Intercontinental transport of pollution manifested in the variability and seasonal trend of springtime O3 at northern middle and high latitudes

Observations (0–8 km) from the Tropospheric Ozone Production about the Spring Equinox (TOPSE) experiment are analyzed to examine air masses contributing to the observed variability of springtime O3 and its seasonal increase at 40°–85°N over North America. Factor analysis using the positive matrix factorization and principal component analysis methods is applied to the data set with 14 chemical tracers (O3, NOy, PAN, CO, CH4, C2H2, C3H8, CH3Cl, CH3Br, C2Cl4, CFC-11, HCFC-141B, Halon-1211, and 7Be) and one dynamic tracer (potential temperature). Our analysis results are biased by the measurements at 5–8 km (70% of the data) due to the availability of 7Be measurements. The identified tracer characteristics for seven factors are generally consistent with the geographical origins derived from their 10 day back trajectories. Stratospherically influenced air accounts for 14 ppbv (35–40%) of the observed O3 variability for data with O3concentrations \u3c100 ppbv at middle and high latitudes. It accounts for about 2.5 ppbv/month (40%) of the seasonal O3 trend at midlatitudes but for only 0.8 ppbv/month (\u3c20%) at high latitudes, likely reflecting more vigorous midlatitude dynamical systems in spring. At midlatitudes, reactive nitrogen-rich air masses transported through Asia are much more significant (11 ppbv in variability and 3.5 ppbv/month in trend) than other tropospheric contributors. At high latitudes the O3 variability is significantly influenced by air masses transported from lower latitudes (11 ppbv), which are poor in reactive nitrogen. The O3 trend, in contrast, is largely defined by air masses rich in reactive nitrogen transported through Asia and Europe across the Pacific or the Arctic (3 ppbv/month). The influence from the stratospheric source is more apparent at 6–8 km, while the effect of O3 production and transport within the troposphere is more apparent at lower altitudes. The overall effect of tropospheric photochemical production, through long-range transport, on the observed O3 variability and its seasonal trend is more important at high latitudes relative to more photochemically active midlatitudes

Validation of Aura Microwave Limb Sounder OH measurements with Fourier Transform Ultra-Violet Spectrometer total OH column measurements at Table Mountain, California

The first seasonal and interannual validation of OH measurements from the Aura Microwave Limb Sounder (MLS) has been conducted using ground-based OH column measurements from the Fourier Transform Ultra-Violet Spectrometer (FTUVS) over the Jet Propulsion Laboratory's Table Mountain Facility (TMF) during 2004–2007. To compare with FTUVS total column measurements, MLS OH vertical profiles over TMF are integrated to obtain partial OH columns above 21.5 hPa, which covers nearly 90% of the total column. The tropospheric OH and the lower stratopheric OH not measured by MLS are estimated using GEOS (Goddard Earth Observing System)-Chem and a Harvard 2-D model implemented within GEOS-Chem, respectively. A number of field observations and calculations from a photochemical box model are compared to OH profiles from these models to estimate the variability in the lower atmospheric OH and thus the uncertainty in the combined total OH columns from MLS and models. In general, the combined total OH columns agree extremely well with TMF total OH columns, especially during seasons with high OH. In winter with low OH, the combined columns are often higher than TMF measurements. A slightly weaker seasonal variation is observed by MLS relative to TMF. OH columns from TMF and the combined total columns from MLS and models are highly correlated, resulting in a mean slope of 0.969 with a statistically insignificant intercept. This study therefore suggests that column abundances derived from MLS vertical profiles have been validated to within the mutual systematic uncertainties of the MLS and FTUVS measurements

Constraining global biogenic emissions and exploring source contributions to tropospheric ozone: modeling applications.

