Mount Bachelor Observatory Research Articles

Investigation of the Parameters Influencing Baseline Ozone in the Western United States: A Statistical Modeling Approach

Ground-level ozone (O3) is a key atmospheric gas that controls the oxidizing capacity of the atmosphere and has significant health and environmental implications. Due to ongoing reductions in the concentrations of O3 precursors, it is important to assess the variables influencing baseline O3 to inform pollution control strategies. This study uses a statistical model to characterize daily peak 8 h O3 concentrations at the Mount Bachelor Observatory (MBO), a rural mountaintop research station in central Oregon, from 2006–2020. The model was constrained by seven predictive variables: year, day-of-year, relative humidity (RH), aerosol scattering, carbon monoxide (CO), water vapor (WV) mixing ratio, and tropopause pressure. RH, aerosol scattering, CO, and WV mixing ratio were measured at MBO, and tropopause pressure was measured via satellite. For the full 15-year period, the model represents 61% of the variance in daily peak 8 h O3, and all predictive variables have a statistically significant (p < 0.05) impact on daily peak 8 h O3 concentrations. Our results show that daily peak 8 h O3 concentrations at MBO are well-predicted by the model, thereby providing insight into what affects baseline O3 levels at a rural site on the west coast of North America.

Comparison of Filter-based Absorption Measurements of Biomass Burning Aerosol and Background Aerosol at the Mt. Bachelor Observatory

ABSTRACT In this study we evaluate the recently upgraded aethalometer (AE33) and the newly released tricolor absorption photometer (TAP) with respect to their response to wildfire aerosol plumes during their deployment at the Mount Bachelor Observatory (MBO; 2763 m a.s.l.) in central Oregon, USA, during the summer of 2016. While both instruments use similar methodology (i.e., light extinction through an aerosol-laden filter), each has a unique set of correction schemes to address artifacts originating from filter loading, scattering from captured aerosol particles, and multiple scattering effects of the filter fibers. We also utilize a Single Particle Soot Photometer (SP2) to determine refractory black carbon (rBC) in these air masses. In addition to comparing the AE33 filter-loading correction methodology to previously published aethalometer correction schemes, we also compare the AE33 to the correction schemes used for the TAP and evaluate the degree to which the different correction factors influence the derived absorption Angstrom exponents (AAE) and mass absorption cross sections (MACs). We find that while the different correction factors for either the AE33 or TAP do exert an influence on the derived MACs, AAEs exhibit the most sensitivity to the correction schemes. Our study finds that using the AE33 manufacturer’s recommended settings results in aerosol light absorption coefficients that are 3.4 to 4 times greater than the aerosol light absorption coefficients reported by the TAP. We calculated a correction factor (Cf) of 4.35 for the AE33 by normalizing the AE33 to match the TAP. The uncorrected AE33 also gives equivalent black carbon (eBC) values that are approximately 2 times the rBC measured by the SP2 instrument. We also find that biomass burning aerosols result in significant MAC enhancements, particularly at lower wavelengths, which is attributable to brown carbon (BrC).

Free tropospheric aerosols at the Mt. Bachelor Observatory: more oxidized and higher sulfate content compared to boundary layer aerosols

Abstract. Understanding the properties and life cycle processes of aerosol particles in regional air masses is crucial for constraining the climate impacts of aerosols on a global scale. In this study, characteristics of aerosols in the boundary layer (BL) and free troposphere (FT) of a remote continental region in the western US were studied using a high-resolution time-of-flight aerosol mass spectrometer (HR-AMS) deployed at the Mount Bachelor Observatory (MBO; 2763 m a.s.l.) in central Oregon in summer 2013. In the absence of wildfire influence, the average (±1σ) concentration of non-refractory submicrometer particulate matter (NR-PM1) at MBO was 2.8 (±2.8) µg m−3 and 84 % of the mass was organic. The other NR-PM1 components were sulfate (11 %), ammonium (2.8 %), and nitrate (0.9 %). The organic aerosol (OA) at MBO from these clean periods showed clear diurnal variations driven by the boundary layer dynamics with significantly higher concentrations occurring during daytime, upslope conditions. NR-PM1 contained a higher mass fraction of sulfate and was frequently acidic when MBO resided in the FT. In addition, OA in the FT was found to be highly oxidized (average O∕C of 1.17) with low volatility while OA in BL-influenced air masses was moderately oxidized (average O∕C of 0.67) and semivolatile. There are indications that the BL-influenced OA observed at MBO was more enriched in organonitrates and organosulfur compounds (e.g., MSA) and appeared to be representative of biogenic secondary organic aerosol (SOA) originated in the BL. A summary of the chemical compositions of NR-PM1 measured at a number of other high-altitude locations in the world is presented and similar contrasts between FT and BL aerosols were observed. The significant compositional and physical differences observed between FT and BL aerosols may have important implications for understanding the climate effects of regional background aerosols.

