Air Pollutant Concentrations and Trends over the Eastern U.S. and China: Aircraft Measurements and Numerical Simulations

In the last several decades, efforts have been made to mitigate air pollution all around the world. With surface observations showing substantial decrease of criteria pollutants, including O3, NOx, CO and SO2, the long-term aircraft measurements over the eastern U.S. provide a unique opportunity to study the trend of the air pollutant column contents and the regional transport in the free troposphere. Analyses of the historical data indicated ~2.0 Dobson Unit/decade decrease in tropospheric O3 columns over the eastern U.S. with a similar decreasing trend of CO. The statistical analysis also showed a significant decreasing trend for tropospheric SO2. Analyses of the EPA CEMS emission data showed parallel reductions. A case study of tropospheric O3 and SO2 over downwind area of Baltimore showed that the regional transport by westerly wind from Ohio and Pennsylvania play an important role in the local air quality issues. As the second largest economy in the world, China's rapid economic growth in the last decade lead to a dramatic increase in energy demand, which relied heavily on coal burning. The enormous amount of SO2 emissions caused severe environmental issues including acid deposition and particulate matter pollution. To mitigate these air quality problems, strict control measures and regulations were applied to abate sulfur emissions, especially before and during the 2008 Beijing Olympics. Aircraft measurements of tropospheric SO2 were conducted over central China in spring 2008, where intense measurements are lacking. A substantial amount of SO2 was observed in the free troposphere, which is important to regional transport and remote sensing. I successfully validated the SO2 columns with satellite retrievals, and proved that the new OMI SO2 algorithm performs better than the conventional algorithm. An emission inventory was evaluated through a combination of model simulations and satellite products. Between 2006 and 2008, the SO2 emissions had been reduced substantially over middle and eastern China. I also analyzed the model simulations, and find the SO2 lifetime is ~ 38 h during spring in China and that ~50% of Chinese emissions are exported to the western Pacific

Predicting fine-scale daily NO2 over Mexico city using an ensemble modeling approach

In recent years, there has been growing interest in developing air pollution prediction models to reduce exposure measurement error in epidemiologic studies. However, efforts for localized, fine-scale prediction models have been predominantly focused in the United States and Europe. Furthermore, the availability of new satellite instruments such as the TROPOsopheric Monitoring Instrument (TROPOMI) provides novel opportunities for modeling efforts. We estimated daily ground-level nitrogen dioxide (NO2) concentrations in the Mexico City Metropolitan Area at 1-km2 grids from 2005 to 2019 using a four-stage approach. In stage 1 (imputation stage), we imputed missing satellite NO2 column measurements from the Ozone Monitoring Instrument (OMI) and TROPOMI using the random forest (RF) approach. In stage 2 (calibration stage), we calibrated the association of column NO2 to ground-level NO2 using ground monitors and meteorological features using RF and extreme gradient boosting (XGBoost) models. In stage 3 (prediction stage), we predicted the stage 2 model over each 1-km2 grid in our study area, then ensembled the results using a generalized additive model (GAM). In stage 4 (residual stage), we used XGBoost to model the local component at the 200-m2 scale. The cross-validated R2 of the RF and XGBoost models in stage 2 were 0.75 and 0.86 respectively, and 0.87 for the ensembled GAM. Cross-validated root-mean-squared error (RMSE) of the GAM was 3.95 μg/m3. Using novel approaches and newly available remote sensing data, our multi-stage model presented high cross-validated fits and reconstructs fine-scale NO2 estimates for further epidemiologic studies in Mexico City

Analysis of NO2 and O3 Total Columns from DOAS Zenith-Sky Measurements in South Italy

The Gas Absorption Spectrometer Correlating Optical Difference—New Generation 4 (GASCOD/NG4) is a multi-axis differential optical absorption spectroscopy (MAX-DOAS) instrument which measures diffuse solar spectra at the Environmental-Climate Observatory (ECO) of the Italian research institute CNR-ISAC, near Lecce. The high-resolution spectra measured in zenith-sky configuration were used to retrieve the NO2 and O3 vertical column densities (VCDs) from March 2017 to November 2019. These good-quality data, proven by the comparison with the Ozone Monitoring Instrument (OMI) and TROPOspheric Monitoring Instrument (TROPOMI) satellite measurements, were used to characterize the ECO site by exploiting the sinergy with in situ NO2 and O3 concentrations and meteorological data. Although stratospheric processes seem to be the main forces behind the NO2 and O3 VCDs seasonal trends, diurnal variabilities revealed the presence of a tropospheric signal in the NO2 VCDs, which had significant lower values during Sundays. Comparison with wind data acquired at the ECO observatory, at 20 m above the ground, revealed how NO2 VCDs are influenced by both tropospheric local production and transport from the nearby city of Lecce. On the other hand, no significant tropospheric signal was contained in the O3 VCDs

