Effects of the sea-land breeze on coastal ozone pollution in the Yangtze River Delta, China

Aim at the effects of the coastal characteristic on ozone pollution in the Yangtze River Delta (YRD), a campaign was launched at the Ningbo, China in the summer of 2020, which mainly covered the monitoring of the vertical profiles of ozone (O₃) concentration, three-dimensional wind field, temperature and humidity profiles and parameters of boundary layer dynamic-thermodynamic structure. At the coastal research station, a sea-land breeze (SLB) circulation accompanied by a concurrent coastal low-level jets (CLLJ) structure was observed and identified during 11-12 May 2020. The sea breeze first formed at 10:00 LT on 11 May, turned to land breeze at night, and returned to sea breeze again at 10:00 LT the next morning, prevailing at altitudes of 0-0.5 km and 0-0.3 km respectively. Land breeze at night carries O₃ from the inland to the sea forming high ozone levels over the sea, and the shift of the sea breeze during daytime further blew pollution back to the land. Additionally, the conversion of SLB contributed to the occurrence of CLLJ at the altitudes of ~0.3-0.7 km by 02:00 and 06:00 LT, of which the center of wind speed reached ~13 m s^-1. The CLLJ-induced turbulent activity decoupled the residual layer (RL) and stable boundary layer, leading to a reduction of RL-O₃ levels and an increase of ~50 μg m^-3 in surface-O₃ concentration. The YRD's unique coastal characteristics make O₃ pollution causes in coastal areas more complicated.

Ozone and Nitrogen Dioxide Pollution in a Coastal Urban Environment: The Role of Sea Breezes, and Implications of Their Representation for Remote Sensing of Local Air Quality

We present an analysis of sea breeze conditions for the Boston region and examine their impact on the concentration of local air pollutants over the past decade. Sea breezes occur about one-third of the days during the summer and play an important role in the spatial distribution and temporal evolution of NO₂ and O₃ across the urban area. Mornings preceding a sea breeze are characterized by low horizontal wind speeds, low background O₃, and an accumulation of local primary emissions. Air pollution is recirculated inland during sea breezes, frequently coinciding with the highest O₃ measured at the urban center. We use "Ox" (= NO₂ + O₃) to account for temporary O₃ suppression by NO and find large horizontal gradients (differences in Ox greater than 30 ppb across less than 15 km), which are not observed on otherwise westerly or easterly prevailing days. This implies a challenge in surface monitoring networks to adequately represent the spatial variability of secondary air pollution in coastal urban areas. We investigate satellite-based climatologies of tropospheric NO₂, and find evidence of selection biases due to cloud conditions, but show that sea breeze days are well observed due to the fair weather conditions generally associated with these events. The fine scale of the sea breeze in Boston is not reliably represented by meteorological reanalyses products commonly used in chemical transport models required to provide inputs for the satellite-based retrievals. This implies a higher systematic error in the operational retrievals on sea breeze days compared to other days.

The Impact of Iodide-Mediated Ozone Deposition and Halogen Chemistry on Surface Ozone Concentrations Across the Continental United States

The air quality of many large coastal areas in the United States is affected by the confluence of polluted urban and relatively clean marine airmasses, each with distinct atmospheric chemistry. In this context, the role of iodide-mediated ozone (O3) deposition over seawater and marine halogen chemistry accounted for in both the lateral boundary conditions and coastal waters surrounding the continental U.S. is examined using the Community Multiscale Air Quality (CMAQ) model. Several nested simulations are conducted in which these halogen processes are implemented separately in the continental U.S. and hemispheric CMAQ domains, the latter providing lateral boundary conditions for the former. Overall, it is the combination of these processes within both the continental U.S. domain and from lateral boundary conditions that lead to the largest reductions in modeled surface O3 concentrations. Predicted reductions in surface O3 concentrations occur mainly along the coast where CMAQ typically has large overpredictions. These results suggest that a realistic representation of halogen processes in marine regions can improve model prediction of O3 concentrations near the coast.

Regional and Hemispheric Influences on Temporal Variability in Baseline Carbon Monoxide and Ozone over the Northeast US

Interannual variability in baseline carbon monoxide (CO) and ozone (O3), defined as mixing ratios under minimal influence of recent and local emissions, was studied for seven rural sites in the Northeast US over 2001 - 2010. Annual baseline CO exhibited statistically significant decreasing trends (-4.3 - -2.3 ppbv yr-1), while baseline O3 did not display trends at any site. In examining the data by season, wintertime and springtime baseline CO at the two highest sites (1.5 km and 2 km asl) did not experience significant trends. Decadal increasing trends (~2.55 ppbv yr-1) were found in springtime and wintertime baseline O3 in southern New Hampshire, which was associated with anthropogenic NOx emission reductions from the urban corridor. Biomass burning emissions impacted summertime baseline CO with ~38% variability from wildfire emissions in Russia and ~22% from Canada at five sites and impacted baseline O3 at the two high elevation sites only with ~27% variability from wildfires in both Russia and Canada. The Arctic Oscillation was negatively correlated with summertime baseline O3, while the North Atlantic Oscillation was positively correlated with springtime baseline O3. This study suggested that anthropogenic and biomass burning emissions, and meteorological conditions were important factors working together to determine baseline O3 and CO in the Northeast U.S. during the 2000s.

Air pollution, weather, and respiratory emergency room visits in two northern New England cities: an ecological time-series study

Daily emergency room (ER) visits for all respiratory (ICD-9 460-519) and asthma (ICD-9 493) were compared with daily sulfur dioxide (SO2), ozone (O3), and weather variables over the period 1998-2000 in Portland, Maine (population 248,000), and 1996-2000 in Manchester, New Hampshire (population 176,000). Seasonal variability was removed from all variables using nonparametric smoothed function (LOESS) of day of study. Generalized additive models were used to estimate the effect of elevated levels of pollutants on ER visits. Relative risks of pollutants are reported over their interquartile range (IQR, the 75th -25th percentile pollutant values). In Portland, an IQR increase in SO2 was associated with a 5% (95% CI 2-7%) increase in all respiratory ER visits and a 6% (95% CI 1-12%) increase in asthma visits. An IQR increase in O3 was associated with a 5% (95% CI 1-10%) increase in Portland asthmatic ER visits. No significant associations were found in Manchester, New Hampshire, possibly due to statistical limitations of analyzing a smaller population. The absence of statistical evidence for a relationship should not be used as evidence of no relationship. This analysis reveals that, on a daily basis, elevated SO2 and O3 have a significant impact on public health in Portland, Maine.