Impact of Biomass Burning Plumes on Photolysis Rates and Ozone Formation at the Mount Bachelor Observatory

AbstractIn this paper, we examine biomass burning (BB) events at the Mt. Bachelor Observatory (MBO) during the summer of 2015. We explored the photochemical environment in these BB plumes, which remains poorly understood. Because we are interested in understanding the effect of aerosols only (as opposed to the combined effect of aerosols and clouds), we carefully selected three cloud‐free days in August and investigate the photochemistry in these plumes. At local midday (solar zenith angle (SZA) = 35°), j(NO2) values were slightly higher (0.2–1.8%) in the smoky days compared to the smoke‐free day, presumably due to enhanced scattering by the smoke aerosols. At higher SZA (70°), BB aerosols decrease j(NO2) by 14–21%. We also observe a greater decrease in the actinic flux at 310–350 nm, compared to 360–420 nm, presumably due to absorption in the UV by brown carbon. We compare our measurements with results from the Tropospheric Ultraviolet‐Visible v.5.2 model. As expected, we find a good agreement (to within 6%) during cloud‐free conditions. Finally, we use the extended Leighton relationship and a photochemical model (Aerosol Simulation Program v.2.1) to estimate midday HO2 and RO2 concentrations and ozone production rates (P(O3)) in the fire plumes. We observe that Leighton‐derived HO2 and RO2 values (49–185 pptv) and instantaneous P(O3) (2.0–3.6 ppbv/h) are higher than the results from the photochemical model.

Comparison of ultraviolet absorbance and NO-chemiluminescence for ozone measurement in wildfire plumes at the Mount Bachelor Observatory

The goal of this paper is to evaluate the accuracy of the commonly used ozone (O3) instrument (the ultraviolet (UV) photometer) against a Federal Reference Method (Nitric Oxide –chemiluminescence) for ozone measurement in wildfire smoke plumes. We carried out simultaneous ozone measurement with two UV O3 photometers and one nitric oxide–chemiluminescence (NO-CL) ozone detectors during wildfire season (Aug. 1–Sept. 30) in 2015 at the Mount Bachelor Observatory (MBO, 2763 m above mean sea level, Oregon, USA). The UV O3 shows good agreement and excellent correlation to NO-CL O3, with linear regression slopes close to unity and R2 of 0.92 for 1-h average data and R2 of 0.93 for O3 daily maximum 8-h average (MDA8). During this two-month period we identified 35 wildfire events. Ozone enhancements in those wildfire plumes measured by NO-CL O3 and UV O3 monitors also show good agreement and excellent linear correlation, with a slope and R2 of 1.03 and 0.86 for O3 enhancements (ΔO3) and 1.00 and 0.98 for carbon monoxide (CO)-normalized ozone enhancement ratios (ΔO3/ΔCO), respectively. Overall, the UV O3 was found to have a positive bias of 4.7 ± 2.8 ppbv compared to the NO-CL O3. The O3 bias between NO-CL O3 and UV O3 is independent of wildfire plume tracers such as CO, particulate matter (PM1), aerosol scattering, and ultrafine particles. The results demonstrate that the UV O3 absorbance method is reliable, even in highly concentrated wildfire plumes.

Meteorological anomalies lead to elevated O3 in the western U.S. in June 2015

AbstractIn winter through early summer of 2014–2015, temperatures in the western U.S. were substantially enhanced due to a persistent high‐pressure ridge and warm water in the northeastern Pacific Ocean. Concurrently, monthly averaged maximum daily 8 h average (MDA8) O3 in June 2015 was enhanced by 3–13 ppb across a large portion of the western U.S. At the Mount Bachelor Observatory (2.8 km above sea level) in central Oregon, O3 in June 2015 was enhanced by 11 ppbv compared to the long‐term mean. Some urban areas had many days in June 2015 with MDA8 values above the current air quality threshold of 70 ppbv. We show that the high O3 was associated with enhanced temperatures, reduced cloud fraction, increased stagnation, and increased biogenic emissions. The data in June 2015 show enhanced ΔO3/Δtemperature slopes at several sites, compared to previous June data, due to these multiple factors.

