Publications

The impact of aircraft emissions on reactive nitrogen in the upper troposphere (UT) and lowermost stratosphere (LS) was estimated using the NO y ‐O 3 correlation obtained during the Subsonic Assessment (SASS) Ozone and Nitrogen Oxide Experiment (SONEX) carried out over the U.S. continent and North Atlantic Flight Corridor (NAFC) region in October and November 1997. To evaluate the large‐scale impact, we made a reference NO y ‐O 3 relationship in air masses, upon which aircraft emissions were considered to have little impact. For this purpose, the integrated input of NO x from aircraft into an air mass along a 10‐day back trajectory (ΔNO y ) was calculated based on the Abatement of Nuisance Caused by Air Traffic/European Commission (ANCAT/EC2) emission inventory. The excess NO y ( d NO y ) was calculated from the observed NO y and the reference NO y ‐O 3 relationship. As a result, a weak positive correlation was found between the d NO y and ΔNO y , and d NO y and NO x /NO y values, while no positive correlation between the d NO y and CO values was found, suggesting that d NO y values can be used as a measure of the NO x input from aircraft emissions. The excess NO y values calculated from another NO y ‐O 3 reference relationship made using in situ condensation nuclei data also agreed with these d NO y values, within the uncertainties. At the NAFC region (45°N–60°N) the median value of d NO y in the troposphere increased with altitude above 9 km and reached 70 parts per trillion by volume (pptv) (20% of NO y ) at 11 km. The excess NO x was estimated to be about half of the d NO y values, corresponding to 30% of the observed NO x level. Higher d NO y values were generally found in air masses where O 3 = 75–125 ppbv, suggesting a more pronounced effect around the tropopause. The median value of d NO y in the stratosphere at the NAFC region at 8.5–11.5 km was about 120 pptv. The higher d NO y values in the LS were probably due to the accumulated effect of aircraft emissions, given the long residence time of affected air in the LS. Similar d NO y values were also obtained in air masses sampled over the U.S. continent.

Abstract. Boreal regions comprise about 17% of the global land area, and they both affect and are influenced by climate change. To better understand boreal forest fire emissions and plume evolution, 947 whole air samples were collected aboard the NASA DC-8 research aircraft in summer 2008 as part of the ARCTAS-B field mission, and analyzed for 79 non-methane volatile organic compounds (NMVOCs) using gas chromatography. Together with simultaneous measurements of CO2, CO, CH4, CH2O, NO2, NO, HCN and CH3CN, these measurements represent the most comprehensive assessment of trace gas emissions from boreal forest fires to date. Based on 105 air samples collected in fresh Canadian smoke plumes, 57 of the 80 measured NMVOCs (including CH2O) were emitted from the fires, including 45 species that were quantified from boreal forest fires for the first time. After CO2, CO and CH4, the largest emission factors (EFs) for individual species were formaldehyde (2.1 ± 0.2 g kg−1), followed by methanol, NO2, HCN, ethene, α-pinene, β-pinene, ethane, benzene, propene, acetone and CH3CN. Globally, we estimate that boreal forest fires release 2.4 ± 0.6 Tg C yr−1 in the form of NMVOCs, with approximately 41% of the carbon released as C1–C2 NMVOCs and 21% as pinenes. These are the first reported field measurements of monoterpene emissions from boreal forest fires, and we speculate that the pinenes, which are relatively heavy molecules, were detected in the fire plumes as the result of distillation of stored terpenes as the vegetation is heated. Their inclusion in smoke chemistry models is expected to improve model predictions of secondary organic aerosol (SOA) formation. The fire-averaged EF of dichloromethane or CH2Cl2, (6.9 ± 8.6) ×10−4 g kg−1, was not significantly different from zero and supports recent findings that its global biomass burning source appears to have been overestimated. Similarly, we found no evidence for emissions of chloroform (CHCl3) or methyl chloroform (CH3CCl3) from boreal forest fires. The speciated hydrocarbon measurements presented here show the importance of carbon released by short-chain NMVOCs, the strong contribution of pinene emissions from boreal forest fires, and the wide range of compound classes in the most abundantly emitted NMVOCs, all of which can be used to improve biomass burning inventories in local/global models and reduce uncertainties in model estimates of trace gas emissions and their impact on the atmosphere.

