Publication

Heat-wave is one of key meteorological conditions causing the National Ambient Air Quality Standard (NAAQS) exceedance event in urban environment. In this study, the Weather Research and Forecasting model coupled with Chemistry (WRF/Chem) was used to investigate an unusual heat-wave driven ozone (O-3) exceedance event occurring on May 17-19, 2017 in New York City (NYC) and surrounding areas. The WRF/Chem simulations were conducted over the three nested domains with the finest grid spacing of 1.3 km. The simulations were evaluated with various observational data including in situ measurements of air quality and meteorological variables as well as the Lidar-measured vertical profiles. Overall, the WRF/Chem successfully captured the diurnal variations of air quality (e.g., O-3 and nitrogen oxides (NOx)) and meteorological fields during the event. However, the O(3 )was under-predicted during the daytime peak hours but over-predicted during the nighttime. The under-predictions of O-3 were highly associated with over-estimation of the planetary-boundary-layer (PBL) heights and uncertainties of emissions (e.g., NOx, and volatile organic compounds, VOCs), whereas the over-predictions were likely attributed to underestimation of the PBL heights and strong vertical mixing. Several findings are obtained from this study. First, the PBL growth plays a critical role in the development of O-3 episode. The maximum PBLH and the largest PBL growth rates on a high O-3 day are higher than those on a low O-3 day. A strong low-level jet (LLJ) in the lower atmospheric boundary layer with increasing boundary-layer height was observed during the event. Second, the isoprene emissions calculated by the biogenic emission model are underestimated significantly in the WRF/Chem model, which leads to the underprediction of daily O-3 peak values. Third, the process analysis indicates that the local chemical productions are the dominant contributor with the contributions of 63-68% during the ozone-exceedance event.