Interannual Variability in Baseline Ozone and Its Relationship to Surface Ozone in the Western U.S.

Baseline ozone refers to observed concentrations of tropospheric ozone at sites that have a negligible influence from local emissions. The Mount Bachelor Observatory (MBO) was established in 2004 to examine baseline air masses as they arrive to North America from the west. In May 2012, we observed an O3 increase of 2.0-8.5 ppbv in monthly average maximum daily 8-hour average O3 mixing ratio (MDA8 O3) at MBO and numerous other sites in the western U.S. compared to previous years. This shift in the O3 distribution had an impact on the number of exceedance days. We also observed a good correlation between daily MDA8 variations at MBO and at downwind sites. This suggests that under specific meteorological conditions, synoptic variation in O3 at MBO can be observed at other surface sites in the western U.S. At MBO, the elevated O3 concentrations in May 2012 are associated with low CO values and low water vapor values, consistent with transport from the upper troposphere/lower stratosphere (UT/LS). Furthermore, the Real-time Air Quality Modeling System (RAQMS) analyses indicate that a large flux of O3 from the UT/LS in May 2012 contributed to the observed enhanced O3 across the western U.S. Our results suggest that a network of mountaintop observations, LiDAR and satellite observations of O3 could provide key data on daily and interannual variations in baseline O3.

Particulate Matter, Ozone, and Nitrogen Species in Aged Wildfire Plumes Observed at the Mount Bachelor Observatory

ABSTRACTDuring the summer of 2012 and 2013, we measured carbon monoxide (CO), carbon dioxide (CO2), ozone (O3), nitrogen oxides (NOx), reactive nitrogen (NOy), peroxyacetyl nitrate (PAN), aerosol scattering (σsp) and absorption, elemental and organic carbon (EC and OC), and aerosol chemistry at the Mount Bachelor Observatory (2.8 km above sea level, Oregon, US). Here we analyze 23 of the individual plumes from regional wildfires to better understand production and loss of aerosols and gaseous species. We also developed a new method to calculate enhancement ratios and Modified Combustion Efficiency (MCE), which takes into account possible changes in background concentrations during transport. We compared this new method to existing methods for calculating enhancement ratios. The MCE values ranged from 0.79–0.98, ΔO3/ΔCO ranged from 0.01–0.07 ppbv ppbv–1, Δσsp/ΔCO ranged from 0.23–1.32 Mm–1 (at STP) ppbv–1, ΔNOy/ΔCO ranged from 2.89–12.82 pptv ppbv–1, and ΔPAN/ΔCO ranged from 1.46–6.25 pptv ppbv–1. A comparison of three different methods to calculate enhancement ratios (ER) showed that the methods generally resulted in similar Δσsp/ΔCO, ΔNOy/ΔCO, and ΔPAN/ΔCO; however, there was a significant bias between the methods when calculating ΔO3/ΔCO due to the small absolute enhancement of O3 in the plumes. The ΔO3/ΔCO ERs calculated using two common methods were biased low (~20–30%) when compared to the new proposed method. Two pieces of evidence suggest moderate secondary particulate formation in many of the plumes studied: 1) mean observed ΔOC/ΔCO2 was 0.028 g particulate-C gC–1 (as CO2)—27% higher than the midpoint of the biomass burning emission ratio range reported by a recent review—and 2) single scattering albedo (ω) was relatively constant at all MCE values, in contrast with results for fresh plumes. The observed NOx, PAN, and aerosol nitrate represented 6–48%, 25–57%, and 20–69% of the observed NOy in the aged plumes, respectively, and other species represented on average 11% of the observed NOy.

Relative Influence of Trans-Pacific and Regional Atmospheric Transport of PAHs in the Pacific Northwest, U.S.

