Contributions of foreign, domestic and natural emissions to US ozone estimated using the path-integral method in CAMx nested within GEOS-Chem

Abstract

Abstract. The Goddard Earth Observing System global chemical transport (GEOS-Chem) model was used at 2 • × 2.5 • resolution to simulate ozone formation for a base case representing year 2010 and a natural background case without worldwide anthropogenic emissions. These simulations provided boundary concentrations for base and natural background simulations with the Comprehensive Air Quality Model with Extensions (CAMx) on a North American domain (one-way nested) at 12 km × 12 km resolution over March-September 2010. The predicted maximum daily average 8 h (MDA8) background ozone for the US is largest in the mountainous areas of Colorado, New Mexico, Arizona, and California. The background MDA8 ozone in some of these locations exceeds 60 ppb, when averaged over the 10 days with the largest base-case ozone (T10base average). The background ozone generally becomes both a larger fraction of the base-case ozone in the western US and a smaller fraction in the eastern US when proceeding from spring to summer to the T10base average. The ozone difference between the base and background cases represents the increment to ozone from all anthropogenic sources. The path-integral method was applied to allocate this anthropogenic ozone increment to US anthropogenic emissions, Canadian/Mexican anthropogenic emissions, and the anthropogenic components of the lateral and top boundary concentrations (BCs). Using the T10base average MDA8 ozone, the relative importance of the sources is generally US emissions > anthropogenic lateral BCs > Canadian/Mexican emissions anthropogenic top BCs. Specifically, for 10 US urban areas, the source contributions were 12-53 ppb for US emissions, 3-9 ppb for lateral BCs, 0.2-3 ppb for Canadian/Mexican emissions, and ≤ 0.1 ppb for top BCs. The contributions of the lateral BCs are largest for the higherelevation US sites in the Intermountain West and along the western boundary of the domain. In Denver, for example, the lateral BCs contribute 44 % to the T10base anthropogenic increment. Averaging over the 10 days in the background case with the largest MDA8 ozone (T10bkgd), the contribution from US emissions is reduced to 3-13 ppb at the 10 urban sites, leading to a reduction in the anthropogenic ozone increment. The contribution of the Canadian/Mexican emissions remains about the same (0.3-2 ppb), and the contribution from the lateral BCs increases (5-10 ppb), especially at the lower-elevation urban sites. The net effect at the urban sites is that the relative importance of the anthropogenic lateral BCs is significantly greater for the T10bkgd average than the T10base average. This is also true for rural sites studied, where the anthropogenic lateral BC contribution becomes as large as 68 % of the anthropogenic increment for the T10bkgd average. In addition to the source apportionment, we also used surface and ozonesonde measurements to evaluate GEOS-Chem and CAMx performance.

Implementation of Yale Interactive terrestrial Biosphere model v1.0 into GEOS-Chem v12.0.0: a tool for biosphere–chemistry interactions

“…YIBs is a terrestrial vegetation model designed to simulate the land carbon cycle with dynamical prediction of LAI and tree height (Yue and Unger, 2015). The YIBs model applies the Farquhar et al (1980) scheme to calculate leaf level photosynthesis, which is further upscaled to the canopy level by the separation of sunlit and shaded leaves (Spitters, 1986). The canopy is divided into an adaptive number of layers (typically 2-16) for light stratification.…”

“…For different PFTs, appropriate photosynthetic parameters are derived from the Community Land Model (CLM; Bonan et al, 2011). The net leaf photosynthesis for C 3 and C 4 plants is computed based on well-established Michaelis-Menten enzymekinetics scheme (Farquhar et al, 1980;von Caemmerer and Farquhar, 1981):…”

“…php/GEOS-Chem_12#12.0.0, last access: 10 January 2020). The GEOS-Chem (GC) model has been widely used in episode prediction (Cui et al, 2016), source attribution (D'Andrea et al, 2016;Dunker et al, 2017;Ni et al, 2018;Lu et al, 2019), future pollution projection Ramnarine et al, 2019), health risk assessment (Xie et al, 2019), and so on. The standard GC model uses prescribed vegetation parameters and as a result cannot depict the changes in chemical components due to biosphere-pollution interactions.…”

Attributing differences in the fate of lateral boundary ozone in AQMEII3 models to physical process representations

“…However, since these sensitivity simulations were not part of the original design for AQMEII3 and entail additional nontrivial resource commitments from each participating organization, most sensitivity simulations are not available except for WRF/DEHM_noddry (Table 2). In addition, the vertical resolution, especially in the free troposphere, has been shown to be important for air quality models (e.g., Mathur et al, 2017;Eastham and Jacob, 2017). To investigate the impact of this physical treatment on LB ozone, a sensitivity simulation WRF/CMAQ_27aL was conducted.…”

“…The contribution of ozone from outside the US to the surface ozone within the US has been estimated by several studies with different approaches, including source sensitivity approaches (such as the "brute force" method; e.g., , the path-integral method (Dunker et al, 2017), and tagged species approaches such as the integrated source apportionment method (ISAM) for CMAQ (Kwok et al, 2015), ozone source apportionment technology (OSAT) for CAMx (Ramboll, 2018), and chemically reactive tracers Nopmongcol et al, 2017).…”