Biogenic isoprene plays an important role in tropospheric chemistry. We use HCHO column measurements by the Global Ozone Monitoring Experiment (GOME) to constrain isoprene emissions. Using the global Goddrad Earth Observing SystemChemistry (GEOS-Chem) as the forward model, a Bayesian inversion of GOME HCHO observations from September 1996 to August 1997 is conducted. Column contributions to HCHO from 12 sources including 10 terrestrial ecosystem groups, biomass burning, and industry are considered and inverted for 8 geographical regions globally. The a posteriori solution reduces the model biases for all regions, and estimates the annual global isoprene emissions of 566 Tg C yr-1, ~50% larger than the a priori estimate. Compared to the Global Emissions Inventory Activity (GEIA) inventory (~500 Tg C yr-1), the a posteriori isoprene emissions are generally higher at mid latitudes and lower in the tropics. This increase of global isoprene emissions significantly affects tropospheric chemistry, decreasing the global mean OH concentration by 10.8% to 0.95106 molecules/cm3. The atmospheric lifetime of CH3CCl3 increases from 5.2 to 5.7 years. Positive matrix factorization (PMF), an advanced method for source apportionment, is applied to TRAnsport of Chemical Evolution over the Pacific (TRACE-P) measurements and it is found that cyanogenesis in plants over Asia is likely an important emission process for CH3COCH3 and HCN. This approach also is applied to estimate source contributions to the tropospheric ozone (O3) with Tropospheric Ozone Production about the Spring Equinox (TOPSE) and TRACE-P measurements. The corresponding GEOS-Chem simulations are applied to the same factor-projected space in order to evaluate the model simulations. Intercontinental transport of pollutants is most responsible for increasing trend of springtime O3, while stratospheric influence is the largest contributions to troposperic O3 variability at northern middle and high latitudes. On the other hand, the overall tropospheric contributions to O3 variability are more important at northern low latitudes by long-range transport, biomass burning, and industry/urban emissions. In general, the simulated O3 variabilities are comparable with those of observations. However, the model underestimates the trends of and the contributions to O3 variability by long-range transport of O3 and its precursors at northern middle and high latitudes.Ph.D.Committee Chair: Wang Yuhang; Committee Member: Cunnold Derek; Committee Member: Guillas Serge; Committee Member: Nenes Athanasios; Committee Member: Weber Rodne

Policy Measures for Mitigating Fine Particle Pollution in Korea and Suggestions for Expediting International Dialogue in East Asia

The majority of the measurements sites over Republic of Korea place PM2.5 concentrations above the national air quality standard of 25 microgram/m3/year, posing great concerns for the national environment and public health. This particulate matter (PM) pollution is often associated with transboundary transport of air pollutants throughout East Asian countries. This paper reviews and discusses the Korean government’s policies for mitigating PM pollution, and in particular, recent policies to control PM2.5, including a system introduced by the Korean Ministry of Environment (KMOE). In addition, I analyze the system and performance of cooperative programs for improving East Asian air quality, considering current approaches by the Acid Deposition Monitoring Network in East Asia (EANET), the Joint Research Project on Long-range Transboundary Air Pollutants in North-East Asia (LTP), the North-East Asian Subregional Programme for Environmental Cooperation (NEASPEC), and Tripartite Environment Minister Meeting (TEMM) as the basis for a comparative study, focusing on international coordination, communication, scientific activities, and institutional structure. Based on this analysis, I have generated some recommendations for improving international dialogue on air quality over East Asia

Impact of a national plan for future electricity supply on ambient air quality in South Korea

AbstractSouth Korea has recently chosen coal as the major energy source for the future national electricity power supply, mainly due to economic reasons. This has raised concerns about national air quality, considering the serious air pollution associated with the long-range transport of Chinese air pollutants. In the present study, we simulated air pollution levels for 2027 considering the changes in electricity power plants of South Korea proposed by the sixth Basic Plan for Long-Term Electricity Supply and Demand (6th BPE, 2013–2027). Compared to the emissions in 2010, the emissions of CO, NOx, SOx, and PM10 from electricity supply in the Incheon, Gyunggi, Gangwon, Chungnam, and Gyeongnam regions will increase by 20–50% in 2027. The resulting number of days on which pollution levels exceeded the national air quality standards for O3 and PM10 will increase by fewer than 6 days in all regions, which seems to be a minor increase. However, that of NO2 over the Seoul metropolitan area (SMA, including Incheon, part of Gyunggi, and Seoul) showed a marked increase of more than 21 days. Therefore, an impact from secondary air pollution, such as acid rain and PM2.5 formation, can be expected, although this requires quantification