The relative influences of trans-Pacific and regional atmospheric transport on measured concentrations of polycyclic aromatic hydrocarbons (PAHs), PAH derivatives (nitro- (NPAH) and oxy-(OPAH)), organic carbon (OC), and particulate matter (PM) less than 2.5 μm in diameter (PM2.5) were investigated in the Pacific Northwest, U.S. in 2010–2011. Ambient high volume PM2.5 air samples were collected at two sites in the Pacific Northwest: (1.) Mount Bachelor Observatory (MBO) in the Oregon Cascade Range (2763 m above sea level (asl)) and 2.) Confederated Tribes of the Umatilla Indian Reservation (CTUIR) in the Columbia River Gorge (CRG) (954 m asl). At MBO, the 1,8-dinitropyrene concentration was significantly positively correlated with the time a sampled air mass spent over Asia, suggesting that this NPAH may be a good marker for trans-Pacific atmospheric transport. At CTUIR, NOx, CO2, and SO2 emissions from a 585 MW coal fired power plant, in Boardman OR, were found to be significantly positively correlated with PAH, OPAH, NPAH, OC, and PM2.5 concentrations. By comparing the Boardman Plant operational time frames when the plant was operating to when it was shut down, the plant was found to contribute a large percentage of the measured PAH (67%), NPAH (91%), OPAH (54%), PM2.5 (39%), and OC (38%) concentrations at CTUIR and the CRG prior to Spring 2011 and likely masked trans-Pacific atmospheric transport events to the CRG. Upgrades installed to the Boardman Plant in the spring of 2011 dramatically reduced the plant’s contribution to PAH and OPAH concentrations (by ∼72% and ∼40%, respectively) at CTUIR and the CRG, but not NPAH, PM2.5 or OC concentrations.

Influence of background particulate matter (PM) on urban air quality in the Pacific Northwest

Elevated particulate matter concentrations due to Asian long-range transport (LRT) are frequently observed in the free troposphere (FT) above the Pacific Northwest, U.S. Transport of this aerosol from the FT to the boundary layer (BL) and its effect to local air quality remain poorly constrained. We used data collected at the Mount Bachelor observatory (MBO, 2.8 km a.s.l) and from ground stations in the Pacific Northwest to study transport of fine particulate matter (PM) from the FT to the BL. During Asian LRT episodes PM concentrations were clearly elevated above the corresponding monthly averages at MBO as well as at low elevation sites across Washington and Oregon. Also, a clear correlation between MBO and low elevation sites was observed, indicating that LRT episodes are seen in both the FT and BL. In addition, drum impactor measurements show that the chemical composition of PM at MBO was similar to that measured at the BL sites. Using a simple regression model, we estimate that during springtime, when the transport from Asia is most effective, the contribution of Asian sources to PM2.5 in clean background areas of the Pacific Northwest was on average 1.7 μg m−3 (representing approximately 50–80% of PM). The influence of LRT PM was also seen in measurement stations situated in the urban and urban background areas. However, the fraction of LRT PM was less pronounced (36–50% of PM) due to larger local emissions in the urban areas.

Influence of daily variations in baseline ozone on urban air quality in the United States Pacific Northwest

We examine the influence of daily variations in baseline ozone (O3) on urban air quality in the U.S. Pacific Northwest (PNW) during 2004 to 2010 through two analyses: (1) transport of free tropospheric (FT) O3 from Mount Bachelor Observatory (MBO) to Boise, Idaho; and (2) transport of marine boundary layer (MBL) O3 from Cheeka Peak (CP) to Enumclaw, Washington. Both Boise and Enumclaw experience days with maximum daily 8 hour averages of O3 (MDA8) exceeding U.S. standards. Backward trajectory cluster analyses identify days when FT and MBL O3 strongly influence MDA8 in Boise and Enumclaw. On these days, MBO and CP O3 observations explain 40% and 69% of the variations in Boise and Enumclaw MDA8, respectively. Bivariate regressions for Boise/MBO and Enumclaw/CP have slopes of 0.52 ± 0.16 and 1.04 ± 0.08, respectively, representing the differing interplay of O3 dilution, production, and loss during FT to boundary layer transport (Boise/MBO) and fast boundary layer transport (Enumclaw/CP). AIRPACT‐3/CMAQ (Air Indicator Report for Public Access and Community Tracking version 3/Community Multi‐scale Air Quality model) high‐resolution air‐quality simulation results demonstrate how transport of O3 from the FT above MBO contributes to elevated O3 at Boise. Average MDA8 O3 in Boise is higher than in Enumclaw due to site elevation and greater entrainment of FT air masses, a finding likely applicable to other PNW sites. Days with high baseline influence at Boise and Enumclaw have lower average MDA8 O3 than other days; however, some of these days would still exceed the U.S. standard if it is substantially tightened in 2013, highlighting the increasing importance of FT O3 influence on urban MDA8.