In-situ measurements of a large number of trace chemicals from upper troposphere/lower stratosphere (UT/LS) were performed with the NASA DC-8 aircraft during February/March 1994 over the Pacific Ocean (10 S to 60 N). Mixing ratios in the UT were relatively low in the warm tropical and subtropical air south of the polar jetstream (approx. =28 N) but increased sharply with latitude in the cold polar air north of the jetstream. At about 45 N, high concentrations of PAN (300 ppt) coexisted with extremely low (approx. = 20 ppt) concentrations of NOx. Elevated NOx levels in the UT did not always correspond to continental outflow conditions. Deepest penetrations into the stratosphere (550 ppb O3, 279 ppb NOx, and 350 K potential temperature) corresponded to a region that has been defined as the 'lowermost stratosphere' (LS) by Holton et al. Analysis of data shows that the mixing ratios of long-lived tracer species (e.g., CH4, HNO3, NOy, CFCs, HCFCs) are linearly correlated with those of O3 and N2O. A delta-NOY/delta-O3 of 0.0054 ppb/ppb and delta-NOy/delta-N2O of -0.081 ppb/ppb is in good agreement with other reported measurements from the DC-8. These slopes are however, somewhat steeper than those reported from the ER-2 studies. We find that the reactive nitrogen budget in the UT/LS is largely balanced with shortfalls that are no greater than 15%. A number of oxygenated species (e.g., acetone, H2O2) are present and may provide an important in-situ source of HOx in the UT/LS region.

Abstract. A case of continental outflow from the United States (US) was examined using airborne measurements from NASA DC-8 flight 13 during the Intercontinental Chemical Transport Experiment – North America (INTEX-NA). Mixing ratios of methane (CH4) and carbon monoxide (CO) at 8–11 km altitude over the North Atlantic were elevated to 1843 ppbv and 134 ppbv respectively, while those of carbon dioxide (CO2) and carbonyl sulfide (COS) were reduced to 372.4 ppmv and 411 pptv respectively. In this region, urban and industrial influences were evidenced by elevated mixing ratios and good linear relationships between urban and industrial tracers compared to North Atlantic background air. Moreover, low mixing ratios and a good correlation between COS and CO2 showed a fingerprint of terrestrial uptake and minimal dilution during rapid transport over a 1–2 day time period. Analysis of synoptic conditions, backward trajectories, and photochemical aging estimates based on C3H8/C2H6 strongly suggested that elevated anthropogenic tracers in the upper troposphere of the flight region were the result of transport via convection and warm conveyor belt (WCB) uplifting of boundary layer air over the southeastern US. This mechanism is supported by the similar slope values of linear correlations between long-lived (months) anthropogenic tracers (e.g., C2Cl4 and CHCl3) from the flight region and the planetary boundary layer in the southeastern US. In addition, the aircraft measurements suggest that outflow from the US augmented the entire tropospheric column at mid-latitudes over the North Atlantic. Overall, the flight 13 data demonstrate a pervasive impact of US anthropogenic emissions on the troposphere over the North Atlantic.

Abstract The inorganic fraction of fine particles affects numerous physicochemical processes in the atmosphere. However, there is large uncertainty in its burden and composition due to limited global measurements. Here, we present observations from eleven different aircraft campaigns from around the globe and investigate how aerosol pH and ammonium balance change from polluted to remote regions, such as over the oceans. Both parameters show increasing acidity with remoteness, at all altitudes, with pH decreasing from about 3 to about −1 and ammonium balance decreasing from almost 1 to nearly 0. We compare these observations against nine widely used chemical transport models and find that the simulations show more scatter (generally R 2 < 0.50) and typically predict less acidic aerosol in the most remote regions. These differences in observations and predictions are likely to result in underestimating the model-predicted direct radiative cooling effect for sulfate, nitrate, and ammonium aerosol by 15–39%.

