2 Ozone in the Eastern United States: Production Efficiency Variability …
11
organic nitrate, nitric acid, nitrous acid, nitrate radical, aerosol nitrate, and dinitrogen
pentoxide as N).
A second estimate of OPE applies ratios of O 3 sensitivities (S [ppb]) to mobile
and electricity generating unit (EGU) emissions:
O P E
N O DE P
=
S O 3 ,M O B + S O 3 ,EGU
S N O Z ,M O B + S N O Z ,EGU
(2.2)
This equation directly estimates the ratio of O 3 attributable to major emissions
sources to NO Z attributable to the same sources. It does, however, omit effects of
differing O 3 and NO Z deposition rates, which we rectify by adding source-specific
deposition sensitivities (e.g., S
DE P
O 3 ,M O B ):
O P E =
S O 3 ,M O B + S
DE P
O 3 ,M O B
+
S O 3 ,EGU + S
DE P
O 3 ,EGU
S N O Z ,M O B + S
DE P
N O Z ,M O B
+
S N O Z ,EGU + S
DE P
N O Z ,EGU
(2.3)
where S
DE P
i, j
[ppb] is the sensitivity of species i deposition to emissions from source
j and must be calculated from CMAQ output S
DE P
∗
i,j
[kg km
2 ]. This is achieved by
dividing S
DE P
∗
i,j
by total deposition (DE P
∗
i [kg]) and multiplying by concentration
[ppb].
The form of Eq. 2.3 can be further refined to calculate source-specific OPE:
O P E M O B =
S O 3 ,M O B + S
DE P
O 3 ,M O B
S N O Z ,M O B + S
DE P
N O Z ,M O B
(2.4)
O P E EGU =
S O 3 ,EGU + S
DE P
O 3 ,EGU
S N O Z ,EGU + S
DE P
N O Z ,EGU
(2.5)
2.2.2 Observation-Based OPE
Long-term detailed observation records from the Southeastern Aerosol Research and
Characterization (SEARCH) network were used to estimate OPE at eight urban and
rural sites. OPE was calculated by regressing average 2–3 pm O 3 concentrations
against NO Z concentrations at each site. To assess only air parcels with similar
histories, only days with photochemical state (PS*, a measure of the atmosphere’s
emissions-independent reactivity described in detail by Henneman et al. [4]) in the
80th percentile were included in the regressions. Fits were assessed using a flexible
spline model to capture increasing OPEs at lower NO Z concentrations.
11
organic nitrate, nitric acid, nitrous acid, nitrate radical, aerosol nitrate, and dinitrogen
pentoxide as N).
A second estimate of OPE applies ratios of O 3 sensitivities (S [ppb]) to mobile
and electricity generating unit (EGU) emissions:
O P E
N O DE P
=
S O 3 ,M O B + S O 3 ,EGU
S N O Z ,M O B + S N O Z ,EGU
(2.2)
This equation directly estimates the ratio of O 3 attributable to major emissions
sources to NO Z attributable to the same sources. It does, however, omit effects of
differing O 3 and NO Z deposition rates, which we rectify by adding source-specific
deposition sensitivities (e.g., S
DE P
O 3 ,M O B ):
O P E =
S O 3 ,M O B + S
DE P
O 3 ,M O B
+
S O 3 ,EGU + S
DE P
O 3 ,EGU
S N O Z ,M O B + S
DE P
N O Z ,M O B
+
S N O Z ,EGU + S
DE P
N O Z ,EGU
(2.3)
where S
DE P
i, j
[ppb] is the sensitivity of species i deposition to emissions from source
j and must be calculated from CMAQ output S
DE P
∗
i,j
[kg km
2 ]. This is achieved by
dividing S
DE P
∗
i,j
by total deposition (DE P
∗
i [kg]) and multiplying by concentration
[ppb].
The form of Eq. 2.3 can be further refined to calculate source-specific OPE:
O P E M O B =
S O 3 ,M O B + S
DE P
O 3 ,M O B
S N O Z ,M O B + S
DE P
N O Z ,M O B
(2.4)
O P E EGU =
S O 3 ,EGU + S
DE P
O 3 ,EGU
S N O Z ,EGU + S
DE P
N O Z ,EGU
(2.5)
2.2.2 Observation-Based OPE
Long-term detailed observation records from the Southeastern Aerosol Research and
Characterization (SEARCH) network were used to estimate OPE at eight urban and
rural sites. OPE was calculated by regressing average 2–3 pm O 3 concentrations
against NO Z concentrations at each site. To assess only air parcels with similar
histories, only days with photochemical state (PS*, a measure of the atmosphere’s
emissions-independent reactivity described in detail by Henneman et al. [4]) in the
80th percentile were included in the regressions. Fits were assessed using a flexible
spline model to capture increasing OPEs at lower NO Z concentrations.