Ozone and particulate matter enhancements from regional wildfires observed at Mount Bachelor during 2004–2011

We report observations of normalized enhancement ratios (NER) for 32 wildfires measured at Mount Bachelor Observatory in central Oregon during June–September 2004–2011. All 32 plumes resulted from wildfires originating in the western United States and Canada. The observed NER of PM1 (particulate matter < 1 micron) to carbon monoxide (ΔPM1/ΔCO) ranged from 0.06 to 0.42 μg m−3 ppbv−1. The NER of ozone to CO (ΔO3/ΔCO) ranged from 0.01 to 0.51 ppbv ppbv−1 for the 13 observed plumes with a significant ΔO3/ΔCO NER (p ≤ 0.01, R2 ≥ 0.30). For wildfire plumes transported <540 km, or approximately <2 days, the ΔPM1/ΔCO NER is found to increase with increasing distance, suggesting that there is significant secondary organic aerosol (SOA) production in these plumes. However, two plumes transported over greater time periods have relatively low ΔPM1/ΔCO NER, indicating that PM1 loss is greater than SOA production in these plumes. Of the three plumes transported the longest distance to MBO, only two have significant O3 production. These two plumes were transported in boundary layer air masses, while the third was transported in a free tropospheric air mass, suggesting that conversion of nitrogen oxides (NOX) to peroxyacetyl nitrate (PAN) may be a factor affecting O3 production in these plumes. Two wildfire plumes are mixed with urban emissions from the Seattle/Tacoma metropolitan area, and have relatively higher ΔO3/ΔCO NER than other wildfire plumes transported over similar distances.

Optical and chemical properties of aerosols transported to Mount Bachelor during spring 2010

[1] We report on springtime 2010 observations of aerosol optical properties and size-resolved elemental composition from Mount Bachelor Observatory (MBO; 2763 meters above sea level). Observations included multiwavelength aerosol scattering and absorption, made with a nephelometer and a particle soot absorption photometer, and size-resolved composition, made using a rotating DRUM impactor with substrates analyzed by synchrotron X-ray fluorescence. Our main tool for investigating variability in composition was empirical orthogonal function (EOF) analysis. In April, dust and sulfate explained 96% of the variance in the observed fine composition and accounted for the majority of the fine mode scattering. Three coincident Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation overpasses also identified aerosol layers classified as dust or polluted dust over MBO. Later in the spring, we deduce that organics and nitrate comprised more than 50% of the submicrometer aerosol mass. We used the EOF analysis to identify systematic relationships between composition and optical properties. We observed dust accompanied by anthropogenic pollutants including sulfate. When present, dust aerosol controlled ∼30% of the variability in the wavelength dependence of fine mode scattering. Many of the samples containing sulfate had absorption Angstrom exponents near 1, suggesting black carbon was also present. Most of the sulfate was in the fine mode, but sulfate was also observed on coarse aerosols, and we inferred that much of the coarse sulfur was coated on the dust or had formed CaSO4 during transport. The relationships between Fe, Ca, Al, and Si observed at MBO were consistent with previous observations of Asian dust transported to North America.

Optical properties of aged Asian aerosols observed over the U.S. Pacific Northwest

A suite of gas‐phase and aerosol measurements were made during spring 2008 and spring 2009 at the Mount Bachelor Observatory (2763 masl), located in Oregon. Here we focus on multiwavelength observations of low RH submicron (μm) aerosol scattering (σsp) and absorption (σap), made with an integrating nephelometer and a particle soot absorption photometer. Using a combination of in situ observations, trajectory calculations and satellite observations, we identified seven plumes of Asian origin. These plumes included many of the highest σsp (34.8 Mm−1) and σap (5.7 Mm−1) hourly average values observed at MBO over the 2008 and 2009 campaigns. Of interest in this analysis is (1) whether the intensive optical properties differ between these seven plumes, (2) whether these differences can be linked to differences in composition, and (3) whether the intensive optical properties change during transpacific transport. Results show that the plumes clustered in terms of their optical properties; plumes hypothesized to contain a large fraction of mineral dust were the most distinct. We observed variability between plumes in the scattering Ångström (Ås) exponent. The average submicrometer Ås for all seven plumes was significantly larger than the same parameter observed closer to Asia. Therefore, we hypothesize that the aerosol size distribution shifts toward smaller particles during transpacific transport. The average submicrometer low‐RH aerosol single scatter albedo (ω) observed at MBO (0.88) was slightly larger than previous observations closer to the Asian coast, and the average backscatter fraction (b) was smaller, on the order of 20%.