Inverse Modeling of the Global Methyl Chloride Sources

Inverse modeling using Bayesian least-squares method is applied to constrain better the sources and sinks of atmospheric methyl chloride (CH3Cl) using the observations from 7 surface stations and 8 aircraft field experiments. We use a 3-D global chemical transport model, the GEOS-CHEM, as the forward model. Up to 39 parameters describing the continental/hemispheric and seasonal dependence of the major sources are used in the inversion. We find that the available surface and aircraft observations cannot constrain all the parameters, resulting in relatively large uncertainties in the inversion results. By examining the degrees of freedom in the inversion Jacobian matrix, we choose a reduced set of parameters that can be constrained by the observations while providing valuable information on the sources and sinks. In particular, we resolve the seasonal dependence of the biogenic and biomass burning sources for each hemisphere. The aircraft in situ measurements are found to provide better constraints on the emission sources than surface measurements. The a posteriori emissions result in better agreement with the observations particularly at southern high latitudes. The a posteriori biogenic and biomass burning source decrease by 13 and 11 % to 2500 and 545 Gg yr-1, respectively, while the a posteriori net ocean source increases by about a factor of 2 to 761 Gg yr-1. The decrease in biomass burning emissions is largely due to the reduction in the emissions in seasons other than spring in the northern hemisphere. The inversion results indicate that the biogenic source has a clear winter minimum in both hemispheres, likely reflecting the decrease of biogenic activity during that season.

Characterization of PM2.5 Mass in Relation to PM1.0 and PM10 in Megacity Seoul

Abstract This study examines the PM2.5 characteristics in Seoul in relation to those of PM1.0 and PM10. Samples were typically collected daily on filters and a few hours sampling were conducted during a few haze events (March 2007 to June 2008). Mean mass concentrations of PM1.0, PM2.5, and PM10 were 19.7 μg/m3, 26.0 μg/m3, and 48.2 μg/m3, respectively, and PM2.5 was reasonably correlated with PM1.0 (γ=0.79) and PM10 (γ=0.52). Three mass group types were mainly distinguished. Group 1 (31%): linear increase of PM1.0 with PM10 and high OC and NO3−; Group 2 (17%): PM10 considerably higher than PM1.0 and high Ca2+ and SO42−; Group 3 (52%): PM1.0 relatively more enhanced than PM10 and highest carbonaceous fraction against mass. The fine mode fraction was lowest (highest) in Group 2 (Group 3). Haze and dust episodes relating to Chinese outflows were mostly evident in Groups 1 and 2, respectively; average PM2.5 concentrations were visibly higher than in Group 3. Non-Negative Matrix Factorization analysis demonstrated that traffic-related urban primary (28%) and coal-fired industry (27%) emissions equally contributed to the PM2.5 mass, followed by aged urban secondary (19%), soil mineral (16%), and biomass combustion (10%) sources. Seasonal variations were apparent in air mass trajectories. Urban primary and coal-fired industry factors were predominant in Group 3 under stagnant conditions in the warm season and under a strong northerly wind in the cold season, respectively. However, contributions of the other three factors were higher in Groups 1 and 2. This study shows that the PM2.5 mass in Seoul is largely dependent on high concentration episodes occurring mostly in cold seasons. It also shows that local emissions contribute considerably during warm months, while the influence of Chinese outflow predominates during cold months

Spatially Refined Aerosol Direct Radiative Forcing Efficiencies

Global aerosol direct radiative forcing (DRF) is an important metric for assessing potential climate impacts of future emissions changes. However, the radiative consequences of emissions perturbations are not readily quantified nor well understood at the level of detail necessary to assess realistic policy options. To address this challenge, here we show how adjoint model sensitivities can be used to provide highly spatially resolved estimates of the DRF from emissions of black carbon (BC), primary organic carbon (OC), sulfur dioxide (SO₂), and ammonia (NH₃), using the example of emissions from each sector and country following multiple Representative Concentration Pathway (RCPs). The radiative forcing efficiencies of many individual emissions are found to differ considerably from regional or sectoral averages for NH₃, SO₂ from the power sector, and BC from domestic, industrial, transportation and biomass burning sources. Consequently, the amount of emissions controls required to attain a specific DRF varies at intracontinental scales by up to a factor of 4. These results thus demonstrate both a need and means for incorporating spatially refined aerosol DRF into analysis of future emissions scenario and design of air quality and climate change mitigation policies