Influence of lateral and top boundary conditions on regional air quality prediction: A multiscale study coupling regional and global chemical transport models

Abstract

[1] The sensitivity of regional air quality model to various lateral and top boundary conditions is studied at 2 scales: a 60 km domain covering the whole USA and a 12 km domain over northeastern USA. Three global models (MOZART-NCAR, MOZART-GFDL and RAQMS) are used to drive the STEM-2K3 regional model with time-varied lateral and top boundary conditions (BCs). The regional simulations with different global BCs are examined using ICARTT aircraft measurements performed in the summer of 2004, and the simulations are shown to be sensitive to the boundary conditions from the global models, especially for relatively long-lived species, like CO and O 3 . Differences in the mean CO concentrations from three different global-model boundary conditions are as large as 40 ppbv, and the effects of the BCs on CO are shown to be important throughout the troposphere, even near surface. Top boundary conditions show strong effect on O 3 predictions above 4 km. Over certain model grids, the model's sensitivity to BCs is found to depend not only on the distance from the domain's top and lateral boundaries, downwind/upwind situation, but also on regional emissions and species properties. The near-surface prediction over polluted area is usually not as sensitive to the variation of BCs, but to the magnitude of their background concentrations. We also test the sensitivity of model to temporal and spatial variations of the BCs by comparing the simulations with time-varied BCs to the corresponding simulations with time-mean and profile BCs. Removing the time variation of BCs leads to a significant bias on the variation prediction and sometime causes the bias in predicted mean values. The effect of model resolution on the BC sensitivity is also studied. Citation: Tang, Y., et al. (2007), Influence of lateral and top boundary conditions on regional air quality prediction: A multiscale study coupling regional and global chemical transport models,

Decadal regional air quality simulations over Europe in present climate: near surface ozone sensitivity to external meteorological forcing

“…The assumption of constant top boundaries implies that important processes such as stratosphere-troposphere exchange and intercontinental transport of pollutants are not taken into consideration. According to Tang et al (2007) top boundary conditions show strong effect on O 3 predictions above 4 km. From global studies (Stevenson et al, 2006) it is known that stratospheric flux to the troposphere is an important contribution to the global ozone budget and that in future projections upper tropospheric ozone will rise, especially in the Northern Hemisphere, which is related to an increased influx from the stratosphere.…”

Online coupled regional meteorology chemistry models in Europe: current status and prospects

“…Flemming et al, 2009), prescribed fields describing clean or polluted background atmospheres (e.g. climatological averages, see also Tang et al, 2007), or either of those methods modified with increments from a chemical data assimilation system (Elbern and Schmidt, 2001). In offline models the improvement of the initial pollutant fields brings only a limited improvement in the forecast, because the forcing from meteorology and emissions makes the model quickly converge from any reasonable initial condition to a stable solution.…”

Localized Ensemble Kalman Dynamic Data Assimilation for Atmospheric Chemistry

“…The observations used for data assimilation are the ground-level ozone (O 3 ) measurements taken during the ICARTT [9,17] campaign in 2004 (which also includes the initial concentrations, meteorological fields, boundary values, and emission rates). Figure 1.a shows the location of the ground stations (340 in total) that measured ozone concentrations and an ozonesonde (not used in the assimilation process).…”