Particulate mercury emissions in regional wildfire plumes observed at the Mount Bachelor Observatory

Atmospheric mercury is composed primarily of Hg 0 (>95%), but Hg +2 and particle bound mercury are also found in some environments. The three forms of mercury were measured at the Mount Bachelor Observatory beginning in 2005. Using data gathered from 2005 to 2007, 15 periods were identified during which PHg was above the instrument detection limit of 3 pg m −3 for nine or more consecutive hours. Peak PHg concentrations ranged from 6.0 to 44.3 pg m −3. During these events, PHg is strongly correlated with CO and sub-micron aerosol scatter coefficient (typically R 2 > 0.6). Our data suggest that the 15 PHg events were likely due to regional wildfires in California and Oregon. Wildfires were identified as the primary PHg source using a combination of air-mass back-trajectories, MODIS satellite data, and chemical and physical tracers of combustion. Slopes of the PHg/σ sp and PHg/CO relationships ranged from 0.20 to 1.57 pg (Mm −1) −1 and 0.11 to 0.61 pg m −3 ppb −1, respectively. The range of slopes may indicate different types of burning (e.g. flaming vs. smoldering), differing amounts of chemical processing, different fuel sources, or different physical parameters such as the plume injection height. The slopes provide constraints for the relationship between PHg, CO, and aerosol scatter from wildfires. Asian long-range transport was not a source of PHg but we cannot rule out the possibility of local U.S. industrial sources of PHg for some of the events. Assuming our observations are representative of global fire emissions, we estimate that PHg represents 15% of the total mercury released from wildfires and is a source of PHg comparable to anthropogenic sources.

Model estimate of mercury emission from natural sources in East Asia

East Asia is one of the largest source regions that release mercury into the atmosphere. Although extensive studies have been devoted to estimating the anthropogenic mercury emission, little is known about mercury emission from natural sources in the region. In this study, we adapt the algorithms developed previously, coupled with detailed GIS data and satellite LAI products, to estimate mercury emission from natural sources including vegetation, soil, and water surfaces in an East Asian domain containing 164 × 97 grid cells at a spatial resolution of 36 km. Seasonal simulations were performed to project the annual emission quantity. The simulated emission shows strong diurnal and seasonal variations due to meteorology and vegetation coverage. The annual emission in the form of gaseous elemental mercury (GEM) from the domain in 2001 is estimated to be 834 Mg, with 462 Mg contributed from China. The estimated GEM emission is comparable to the reported anthropogenic emission of 575 ± 261 Mg (56% GEM, 32% reactive gaseous mercury, 12% particulate mercury; Wu, Y., Wang, S., Streets, D.G., Hao, J., Chan, M., Jiang, J., 2006. Trends in anthropogenic mercury emissions in China from 1995 to 2003. Environmental Science & Technology 40, 5312–5318) in China for the year 2001, and dominates the anthropogenic emission during the warm season. Combining the anthropogenic and natural emission estimates, the total mercury emission from China is 776–1298 Mg, with GEM being in the range of 660–1000 Mg. The latter is similar to the GEM emission quantity inferred from aircraft measurement (765 Mg; Friedli, H.R., Radke, L.F., Prescott, R., Li, P., Woo, J.-H., Carmichael, G.R., 2004. Mercury in the atmosphere around Japan, Korea and China as observed during the 2001 ACE Asia field campaign: measurements, distributions, sources, and implications. Journal of Geophysical Research 109, D19 S25) and modeling estimate (1140 Mg; Pan, L., Chai, T., Carmichael, G.R., Tang, Y., Streets, G.G., Woo, J.-H., Friedli, H.R., Radke, L.F., 2007a. Top-down estimate of mercury emissions in China using four-dimensional variational data assimilation. Atmospheric Environment 41, 2804–2819) in China for the year 2001. The estimated natural emission helps explain the gap between the anthropogenic emission estimates based on activity data (e.g., Pacyna, J.M., Pacyna, E., Steenhuisen, F., Wilson, S., 2006. Global anthropogenic mercury emission inventory for 2000. Atmospheric Environment 40, 4048–4063; Wu, Y., Wang, S., Streets, D.G., Hao, J., Chan, M., Jiang, J., 2006. Trends in anthropogenic mercury emissions in China from 1995 to 2003. Environmental Science & Technology 40, 5312–5318) and the emission inferred from field observations (e.g., Jaffe, D., Prestbo, E., Swartzendruber, P., Weiss-Penzias, P., Kato, S., Takami, A., Hatakeyama, S., Kajii, Y., 2005. Export of atmospheric mercury from Asia. Atmospheric Environment 39, 3029–3038; Weiss-Penzias, P., Jaffe, D., Swartzendruber, P., Hafner, W., Chand, D., Prestbo, E., 2007. Quantifying Asian and biomass burning sources of mercury using the Hg/CO ratio in pollution plumes observed at the Mount Bachelor observatory. Atmospheric Environment 41, 4366–4379) in the region.

