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Estimation Equations

1) Estimation Equations for Reactive Exposures and non-OH Chemistry

Estimation equations for OH exposure and for the exposure to non-OH reactants have been developed by the CU-Boulder group, and are summarized in Peng et al. (2016) for the low-NO modes and Peng et al. (2017) for the high-NO modes. We recommend the use of these equations during experimental planning, to avoid carrying out experiments under conditions where known problems can be significant or even dominant.

Equations have been developed for both the OFR185 and OFR254 modes of operation (under low-NO conditions), and the OFR185-cNO, OFR185-iN2O, and OFR254-iN2O modes (for trying to achieve high-NO conditions). We recommend that people always use the latest versions, which have additional diagnostics and bug fixes. Please read the instructions carefully before using it.

Note that it is almost impossible to achieve that goal (RO2 + NO dominates) by just introducing a lot of NO at he inlet of the OFR, as documented on Peng and Jimenez (2017)When studying sources with high NO, we recommend diluting by a significant factor (x100 is a typical number, though it'll vary with conditions) to get OHR close to ambient conditions. 

The spreadsheet and Igor program may be updated in the future as we receive feedback or implement other calculations, or if we receive bug reports. Please let us know of any suggestions or bugs by emailing and Any future updates will be posted here as well.

Applicability for different types of lamps
(1) The equations will work for OFR254 with any lamps (if using correct inputs)
(2) The equations will work for OFR185 with the "Penn State" lamps (model number inside the files)
(3) The equations will likely NOT work for OFR185 with the Aerodyne lamps. This is because the Aerodyne lamps have a very different F185/F254 ratio than the Penn State lamps, and the chemistry depends very strongly on that ratio. For the time being we don't have a solution for this problem. We hope to be able to report estimation equations in the future for OFR185 with the Aerodyne lamps, but there is not an explicit plan at this point.
(4) Note that we have also developed equations for OFR-i(iPrONO) and OFR-i(iPrONO-d7) with 369 nm lamps, included in Lambe et al. (2019). At present these equations are not included on the estimators listed in this page 

Release history:
  • v2.1 on Mar 30, 2016 (Excel only). This is the version released together with Peng et al. (2016)
  • v2.3 on Oct 12, 2016 (Excel and Igor). Added condition type plots to help the design of experiments avoiding impacts of non-OH chemistry. Fixed a small bug in the OFR254 O3 exposure cells.
  • v3.1 on Dec 4, 2017 (Excel and Igor). Added high NO modes. 
  • v3.3 on Jan 17, 2019 (Igor only). Added RO2 fate estimators (stand-alone, and integrated into OFR estimator)
  • Future work may include redoing all the equations for the Aerodyne lamps (pending characterization data from Aerodyne).
Publications describing the OFR kinetics model and its results
  • Li et al. 2015: first complete model of the radical chemistry for OFR185, controlling factors on OH exposure and OH suppression (Correction)
  • Peng et al. 2015: characterization of radical chemistry and OH exposure / suppression over a wide range of input conditions for OFR185 and OFR254 (Correction)
  • Peng et al. 2016: characterization of the impacts of non-OH chemistry for OFR185 and OFR254 (photolysis at 185 and 254 nm, O(1D), O(3P), O3, others)
  • Peng and Jimenez, ACP 2017: simulations of high iNO OFR modes
  • Peng et al., ACS E&SC 2018: simulations of the iN2O and cNO OFR modes
  • Lambe et al. 2019: simulations of the OFR-i(iPrONO) and related modes
  • Peng et al. 2019: fate of RO2 in different OFR modes compared to chambers & atmosphere
  • Please cite the relevant publications if using results from these calculators in publications and presentations. That will help us continue the development of these tools. For the low-NO exposure estimators, cite Peng et al. 2015 and 2016. For the high NO modes, cite Peng et al. 2017 and/or 2018, as applicable. For the RO2 exposure estimator cite Peng et al. 2019. 
2) Estimation Equations for LVOC Condensation Losses

A correction for the fraction of condensable species that do not condense onto particles within the OFR residence time ("LVOC fate correction") needs to be applied (or at least considered) for any experiments where quantification of aerosol formation in an OFR is required. A correction method has been developed by Palm et al. (2016), see Fig. 5 in that paper and associated discussion. This method was validated by analyzing the formation of SO2 --> Sulfate in the BEACHON-RoMBAS study (Fig. 6 in Palm et al. (2016)). A simple Igor function implementing the calculations from this method and showing results for example data is posted below. (If you don't use Igor, you can download a free Igor demo version from this page and use it to extract the code into a different program). We have added extensive comments in the source code, so between the function and the paper, the usage will hopefully be clear. Note that the parameters may be somewhat different for experimental setups very different from ours, but the structure of the method should still apply.

Please send any feedback and bug reports for the LVOC condensation code to and

If you use this function, please cite both Palm et al. (2016) and this page. If you modify or improve the function, please document it in a publication and share it by posting it to this page.

3) Comparison of Residence Time Distributions

You can download from below an Igor PXP that contains the graph comparing the residence time distributions published by Lambe et al. AMT (2011) for the PAM with the plate inlet, the Caltech flow reactor (Huang et al., AMT 2017) and the theoretical laminar profile. These were approximately digitized from the graphs using IgorThief. A version of this plot is shown in this AMTD comment (later updated to add plug flow and well-stirred reactor RTDs). It is posted here so that they can serve as a point of comparison for future RTDs measured by others for these and other flow reactors.

Jose-Luis Jimenez,
Oct 25, 2016, 10:01 PM
Jose-Luis Jimenez,
Oct 16, 2017, 6:23 AM
Jose-Luis Jimenez,
Dec 4, 2017, 3:35 PM
Jose-Luis Jimenez,
Dec 4, 2017, 3:35 PM
Jose-Luis Jimenez,
Jan 17, 2019, 5:07 PM
Jose-Luis Jimenez,
Jan 17, 2019, 5:07 PM
Jose-Luis Jimenez,
Jan 17, 2019, 5:07 PM