In an environment with many local, remote, persistent, and episodic sources of pollution, meteorology is the primary factor that drives periods of unhealthy air quality and reduced visibility. The 2016 Korea-UnitedStatesAirQuality(KORUS-AQ)fieldstudyprovidesauniqueopportunitytoexaminethe impactofmeteorologyontherelativeinfluenceoflocalandtransboundarypollution.MuchoftheKORUS-AQ campaign can be grouped into four distinct research periods based on observed synoptic meteorology, includingaperiodofcomplexaerosolverticalprofilesdrivenbydynamicmeteorology,stagnationundera persistent anticyclone, low-level transport and haze development, and a blocking pattern. These episodes areexaminedusingadiversearchiveofground,airborne,andsatellitedata.Whilefrontalboundaries are recognized as the primary mechanism driving pollution transport in eastern Asia, results show that they are not always related to sustained periods of hazardous air quality and reduced visibility at the surface.Significantlong-rangetransportofpollutionanddustwasconstrainedtoafewshortevents, suggesting that the majority of pollutants sampled during KORUS-AQ originated from local sources. A severeregionalpollutionepisodeisexaminedindetail,featuringdensehazeandsignificantsecondary particle formation within a shallow moist boundary layer. Observations during KORUS-AQ also highlight a rapid,40ppbvincreaseinozonepollutionasastrongseabreezefronttraversedtheSeoulMetropolitan Area. Representativeness of meteorology and pollution conditions measured by KORUS-AQ is considered by comparison with climatology. This analysis is an essential step toward improved local and regional forecasting of air quality and visibility.

[1] Airborne measurements of CH 2 O were acquired employing tunable diode laser absorption spectroscopy during the 2001 Transport and Chemical Evolution Over the Pacific (TRACE-P) study onboard NASA's DC-8 aircraft. Above $2.5 km, away from the most extreme pollution influences and heavy aerosol loadings, comprehensive comparisons with a steady state box model revealed agreement to within ±37 pptv in the measurement and model medians binned according to altitude and longitude. Likewise, a near unity slope (0.98 ± 0.03) was obtained from a bivariate fit of the measurements, averaged into 25 pptv model bins, versus the modeled concentrations for values up to $450 pptv. Both observations suggest that there are no systematic biases on average between CH 2 O measurements and box model results out to model values $450 pptv. However, the model results progressively underpredict the observations at higher concentrations, possibly due to transport effects unaccounted for in the steady state model approach. The assumption of steady state also appears to contribute to the scatter observed in the point-by-point comparisons. The measurement-model variance was further studied employing horizontal flight legs. For background legs screened using a variety of nonmethane hydrocarbon (NMHC) tracers, measurement and model variance agreed to within 15%. By contrast, measurement variance was $60% to 80% higher than the model variance, even with small to modest elevations in the NMHC tracers. Measurement-model comparisons of CH 2 O in clouds and in the lower marine troposphere in the presence of marine aerosols suggest rather significant CH 2 O uptake by as much as 85% in one extreme case compared to expectations based on modeled gas phase processes.

[1] Aerosol data collected near Asia on the DC-8 aircraft platform during TRACE-P has been examined for evidence of uptake of NO 3 À and SO 4 = on dust surfaces. Data is compared between a sector where dust was predominant and a sector where dust was less of an influence. Coincident with dust were higher mixing ratios of anthropogenic pollutants. HNO 3 , SO 2 , and CO were higher in the dust sector than the nondust sector by factors of 2.7, 6.2, and 1.5, respectively. The colocation of dust and pollution sources allowed for the uptake of NO 3 À and nss-SO 4 = on the coarse dust aerosols, increasing the mixing ratios of these particulates by factors of 5.7 and 2.6 on average. There was sufficient nss-SO 4 = to take up all of the NH 4 + present, with enough excess nss-SO 4 = to also react with dust CaCO 3 . This suggests that the enhanced NO 3 À was not in fine mode NH 4 NO 3 . Particulate NO 3 À (p-NO 3 À ) constituted 54% of the total NO 3 À (t-NO 3 À ) on average, reaching a maximum of 72% in the dust sector. In the nondust sector, p-NO 3 À contributed 37% to t-NO 3 À , likely due to the abundance of sea salts there. In two other sectors where the influence of dust and sea salt were minimal, p-NO 3 À accounted for <15% of t-NO 3 À .

The Geostationary Coastal and Air Pollution Events (GEO-CAPE) mission was recommended by the National Research Council's (NRC's) Earth Science Decadal Survey to measure tropospheric trace gases and aerosols and coastal ocean phytoplankton, water quality, and biogeochemistry from geostationary orbit, providing continuous observations within the field of view. To fulfill the mandate and address the challenge put forth by the NRC, two GEO-CAPE Science Working Groups (SWGs), representing the atmospheric composition and ocean color disciplines, have developed realistic science objectives using input drawn from several community workshops. The GEO-CAPE mission will take advantage of this revolutionary advance in temporal frequency for both of these disciplines. Multiple observations per day are required to explore the physical, chemical, and dynamical processes that determine tropospheric composition and air quality over spatial scales ranging from urban to continental, and over temporal scales ranging from diurnal to seasonal. Likewise, high-frequency satellite observations are critical to studying and quantifying biological, chemical, and physical processes within the coastal ocean. These observations are to be achieved from a vantage point near 95°–100°W, providing a complete view of North America as well as the adjacent oceans. The SWGs have also endorsed the concept of phased implementation using commercial satellites to reduce mission risk and cost. GEO-CAPE will join the global constellation of geostationary atmospheric chemistry and coastal ocean color sensors planned to be in orbit in the 2020 time frame.

