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Atmospheric pollutant concentrations expressed as mass per unit volume of atmospheric air (e.g., mg/m 3, μg/m 3, etc.) at sea level will decrease with increasing altitude because the atmospheric pressure decreases with increasing altitude. The change of atmospheric pressure with altitude can be obtained from this equation: [2]
mg/m 3 = milligrams of pollutant per cubic meter of air at sea level atmospheric pressure and T: ppmv = air pollutant concentration, in parts per million by volume T = ambient temperature in K = 273. + °C 0.082057338 = Universal gas constant in L atm mol −1 K −1: M = molecular mass (or molecular weight) of the air pollutant
Its units are in parts per million (ppm) for gases and in milligrams per cubic meter (mg/m 3) for particulates such as dust, smoke and mist. The basic formula for converting between ppm and mg/m 3 for gases is ppm = (mg/m^3) * 24.45 / molecular weight. This formula is not applicable to airborne particles.
Chemical regulation is sometimes [clarification needed] expressed in parts per million (ppm), but often [clarification needed] in milligrams per cubic meter (mg/m 3). [2] Units of measure for physical agents such as noise are specific to the agent.
where TDS is expressed in mg/L and EC is the electrical conductivity in microsiemens per centimeter at 25 °C. The conversion factor k e varies between 0.55 and 0.8. [5] Some TDS meters use an electrical conductivity measurement to the ppm using the above formula. Regarding units, 1 ppm indicates 1 mg of dissolved solids per 1,000 g of water. [6]
9 ppm Nitrogen dioxide 1 hour 0.12 ppm 1 year 0.03 ppm Ozone 1 hour 0.10 ppm 4 hours ... Units are in μg/m 3 except CO, which is in mg/m 3; IAQI SO 2, 24 hour
For chemicals, STEL assessments are usually done for 15 minutes and expressed in parts per million (ppm), or sometimes in milligrams per cubic meter (mg/m 3). [4] The American Conference of Governmental Industrial Hygienists publishes a more extensive list of STELs as threshold limit values (TLV-STEL). [5]
For carbon monoxide concentrations not exceeding 4 mg/m 3 24-hour mean. [ 2 ] Up to 30 % of Europeans living in cities are exposed to air pollutant levels exceeding EU air quality standards.