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Given hourly NOX and NO2 from a roadside site and hourly NOX, NO2 and O3 from a background site the function will estimate the emissions ratio of NO2/NOX --- the level of primary NO2


calcFno2(input, tau = 60, user.fno2, main = "", xlab = "year", ...)



A data frame with the following fields. nox andno2 (roadside NOX and NO2 concentrations), back_nox, back_no2 and back_o3 (hourly background concentrations of each pollutant). In addition temp (temperature in degrees Celsius) and cl (cloud cover in Oktas). Note that if temp and cl are not available, typical means values of 11 deg. C and cloud = 3.5 will be used.


Mixing time scale. It is unlikely the user will need to adjust this. See details below.


User-supplied f-NO2 fraction e.g. 0.1 is a NO2/NOX ratio of 10 series and is useful for testing "what if" questions.


Title of plot if required.


x-axis label.


Other graphical parameters send to scatterPlot.


As well as generating the plot itself, calcFno2 also returns an object of class ``openair''. The object includes three main components: call, the command used to generate the plot;

data, the data frame of summarised information used to make the plot; and plot, the plot itself. If retained, e.g. using

output <- calcFno2(...), this output can be used to recover the data, reproduce or rework the original plot or undertake further analysis.

An openair output can be manipulated using a number of generic operations, including print, plot and summary.


The principal purpose of this function is to estimate the level of primary (or direct) NO2 from road vehicles. When hourly data of NOX, NO2 and O3 are available, the total oxidant method of Clapp and Jenkin (2001) can be used. If roadside O3 measurements are available see linearRelation for details of how to estimate the primary NO2 fraction.

In the absence of roadside O3 measurements, it is rather more problematic to calculate the fraction of primary NO2. Carslaw and Beevers (2005c) developed an approach based on linearRelation the analysis of roadside and background measurements. The increment in roadside NO2 concentrations is primarily determined by direct emissions of NO2 and the availability of One to react with NO to form NO2. The method aims to quantify the amount of NO2 formed through these two processes by seeking the optimum level of primary NO2 that gives the least error.

Test data is provided at


Clapp, L.J., Jenkin, M.E., 2001. Analysis of the relationship between ambient levels of O3, NO2 and NO as a function of NOX in the UK. Atmospheric Environment 35 (36), 6391-6405.

Carslaw, D.C. and N Carslaw (2007). Detecting and characterising small changes in urban nitrogen dioxide concentrations. Atmospheric Environment. Vol. 41, 4723-4733.

Carslaw, D.C., Beevers, S.D. and M.C. Bell (2007). Risks of exceeding the hourly EU limit value for nitrogen dioxide resulting from increased road transport emissions of primary nitrogen dioxide. Atmospheric Environment 41 2073-2082.

Carslaw, D.C. (2005a). Evidence of an increasing NO2/NOX emissions ratio from road traffic emissions. Atmospheric Environment, 39(26) 4793-4802.

Carslaw, D.C. and Beevers, S.D. (2005b). Development of an urban inventory for road transport emissions of NO2 and comparison with estimates derived from ambient measurements. Atmospheric Environment, (39): 2049-2059.

Carslaw, D.C. and Beevers, S.D. (2005c). Estimations of road vehicle primary NO2 exhaust emission fractions using monitoring data in London. Atmospheric Environment, 39(1): 167-177.

Carslaw, D. C. and S. D. Beevers (2004). Investigating the Potential Importance of Primary NO2 Emissions in a Street Canyon. Atmospheric Environment 38(22): 3585-3594.

Carslaw, D. C. and S. D. Beevers (2004). New Directions: Should road vehicle emissions legislation consider primary NO2? Atmospheric Environment 38(8): 1233-1234.

See also

linearRelation if you have roadside ozone measurements.


David Carslaw


## Users should see the full openair manual for examples of how
## to use this function.