The gradient of meteorological and chemical variables across the tropopause

The downward transport of air through the tropopause can bring substantial amounts of ozone and reactive nitrogen into the upper troposphere. In this cold region of the atmosphere, O3 is particularly effective as a greenhouse gas. As part of the North Dakota Thunderstorm Project in June 1989, the NCAR Sabreliner made five flights through the tropopause. We measured ozone, nitric oxide (NO), total reactive nitrogen (NO(y)), carbon monoxide (CO), and water vapor (H2)), and took grab samples for hydrocarbon (HC) analysis. Hydrocarbons, CO, and H2O, species with sources primarily at the earth's surface, showed a strong concentration decrease with increasing altitude, while O3 and NO(y), species with a source in the stratosphere, showed a strong concentration increase with increasing altitude. Stratospheric concentrations of NO(x), NO(y), and H2O were all high relative to winter observations made during NASA's AASE. We suggest that midlatitude thunderstorms may inject wet, NO-rich air into the lower stratosphere. Calculation based on measured ratios of NO(x) and NO(y) to O3 yield a total flux of reactive nitrogen from the Northern Hemisphere stratosphere into the troposphere of 1 to 2 Tg(N) yr(exp -1) with about 8 percent in the form of NO(x). This value is higher than reported estimates of total stratospheric nitrogen fixation

A 16-yr Comparison of Fine Particle and Aerosol Strong Acidity at the Interface Zone (1,540 m) and Within (452 m) the Planetary Boundary Layer of the Great Gulf and Presidential-Dry River Class I Wildernesses on the Presidential Range, New Hampshire

Mount Washington, NH in the White Mountain National Forest, is flanked to the north-northeast and south by two Class I Wilderness areas, the Great Gulf and Presidential Range-Dry River Wildernesses, respectively. The Clean Air Act protects Class I area natural resource values from air pollution. Aerosol sulfate, a fine particulate component that is often transported long distances, is a known contributor to visibility degradation and acidic deposition. We examined summertime fine particulate aerosol mass and sulfate, strong acidity and ammonium concentrations from 1988 to 2004 on Mount Washington at two elevations, 452 and 1,540 meters (msl). The former site is within, and the latter at the interface of, the planetary boundary layer. Comparisons of sampling interval durations (10 and 24 hours), site vs. site, and different sampling methods are made. We also examine the extent to which aerosol sulfate is neutralized. Ten hour (daytime) compared to 24 hour samples have higher mass and aerosol sulfate concentrations, however paired samples are well correlated. Fine mass concentrations compared between the 452 m and 1,540 m sites (standard temperature and pressure corrected) show a weak positive linear relationship with the later being approximately 34% lower. We attribute the lack of a strong correlation to the facts that the 1,540 m site is commonly at the interface of and even above the regional planetary boundary layer in summer and that it can intercept different air masses relative to the 452 m site. Sulfate is approximately 19% lower at the higher elevation site, but comprises a greater percentage of total fine mass; 42% compared to 35% for the high and low elevation site, respectively. Aerosol strong acidity was found to increase with increasing sulfate concentrations at both sites. At the high elevation site, elevated mass and sulfate concentrations are associated with westerly and southwesterly regional flows

Carbon monoxide measurements at Mace Head, Ireland

The North Atlantic Ocean is bordered by continents which may each, under the influence of seasonal weather patterns, act as sources of natural and anthropogenic trace gas and particulate species. Photochemically active species such as carbon monoxide (CO) react to form ozone (O3), a species of critical importance in global climate change. CO is sparingly soluble in water, and the relatively long lifetime of CO in the troposphere makes this species an ideal tracer of air masses with origin over land. We have measured CO using a nondispersive infrared gas filter correlation analyzer at Mace Head on the west coast of Ireland nearly continuously since August 9, 1991. Measurements of CO were acquired at 20-sec resolution and recorded as 60-sec averages. Daily, monthly, and diurnal variation data characteristics of CO mixing ratios observed at this site are reported. Depending on source regions of air parcels passing over this site, 60-min concentrations of CO range from clean air values of approximately 90 ppbv to values in excess of 300 ppbv. Data characterizing the correlation between 60-min CO and O3 mixing ratio data observed at this site are reported also

Particulate Polycyclic Aromatic Hydrocarbons (PAHs) in the Atlantic and Indian Ocean Atmospheres During INDOEX and AEROSOLs99: Continental Sources to the Marine Atmosphere

Polycyclic aromatic hydrocarbons (PAHs), mutagenic compounds predominantly derived from combustion, have been used as markers of combustion sources to the atmosphere. Marine aerosol collected aboard the NOAA R/V Ronald Brown during the Aerosols99 and the Indian Ocean Experiment (INDOEX) projects was analyzed for PAHs to assess the continental impact of combustion-derived particulate matter on the Atlantic and Indian Ocean atmospheres. PAH concentrations in the Atlantic and southern Indian Ocean atmospheres were consistent and low, ranging from \u3c0.45 pg/m(3) for coronene to 30 pg/m(3) for 9,10-dimethylanthracene. PAH concentrations increased ten fold as the ship crossed the Intertropical Convergence Zone (ITCZ) into the northern Indian Ocean, indicating an increased anthropogenic influence. PAH concentrations over the northern Indian Ocean atmosphere were approximately an order of magnitude greater than those in the northern Atlantic Ocean atmosphere. PAH composition profiles over the northern Indian Ocean were specific to wind regimes and influenced by a combination of biomass and fossil fuel combustion. This was supported by significant correlations between select PAHs and organic carbon (OC), elemental carbon (EC), SO4-2 and K+ for particular wind regimes. Indeno[1,2,3-cd]pyrene/EC ratios used as a combustion source marker suggest that fossil fuel combustion, rather than biomass burning, is the predominant source of PAHs to the Northern Hemisphere Indian Ocean atmosphere. Interestingly, fossil fuel consumption in the Indian sub-continent is a fraction of that in Europe and the United States but the soot and PAH levels in the adjacent Northern Indian Ocean atmosphere are significantly greater than those in the Northern Atlantic atmosphere