MethodsThis section presents the details of the measurements used in this study. O3 and NOx measured by chemiluminescenceO3 and NOx were measured by chemiluminescence (CL) (Bourgeois et al., 2022;Bourgeois et al., 2021).Ambient O3 was reacted with pure NO, and the resulting CL signal was detected, amplified, and converted to ambient levels based on ground and in-flight calibrations by standard additions of O3 generated on board the aircraft.Ambient NO was reacted with onboard-generated O3 and the resulting CL signal was converted to ambient levels in a similar method as for O3, but calibrated with standard additions from an NO standard.NO2 was converted to NO by UV photolysis at 385 nm, and detected similarly to NO. O3 , NO, and NO2 were reported at 1-Hz with an uncertainty and precision of ±(2% + 15 pptv), ±(4% + 6 pptv), and ±(7% + 20 pptv) for O3, NO, and NO2, respectively. CO and CH4 measured by laser absorption spectroscopyCO and CH4 were measured using the Differential Absorption Carbon monOxide Measurement DACOM instrument (Sachse et al., 1987).This instrument utilizes three single-mode tunable diode lasers, with CO measured using a quantum cascade laser (QCL) at approximately 4.7 µm and CH4 with an interband cascade laser (ICL) at ~3.3 µm.The DACOM instrument was calibrated, using gases supplied by NOAA ESRL, nominally on a 4-minute clock, but often advanced or delayed in time to avoid calibrating during fire plume encounters.Calibrations provided both slope and intercept values tying signals to species concentrations.Post-campaign analysis of the DACOM CO data indicated that measurement precision (1σ) was approximately 0.1% at 1 Hz and 0.14% at 5 Hz.CO

Ozone (O 3 ) and aerosol scattering ratio profiles were obtained from airborne lidar measurements on thirty‐eight flights over seven deployments covering the latitudes of 40°–85°N between 4 February and 23 May 2000 as part of the Tropospheric Ozone Production about the Spring Equinox (TOPSE) field experiment. Each deployment started from Broomfield, Colorado, with bases in Churchill, Canada, and on most deployments, Thule Air Base, Greenland. Nadir and zenith lidar O 3 measurements were combined with in situ O 3 measurements to produce vertically continuous O 3 profiles from near the surface to above the tropopause. Potential vorticity (PV) distributions along the flight track were obtained from several different meteorological analyses. Ozone, aerosol, and PV distributions were used together to identify the presence of pollution plumes and stratospheric intrusions. Ozone was found to increase in the middle free troposphere (4–6 km) at high latitudes (60°–85°N) by an average of 4.6 ppbv/mo (parts per billion by volume per month) from about 54 ppbv in early February to over 72 ppbv in mid‐May. The average aerosol scattering ratios at 1064 nm in the same region increased rapidly at an average rate of 0.36/mo from about 0.38 to over 1.7. Ozone and aerosol scattering were highly correlated over the entire field experiment, and PV and beryllium ( 7 Be) showed no significant positive trend over the same period. The primary cause of the observed O 3 increase in the mid troposphere at high latitudes was determined to be the photochemical production of O 3 in pollution plumes with less than 20% of the increase from stratospherically‐derived O 3 .

Airborne measurements of the emissions of gases and particles from 19 individual forest, cerrado, and pasture fires in Brazil were obtained during the Smoke, Clouds, and Radiation‐Brazil (SCAR‐B) study in August‐September 1995. Emission factors were determined for a number of major and minor gaseous and particulate species, including carbon dioxide, carbon monoxide, sulfur dioxide, nitrogen oxides, methane, nonmethane hydrocarbons, halocarbons, particulate (black and organic) carbon, and particulate ionic species. The magnitude of the emission factors for gaseous species were determined primarily by the relative amounts of flaming and smoldering combustion, rather than differences in vegetation type. Hydrocarbons and halocarbons were well correlated with CO, which is indicative of emissions primarily associated with smoldering combustion. Although there was large variability between fires, higher emission factors for SO 2 and NO χ were associated with an increased ratio of flaming to smoldering combustion; this could be due to variations in the amounts of sulfur and nitrogen in the fuels. Emission factors for particles were not so clearly associated with smoldering combustion as those for hydrocarbons. The emission factors measured in this study are similar to those measured previously in Brazil and Africa. However, particle emission factors from fires in Brazil appear to be roughly 20 to 40% lower than those from North American boreal forest fires.