Semivolatile Fluorinated Organic Compounds in Asian and Western U.S. Air Masses

Semivolatile fluorinated organic compounds (FOCs) were measured in archived air sample extracts collected from Hedo Station Observatory (HSO) on Okinawa, Japan and Mount Bachelor Observatory (MBO), Oregon U.S. during the springs of 2004 (MBO and HSO) and 2006 (MBO). Fluorotelomer alcohols (FTOHs) were measured in both Asian and western U.S. air masses, though western U.S. air masses had significantly higher concentrations. Concentrations of fluorotelomer olefins in Asian air masses and 8:2 fluorotelomer acrylate in U.S. air masses were reported for the first time. N-ethyl perfluorooctane sulfonamide, N-methyl perfluorooctane sulfonamido ethanol, and N-ethyl perfluorooctane sulfonamido ethanol were also measured in Asian and western U.S. air masses but less frequently than FTOHs. The atmospheric sources and fate of FTOHs were investigated by estimating their atmospheric residence times, calculating FTOH concentration ratios, investigating FTOH correlations with nonfluorinated semivolatile organic compound concentrations, and determining air mass back trajectories. Estimated atmospheric residence times for 6:2 FTOH, 8:2 FTOH, and 10:2 FTOH were 50, 80, and 70 d, respectively, and the average concentration ratio of 6:2 FTOH to 8:2 FTOH to 10:2 FTOH at MBO in 2006 was 1.0 to 5.0 to 2.5. The relative order of these atmospheric residence times may explain the observed enhancement of 8:2 FTOH and 10:2 FTOH (relative to 6:2 FTOH) at MBO compared to North American indoor air (FTOH average ratio of 1.0 to 2.0 to 1.0). FTOH concentrations in western U.S. air masses were positively correlated (p < 0.05) with gas-phase polycyclic aromatic hydrocarbon and polychlorinated biphenyl concentrations and negatively correlated (p < 0.05) with agricultural pesticide concentrations. In comparison to western U.S. air masses, trans-Pacific air masses did not contain elevated concentrations of these compounds, whereas lower boundary layer air masses that passed over urban areas of the western U.S. did. This suggests that semivolatile FOCs are emitted from urban areas in the western U.S.

Influence of trans-Pacific pollution transport on acyl peroxy nitrate abundances and speciation at Mount Bachelor Observatory during INTEX-B