An acoustic view of ocean mixing

Knowledge of the parameter K (turbulent diffusivity/"mixing intensity") is a key to understand transport processes of matter and energy in the ocean. Especially the almost vertical component of K across the ocean stratification (diapycnal diffusivity) is vital for research on biogeochemical cycles or greenhouse gas budgets. Recent boost in precision of water velocity data that can be obtained from vessel-mounted acoustic instruments (vmADCP) allows identifying ocean regions of elevated diapycnal diffusivity during research cruises - in high horizontal resolution and without extra ship time needed. This contribution relates acoustic data from two cruises in the Tropical North East Atlantic Oxygen Minimum Zone to simultaneous field observations of diapycnal diffusivity: pointwise measurements by a microstructure profiler as well as one integrative value from a large scale Tracer Release Experiment

Atmospheric effects of the emerging mainland Chinese transportation system at and beyond the regional scale

Local surface travel needs in the People's Republic of China (mainland China) have traditionally been met largely by nonpolluting bicycles. A major automobile manufacturing/importing effort has begun in the country over the last decade, and planning documents indicate that the Chinese may strive to acquire more than 100 million vehicles early in the next century. By analogy with large automotive fleets already existing in the western world, both regional and global scale pollution effects are to be expected from the increase. The present work adopts the latest projections of Chinese automobile manufacture and performs some quantitative assessments of the extent of pollution generation. Focus for the investigation is placed upon the oxidant ozone. Emissions of the precursor species nitrogen oxides and volatile organics are constructed based on data for the current automotive sector in the eastern portion of the United States. Ozone production is first estimated from measured values for continental/oceanic scale yields relative to precursor oxidation. The estimates are then corroborated through idealized two dimensional modeling of the photochemistry taking place in springtime air flow off the Asian land mass and toward the Pacific Ocean. The projected fleet sizes could increase coastal and remote oceanic ozone concentrations by tens of parts per billion (ppb) in the lower troposphere. Influences on the tropospheric aerosol system and on the major greenhouse gas carbon dioxide are treated peripherally. Nitrogen oxides created during the vehicular internal combustion process will contribute to nitrate pollution levels measured in the open Pacific. The potential for soot and fugitive dust increases should be considered as the automotive infrastructure develops. Since the emerging Chinese automotive transportation system will represent a substantial addition to the global fleet and all the carbon in gasoline is eventually oxidized completely, a significant rise in global carbon dioxide inputs will ensue as well. Some policy issues are treated preliminary. The assumption is made that alterations to regional oxidant/aerosol systems and to terrestrial climate are conceivable. The likelihood that the Chinese can achieve the latest vehicle fleet goals is discussed, from the points of view of new production, positive pollution feedbacks from a growing automobile industry, and known petroleum reserves. Vehicular fuel and maintenance options lying before the Chinese are outlines and compared. To provide some perspective on the magnitude of the environmental changes associated with an Asian automotive buildup, recent estimates of the effects of future air traffic over the Pacific Rim are described

Temporal Variation of NO2 and O3 in Rome (Italy) from Pandora and In Situ Measurements

To assess the best measures for the improvement of air quality, it is crucial to investigate in situ and columnar pollution levels. In this study, ground-based measurements of nitrogen dioxide (NO2) and ozone (O-3) collected in Rome (Italy) between 2017 and 2022 are analyzed. Pandora sun-spectrometers provided the time series of the NO2 vertical column density (VC-NO2), tropospheric column density (TC-NO2), near-surface concentration (SC-NO2), and the O-3 vertical column density (VC-O-3). In situ concentrations of NO2 and O-3 are provided by an urban background air quality station. The results show a clear reduction of NO2 over the years, thanks to the recent ecological transition policies, with marked seasonal variability, observable both by columnar and in situ data. Otherwise, O-3 does not show inter-annual variations, although a clear seasonal cycle is detectable. The results suggest that the variation of in situ O-3 is mainly imputable to photochemical reactions while, in the VC-O-3, it is triggered by the predominant contribution of stratospheric O-3. The outcomes highlight the importance of co-located in situ and columnar measurements in urban environments to investigate physical and chemical processes driving air pollution and to design tailored climate change adaptation strategies