Relationship of ozone and carbon monoxide over North America

Observations at sites in eastern North America show a strong correlation between O3 and CO concentrations in summer, with a consistent slope ΔO3/ΔCO ≈ 0.3. Observations in the aged Denver plume at Niwot Ridge, Colorado, also show a strong correlation but with ΔO3/ΔCO = 0.15. These data offer a sensitive test for evaluating the ability of photochemical models to simulate production of O3 over North America and its export to the global atmosphere. Application to the Harvard/Goddard Institute for Space Studies three-dimensional, continental-scale model shows that the model gives a good simulation of the observed O3-CO correlations and of the associated ΔO3/ΔCO. This successful simulation lends support to model estimates of 6 Gmol d−1 for the net O3 production in the U.S. boundary layer in summer (corresponding to a net O3 production efficiency of 5.5, which is the number of O3 molecules produced per molecule of NOx consumed) and 70% for the fraction of the net production that is exported to the global atmosphere. Export of U.S. pollution appears to make a significant contribution to total tropospheric O3 over the northern hemisphere in summer. Simple interpretation of observed ΔO3/ΔCO as an O3/CO anthropogenic enhancement ratio is shown to underestimate substantially anthropogenic O3 production, because O3 and CO concentrations are negatively correlated in the absence of photochemistry. It is also shown that concurrent observations of ΔO3/ΔCO and ΔO3/Δ(NOy-NOx) ratios can be used to impose lower and upper limits on the net O3 production efficiency.Engineering and Applied Science

A Side by Side Comparison of Filter-Based PM(sub 2.5) Measurements at a Suburban Site: A Closure Study

Reliable determination of the effects of air quality on public health and the environment requires accurate measurement of PM(sub 2.5) mass and the individual chemical components of fine aerosols. This study seeks to evaluate PM(sub 2.5) measurements that are part of a newly established national network by comparing them with a more conventional sampling system. Experiments were carried out during 2002 at a suburban site in Maryland, United States, where two samplers from the U.S. Environmental Protection Agency (USEPA) Speciation Trends Network: Met One Speciation Air Sampling System STNS and Thermo Scientific Reference Ambient Air Sampler STNR, two Desert Research Institute Sequential Filter Samplers DRIF, and a continuous TEOM monitor (Thermo Scientific Tapered Element Oscillating Microbalance) were sampling air in parallel. These monitors differ not only in sampling configuration but also in protocol-specific sample analysis procedures. Measurements of PM(sub 2.5) mass and major contributing species were well correlated among the different methods with r-values > 0.8. Despite the good correlations, daily concentrations of PM(sub 2.5) mass and major contributing species were significantly different at the 95% confidence level from 5 to 100% of the time. Larger values of PM(sub 2.5) mass and individual species were generally reported from STNR and STNS. The January STNR average PM(sub 2.5) mass (8.8 (micro)g/per cubic meter) was 1.5 (micro)g/per cubic meter larger than the DRIF average mass. The July STNS average PM(sub 2.5) mass (27.8 (micro)g/per cubic meter) was 3.8 (micro)g/per cubic meter larger than the DRIF average mass. These differences can only be partially accounted for by known random errors. Variations in flow control, face velocity, and sampling artifacts likely influence the measurement of PM(sub 2.5) speciation and mass closure. Simple statistical tests indicate that the current uncertainty estimates used in the STN network may underestimate the actual uncertainty

Analysis of Summertime PM2.5 and haze in the Mid-Atlantic Region

Observations of the mass and chemical composition of particles less than 2.5 #1;m in aerodynamic diameter (PM2.5), light extinction, and meteorology in the urban Baltimore-Washington corridor during July 1999 and July 2000 are presented and analyzed to study summertime haze formation in the mid-Atlantic region. The mass fraction of ammoniated sulfate (SO4 2#2;) and carbonaceous material in PM2.5 were each #3;50% for cleaner air (PM2.5 #4; 10 #1;g/m3) but changed to #3;60% and #3;20%, respectively, for more polluted air (PM2.5 #5; 30 #1;g/m3). This signifies the role of SO4 2#2; in haze formation. Comparisons of data from this study with the Interagency Monitoring of Protected Visual Environments network suggest that SO4 2#2; is more regional than carbonaceous material and originates in part from upwind source regions. The light extinction coefficient is well correlated to PM2.5 mass plus water associated with inorganic salt, leading to a mass extinction efficiency of 7.6 #6; 1.7 m2/g for hydrated aerosol. The most serious haze episode occurring between July 15 and 19, 1999, was characterized by westerly transport and recirculation slowing removal of pollutants. At the peak of this episode, 1-hr PM2.5 concentration reached #3;45 #1;g/m3, visual range dropped to #3;5 km, and aerosol water likely contributed to #3;40% of the light extinction coefficient