title: Evaluation of an explicit NOxchemistry method in AERMOD.
abstract: An explicit NOxchemistry method has been implemented in AERMOD version 15181, ADMSM. The scheme has been evaluated by comparison with the methodologies currently recommended by the U.S. EPA for Tier 3 NO2calculations, that is, OLM and PVMRM2. Four data sets have been used for NO2chemistry method evaluation. Overall, ADMSM-modeled NO2concentrations show the most consistency with the AERMOD calculations of NOxand the highest Index of Agreement; they are also on average lower than those of both OLM and PVMRM2. OLM shows little consistency with modeled NOxconcentrations and markedly overpredicts NO2. PVMRM2 shows performance closer to that of ADMSM than OLM; however, its behavior is inconsistent with modeled NOxin some cases and it has less good statistics for NO2. The trend in model performance can be explained by examining the features particular to each chemistry method: OLM can be considered as a screening model as it calculates the upper bound of conversion from NO to NO2possible with the background O3concentration; PVMRM2 includes a much-improved estimate of in-plume O3but is otherwise similar to OLM, assuming instantaneous reaction of NO with O3; and ADMSM allows for the rate of this reaction and also the photolysis of NO2. Evaluation with additional data sets is needed to further clarify the relative performance of ADMSM and PVMRM2.
  
  
  
  Extensive evaluation of the current AERMOD Tier 3 chemistry methods OLM and PVMRM2, alongside a new scheme that explicitly calculates the oxidation of NO by O3and the reverse photolytic reaction, shows that OLM consistently overpredicts NO2concentrations. PVMRM2 performs well in general, but there are some cases where this method overpredicts NO2. The new explicit NOxchemistry scheme, ADMSM, predicts NO2concentrations that are more consistent with both the modeled NOxconcentrations and the observations.
authors.affiliation: a Cambridge Environmental Research Consultants , Cambridge , Cambridgeshire , United Kingdom.
authors.forename: David J
authors.initials: DJ
authors.lastname: Carruthers
authors.affiliation: a Cambridge Environmental Research Consultants , Cambridge , Cambridgeshire , United Kingdom.
authors.forename: Jenny R
authors.initials: JR
authors.lastname: Stocker
authors.affiliation: a Cambridge Environmental Research Consultants , Cambridge , Cambridgeshire , United Kingdom.
authors.forename: Andrew
authors.initials: A
authors.lastname: Ellis
authors.affiliation: a Cambridge Environmental Research Consultants , Cambridge , Cambridgeshire , United Kingdom.
authors.forename: Martin D
authors.initials: MD
authors.lastname: Seaton
authors.affiliation: a Cambridge Environmental Research Consultants , Cambridge , Cambridgeshire , United Kingdom.
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Smith
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D004784:Environmental Monitoring / Q000379:methods*; D008962:Models, Theoretical; D009569:Nitric Oxide / Q000737:chemistry*
chemical_list: D000393:Air Pollutants; D009569:Nitric Oxide