Abstract. We present month-long observations of speciated acyl peroxy nitrates (APNs), including PAN, PPN, MPAN, APAN, and the sum of PiBN and PnBN, measured at the Mount Bachelor Observatory (MBO) as part of the INTEX-B collaborative field campaign during spring 2006. APN abundances, measured by thermal dissociation-chemical ionization mass spectrometry (TD-CIMS), are discussed in terms of differing contributions from the boundary layer (BL) and the free troposphere (FT) and in the context of previous APN measurements in the NE Pacific region. PAN mixing ratios range from 11 to 3955 pptv, with a mean value of 334 pptv for the full measurement period. PPN is linearly correlated with PAN (r2=0.96), with an average abundance of 6.5% relative to PAN; other APNs are generally &lt;1% of PAN. Diurnal cycles and relationships of APNs with ozone reveal a gradient in hydrocarbon chemistry between the BL and the FT. On average, levels of APNs, ozone and PPN/PAN are substantially higher in FT air relative to BL air, suggesting that this site is strongly influenced by distant pollution sources. To estimate the impact of long-range transport of Asian pollution on atmospheric composition at MBO, we perform a detailed analysis utilizing HYSPLIT back trajectories. This analysis suggests that trans-Pacific transport of Asian pollution leads to substantial increases in APN and ozone mixing ratios at MBO, especially when transport occurs via the free troposphere. The ensemble of trajectories indicate that Asian-influenced free tropospheric air was sampled in ~16% of our data and contained a median PAN mixing ratio double that of the full dataset.

Quantifying Asian and biomass burning sources of mercury using the Hg/CO ratio in pollution plumes observed at the Mount Bachelor observatory

Total airborne mercury (TAM) and carbon monoxide (CO) were measured in 22 pollution transport “events” at Mt. Bachelor Observatory (MBO), USA (2.8 km asl) between March 2004 and September 2005. Submicron particulate scattering ( σ sp ) , ozone ( O 3 ) , and nitrogen oxides ( NO y ) were also measured and enhancement ratios for each chemical and aerosol species with CO were calculated. Events were categorized based on their source regions, which were determined by a combination of back trajectories, satellite fire detections, chemical and aerosol enhancement ratios, and meteorology. The mean Δ TAM / Δ CO values for each source region are: East Asian industrial ( 0.0046 ± 0.0013 ng m - 3 ppbv - 1 , n = 10 events, 236 h), Pacific Northwest U.S. (PNW) biomass burning ( 0.0013 ± 0.008 ng m - 3 ppbv - 1 , n = 7 events, 173 h), and Alaska biomass burning ( 0.0014 ± 0.0006 ng m - 3 ppbv - 1 , n = 3 events, 96 h). The Δ TAM / Δ CO means from Asian long-range transport (ALRT) and biomass burning events are combined with previous estimates of CO emissions from Chinese anthropogenic, global biomass burning, and global boreal biomass sources in order to estimate the emissions of gaseous elemental mercury (GEM) from these sources. The GEM emissions that we calculate here are: Chinese anthropogenic ( 620 ± 180 t y - 1 ), global biomass burning ( 670 ± 330 t y - 1 ) , and global boreal biomass burning ( 168 ± 75 t y - 1 ) , with errors estimated from propagating the uncertainty in the mean enhancement ratios and CO emissions. A comparison of our results with published mercury (Hg) emissions inventories reveals that the Chinese GEM emissions from this study are higher by about a factor of two, while our estimate for global biomass burning is consistent with previous studies.

Observations of reactive gaseous mercury in the free troposphere at the Mount Bachelor Observatory

We measured gaseous elemental mercury (GEM), particulate mercury (PHg), and reactive gaseous mercury (RGM), along with CO, ozone, and aerosol scatter at the Mount Bachelor Observatory (2.7 km above sea level), Oregon, from May to August 2005. The mean mercury concentrations (at standard conditions) were 1.54 ng/m3 (GEM), 5.2 pg/m3 (PHg), and 43 pg/m3 (RGM). RGM enhancements, up to 600 pg/m3, occurred at night and were linked to a diurnal pattern of upslope and downslope flows that mixed in boundary layer air during the day and free tropospheric air at night. During the night, RGM was inversely correlated (P &lt; 0.0001) with CO (r = −0.36), GEM (r = −0.73), and H2O (r = −0.44), was positively correlated with ozone (r = 0.38), and could not be linked to recent anthropogenic emissions from local sources or long‐range transport. Principal component analysis and a composite of change in RGM versus change in GEM during RGM enhancements indicate that a nearly quantitative shift in speciation is associated with increases in ozone and decreases in water vapor and CO. This argues that high concentrations of RGM are present in the free troposphere because of in situ oxidation of GEM to RGM. A global chemical transport model reproduces the RGM mean and diurnal pattern but underestimates the magnitude of the largest observed enhancements. Since the only modeled, in situ RGM production mechanisms are oxidation of GEM by ozone and OH, this implies that there are faster reaction rates or additional RGM production mechanisms in the free troposphere.