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Simulation of summertime U.S. surface ozone diurnal cycle is influenced by the model representation of planetary boundary layer (PBL) mixing, spatial resolution, and precursor emissions. These factors are investigated here for five major regions (Northeast, Midwest, Southeast, California, and Southwest) by using the Model for Ozone And Related chemical Tracers version 2.4 (MOZART-2.4), with important modifications, to conduct sensitivity experiments for summer 1999 with three PBL mixing schemes, two horizontal resolutions and two emissions datasets. Among these factors, the PBL mixing is dominant. The default non-local scheme well reproduces the observed ozone diurnal variation, where the timing for the afternoon maximum and the morning minimum is within 1h of the observed; biases for the minimum are less than 5ppb except over the Southeast; and the ozone maximum–minimum contrast (OMMC) is within 10ppb of observations except for the overprediction by 18.9ppb over the Northeast. In contrast, the local scheme significantly overestimates the OMMC by 10–34ppb over all regions as ozone and precursors are trapped too close to the ground. On the other hand, the full-mixing assumption underestimates the OMMC by 0–25ppb, except over the Northeast, as the nighttime ozone decline is greatly underpredicted. As compared to PBL mixing, the effects of horizontal resolutions and precursor emissions being used are smaller but non-negligible. Overall, with the non-local mixing scheme, relatively high horizontal resolution (∼1.1°) and updated emissions data, the modified MOZART is capable of simulating the main features of the observed ozone diurnal cycle. [Copyright &y& Elsevier]

In this study, we investigated the daily variability of PM 10 concentrations in January in Korea during the past 19 years (2001-2019), as well as the associated atmospheric circulation patterns. The daily PM 10 concentrations were classified into three cases: low (L; < 50 μg/m 3 ), high (H; 50-100 μg/m 3 ), and extremely high (EH; ≥ 100 μg/m 3 ). We found that the strength of the East Asian winter monsoon influenced the PM 10 variability in the L and H cases. However, the EH cases were strongly influenced by the rapid growth of barotropic warming (anticyclonic anomaly) over the eastern North Atlantic and Northern Europe (ENE), and the stationary Rossby waves grew rapidly over Eurasia within only four days. Analysis of the quasi-geostrophic geopotential tendency budget revealed that the anticyclonic anomaly over the ENE was enhanced by vorticity advection. Linear baroclinic model experiments confirmed that vorticity forcing over the ENE induces favorable atmospheric conditions for the occurrence of EH PM 10 events in East Asia. As a result, the PM 10 concentration sharply increased sharply by approximately three times over four days. This study suggests that understanding atmospheric teleconnections between the ENE and East Asia can effectively predict the occurrence of EH PM 10 events in Korea, helping to reduce the human health risks from atmospheric pollution., (Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved.)