhotosynthesisA chemical process by which green plants synthesize organic compounds from carbon dioxide and water in the presence of sunlight.
Photovoltaic and solar thermal energyEnergy radiated by the sun as electromagnetic waves (electromagnetic radiation) that is converted into electricity by means of solar (i.e.
Pilot Balloon(Abbrev. PIBAL)- A small helium-filled meteorological balloon that is tracked as it rises through the atmosphere to determine how wind speed and direction…
Planetary Boundary LayerThe layer within the atmosphere between 1 km and the earth's surface where friction affects wind speed and wind direction.
PlanktonCollectively, all organisms (plants and animals) suspended in the water which are not independent of water movements.
planktonic foraminiferaMarine zooplankton that passively float or weakly swim, and have calcium carbonate skeletons that are present in large numbers on the surface of the ocean.
Pleistocene epochAn interval of the Quaternary period, from 1.8 million to about 11,500 years before present.
Point sourceAny discernible, confined, or discrete conveyance from which pollutants are or may be discharged, including, but not limited to, any pipe, ditch, channel…
Polar dayPolar day In polar regions, the portion of the year when the Sun is continuously in the sky.
Polar explorerPolar explorer A person working for a long time at one of the polar observing stations. Russian word is "polyarnik."
Polar lowPolar low Small, shallow depression which forms mainly in winter over some high-latitude seas within a polar or arctic air mass.
Polar nightPolar night In polar regions, the portion of the year when the Sun does not rise above the horizon.
Polar vortexPolar vortex Large-scale cyclonic circulation in the middle and upper troposphere centered generally in the polar regions.
PollutionA resource that is out of place. Generally, the presence of matter or energy whose nature, location or quantity produces undesired environmental effects.
Polyvinyl Chloride (PVC)A type of plastic used to make pipe and fittings for water distribution and irrigation.
Populationthe totality of items or units of material under consideration.
positive feedbackthe process in which an initial change will bring about an additional change in the same direction.
Potential TemperatureThe temperature a parcel of dry air would have if brought adiabatically (i.e., without transfer of heat or mass) to a standard pressure level of 1000 mb.
PrecessionThe comparatively slow torquing of the orbital planes of all satellites with respect to the Earth's axis, due to the bulge of the Earth at the equator…
precession (of the equinoxes)the slow clockwise motion of the equinoxes along the path of the earth's orbit due to the wobble of the earth's axis.
Precipitable WaterMeasure of the depth of liquid water at the surface that would result after precipitating all of the water vapor in a vertical column over a given…
PrecipitationThe total measurable amount of water received in the form of snow, rain, drizzle, hail, and sleet.
PrecisionThe accuracy with which a number can be represented, i.e., the number of digits used to represent a number.
preliminary dataData that have not necessarily been subjected to review, quality control and/or documentation by a responsible investigator.
Prescribed burningDeliberate setting and careful control of surface fires in forests to help prevent more destructive fires and to kill off unwanted plants that compete…
Present WeatherThe type of weather observed at the reporting time. These conditions may include types and intensity of precipitation such as light rain or heavy snow, as…
PressureThe load divided by the area over which it acts.
Pressure TendencyThe character and amount of atmospheric pressure change during a specified period of time, usually 3-hour period preceding an observation.
prevailing windThe wind direction most frequently observed during a given period.
Primary oil recoveryPumping out the crude oil that flows by gravity into the bottom of an oil well. See enhanced oil recovery, secondary oil recovery.
ProxyIf you own common stock in a US corporation, you have the right to vote on certain company policies and elect the board of directors by casting a proxy…
PsychrometerAn instrument for measuring relative humidity by means of wet and dry-bulb temperatures.
Psychrometric tablesPsychrometric tables Tables prepared from the psychrometric formula and used to obtain vapor pressure, relative humidity, and dew point from wet- and…
PyranometerA device used to measure total incident solar radiation (direct beam, diffuse, and reflected radiation) per unit time per unit area.