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We characterize the chemical composition of Asian continental outflow observed during the NASA Transport and Chemical Evolution over the Pacific (TRACE‐P) mission during February–April 2001 in the western Pacific using data collected on the NASA DC‐8 aircraft. A significant anthropogenic impact was present in the free troposphere and as far east as 150°E longitude reflecting rapid uplift and transport of continental emissions. Five‐day backward trajectories were utilized to identify five principal Asian source regions of outflow: central, coastal, north‐northwest (NNW), southeast (SE), and west‐southwest (WSW). The maximum mixing ratios for several species, such as CO, C2Cl4, CH3Cl, and hydrocarbons, were more than a factor of 2 larger in the boundary layer of the central and coastal regions due to industrial activity in East Asia. CO was well correlated with C2H2, C2H6, C2Cl4, and CH3Cl at low altitudes in these two regions (r2 ∼ 0.77–0.97). The NNW, WSW, and SE regions were impacted by anthropogenic sources above the boundary layer presumably due to the longer transport distances of air masses to the western Pacific. Frontal and convective lifting of continental emissions was most likely responsible for the high altitude outflow in these three regions. Photochemical processing was influential in each source region resulting in enhanced mixing ratios of O3, PAN, HNO3, H2O2, and CH3OOH. The air masses encountered in all five regions were composed of a complex mixture of photochemically aged air with more recent emissions mixed into the outflow as indicated by enhanced hydrocarbon ratios (C2H2/CO ≥ 3 and C3H8/C2H6 ≥ 0.2). Combustion, industrial activities, and the burning of biofuels and biomass all contributed to the chemical composition of air masses from each source region as demonstrated by the use of C2H2, C2Cl4, and CH3Cl as atmospheric tracers. Mixing ratios of O3, CO, C2H2, C2H6, SO2, and C2Cl4 were compared for the TRACE‐P and PEM‐West B missions. In the more northern regions, O3, CO, and SO2 were higher at low altitudes during TRACE‐P. In general, mixing ratios were fairly similar between the two missions in the southern regions. A comparison between CO/CO2, CO/CH4, C2H6/C3H8, NOx/SO2, and NOy/(SO2 + nss‐SO4) ratios for the five source regions and for the 2000 Asian emissions summary showed very close agreement indicating that Asian emissions were well represented by the TRACE‐P data and the emissions inventory.

[1] We present here results for reactive nitrogen species measured aboard the NASA DC-8 aircraft during the Transport and Chemical Evolution over the Pacific (TRACE-P) mission. The large-scale distributions total reactive nitrogen (NO y,sum = NO + NO 2 + HNO 3 + PAN + C 1 -C 5 alkyl nitrates) and O 3 and CO were better defined in the boundary layer with significant degradation of the relationships as altitude increased. Typically, NO y,sum was enhanced over background levels of $260 pptv by 20-to-30-fold. The ratio C 2 H 2 /CO had values of 1-4 at altitudes up to 10 km and as far eastward as 150°E, implying significant vertical mixing of air parcels followed by rapid advection across the Pacific. Analysis air parcels originating from five principal Asian source regions showed that HNO 3 and PAN dominated NO y,sum . Correlations of NO y,sum with C 2 Cl 4 (urban tracer) were not well defined in any of the source regions, and they were only slightly better with CH 3 Cl (biomass tracer). Air parcels over the western Pacific contained a complex mixture of emission sources that are not easily resolvable as shown by analysis of the Shanghai mega-city plume. It contained an intricate mixture of pollution emissions and exhibited the highest mixing ratios of NO y,sum species observed during TRACE-P. Comparison of tropospheric chemistry between the earlier PEM-West B mission and the recent TRACE-P data showed that in the boundary layer significant increases in the mixing ratios of NO y,sum species have occurred, but the middle and upper troposphere seems to have been affected minimally by increasing emissions on the Asian continent over the last 7 years.

[1] The 10 Be/ 7 Be ratio is a sensitive tracer of atmospheric transport and stratospheretroposphere exchange (STE). Data from five NASA aircraft field missions (PEM: West A and B, Tropics A; SONEX; and SUCCESS) have been assembled to produce the largest data set of 10 Be, 7 Be, and their ratio collected to date (>300 samples). Ratios near 0.60 are indicative of tropospheric air with little stratospheric influence, while higher ratios are found in stratospheric air. Samples from the lower stratosphere were all collected within 2.5 km of the tropopause and had ratios >1.27. Of these lower stratosphere samples only 16% had ratios in excess of 3.0, suggesting that higher ratio air resides away from the tropopause. Seasonality observed in the 10 Be/ 7 Be ratios results from the downwelling of air with elevated ratios from higher in the stratosphere in the spring and summer (midlatitudes) and from the decay of 7 Be during descent in the winter polar vortex (high latitudes). Our results illustrate the complexity of STE and some of the mechanisms through which it occurs, including tropopause folding, mixing associated with subtropical jets, and the effect of synoptic systems such as hurricanes and northeasters. The 10 Be/ 7 Be ratio provides important information beyond that which can be derived from studies that rely on chemical mixing ratios alone.INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0368 Atmospheric Composition and Structure: Troposphereconstituent transport and chemistry; 3362 Meteorology and Atmospheric Dynamics: Stratosphere/troposphere interactions; KEYWORDS: Aerosols, radioisotopes, beryllium, stratosphere-troposphere exchange Citation: Jordan, C. E., J. E. Dibb, and R. C. Finkel, 10 Be/ 7 Be tracer of atmospheric transport and stratosphere-troposphere exchange,