Nitrogen dioxide (NO₂)

Nitrogen dioxide is a gaseous pollutant with acute (short term) and chronic (long term) effects on health, particularly in people with asthma. The government's Air Quality Strategy sets standards to protect against the effects of nitrogen dioxide (AQS 2000).

Empirical functions for NO2:NOX ratio (yield)

In managing nitrogen dioxide concentrations it is necessary to consider the total amount of oxides of nitrogen (NO_X), namely nitric oxide (NO) plus nitrogen dioxide (NO₂). Only a proportion of NO_X in the air will be present as NO₂. This proportion varies at different times according to chemical reactions in the air. The empirical work below can estimate the varying proportion or yield of NO₂. Concentrations are in units of ppb: i.e. parts per billion (parts per thousand million).

Dixon J, Middleton D R and Derwent R G (2001) Sensitivity of Nitrogen Dioxide concentrations to Oxides of Nitrogen controls in the United Kingdom Atmospheric Environment Vol 35/21 pp 3715-3728

Further references

Polynomial coefficients for estimating nitrogen dioxide concentrations

Our work on NO₂:NO_X began with a study of measurements taken in the Exhibition Road, South Kensington, London from 1991 and 1992 by Field, Goldstone and Lester at Imperial College as reported in Derwent et al. (1995). The hourly values were sorted into groups according to the amount of total oxides of nitrogen, or concentration of NO_X (ppb). A function was produced by curve-fitting on the bin-averages of the nitrogen dioxide values associated with the oxides of nitrogen in each bin. It was published in Clean Air by Derwent and Middleton (1996).

Our first function was limited to data from a single monitoring station over a limited period. There was also a need to assess the likely impact upon hourly mean concentrations of nitrogen dioxide, supposing additional restrictions on emissions of total oxides of nitrogen were introduced. Further work was funded at the Met Office by the Department of the Environment to investigate the function(s) best suited to a wider range of monitoring stations in the Department's monitoring network. The form of the polynomial was revised, and the curve-fitting was applied to values of the yield, defined as the ratio NO₂:NO_X. This dimensionless quantity is returned when the new polynomials are calculated. The yield is multiplied by NO_X in order to estimate NO₂.

Early results of the study looking at polynomials at several sites and monitoring years were outlined by Dixon, Middleton and Derwent (2000) at the 2nd Urban Air Quality conference in Madrid during 1999. The full results of the study were published by Dixon, Middleton and Derwent (2001).

Computer program YIELD31.FOR

Uses the polynomial coefficients from an input file to put calculated values of NO₂ for a user-selected site and year into the output file. It calculates the yield, slope and hourly NO₂. An output file and spreadsheet plot of the example function are included.

Computer program SOLVE41.FOR

Estimates the amount of NO_X control that is indicated by the polynomial in order to bring NO₂ down to some limit. This program was used in Dixon, Middleton and Derwent (2001).

 

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