Comparison between economic growth and satellite-based measurements of NO2 pollution over northern Italy

The aim of this study is to investigate to what extent spatiotemporal fluctuations in the tropospheric NO2 column concentration can map variations in economic output. To do so satellite based tropospheric NO2 column measurements obtained from the ERS-2, ENVISAT, MetOp-A, and MetOp-B satellite missions covering the period from 1996 to 2017 over the Po valley in northern Italy is analyzed. A harmonic analysis is carried out in order to exclude influences such as the annual or semi-annual cycle. Afterwards the residues of the tropospheric NO2 time series are further investigated by means of a wavelet analysis method. The result is a spectrogram which implies the NO2 variability for the study area between 1996 and 2017. Therefore, the gross domestic product (GDP) is used as an indicator for economic performance and thus, as an approximation, of anthropogenically induced NO2 pollution. Clear conspicuous signatures occurred almost simultaneously both within the temporal development of the GDP growth rate and the spectral characteristic of the NO2 variability during the studied period. The comparison of the temporal course of the GDP shows that the period of systematically reduced spectral intensity in NO2 coincides strikingly well with the period of the global financial crisis in 2008 which was then followed by a second crisis in 2014. The economic growth decreased by 7.9% between 2007 and 2009 and by 5.2% between 2011 and 2014 in comparison to the same quarter of the previous year. It is found that during the crises (2007–2013) the variability of NO2 is reduced by about 80%

Assessment of variations in air quality in cities of Ecuador in relation to the lockdown due to the COVID-19 pandemic

This study analyzes the effect of lockdown due to COVID-19 on the spatiotemporal variability of ozone (O3), sulfur dioxide (SO2), and nitrogen dioxide (NO2) concentrations in different provinces of continental Ecuador using satellite information from Sentinel - 5P. The statistical analysis includes data from 2018 to March 2021 and was performed based on three periods defined a priori: before, during, and after lockdown due to COVID-19, focusing on the provinces with the highest concentrations of the studied gases (hotspots). The results showed a significant decrease in NO2 concentrations during the COVID-19 lockdown period in all the study areas: the Metropolitan District of Quito (DMQ) and the provinces of Guayas and Santo Domingo de los Ts & PRIME;achilas. In the period after lockdown, NO2 concentrations increased by over 20% when compared to the pre-lockdown period, which may be attributable to a shift towards private transportation due to health concerns. On the other hand, SO2 concentrations during the lockdown period showed irregular, non-significant variations; however, increases were observed in the provinces of Chimborazo, Guayas, Santa Elena, and Morona Santiago, which could be partly attributed to the eruptive activity of the Sangay volcano during 2019-2020. Conversely, O3 concentrations increased by 2-3% in the study areas; this anomalous behavior could be attributed to decreased levels of NOx, which react with ozone, reducing its concentration. Finally, satellite data validation using the corresponding data from monitoring stations in the DMQ showed correlation values of 0.9 for O3 data and 0.7 for NO2 data, while no significant correlation was found for SO2.info:eu-repo/semantics/publishedVersio

Europe-wide air pollution modeling from 2000 to 2019 using geographically weighted regression

Previous European land-use regression (LUR) models assumed fixed linear relationships between air pollution concentrations and predictors such as traffic and land use. We evaluated whether including spatially-varying relationships could improve European LUR models by using geographically weighted regression (GWR) and random forest (RF). We built separate LUR models for each year from 2000 to 2019 for NO2, O3, PM2.5 and PM10 using annual average monitoring observations across Europe. Potential predictors included satellite retrievals, chemical transport model estimates and land-use variables. Supervised linear regression (SLR) was used to select predictors, and then GWR estimated the potentially spatially-varying coefficients. We developed multi-year models using geographically and temporally weighted regression (GTWR). Five-fold cross-validation per year showed that GWR and GTWR explained similar spatial variations in annual average concentrations (average R(2) = NO2: 0.66; O3: 0.58; PM10: 0.62; PM2.5: 0.77), which are better than SLR (average R(2) = NO2: 0.61; O3: 0.46; PM10: 0.51; PM2.5: 0.75) and RF (average R(2) = NO2: 0.64; O3: 0.53; PM10: 0.56; PM2.5: 0.67). The GTWR predictions and a previously-used method of back-extrapolating 2010 model predictions using CTM were overall highly correlated (R(2) > 0.8) for all pollutants. Including spatially-varying relationships using GWR modestly improved European air pollution annual LUR models, allowing time-varying exposure-health risk models