J. P. Greenberg

Ozone precursor relationships in the ambient atmosphere

The concentrations of ozone, nitrogen oxides, and nonmethane hydrocarbons measured near the surface in a variety of urban, suburban, rural, and remote locations are analyzed and compared in order to elucidate the relationships between ozone, its photochemical precursors, and the sources of these precursors. While a large gradient is found among remote, rural, and urban/suburban nitrogen oxide concentrations, the total hydrocarbon reactivity in all continental locations is found to be comparable. Apportionment of the observed hydrocarbon species to mobile and stationary anthropogenic sources and biogenic sources suggests that present-day emission inventories for the United States underestimate the size of mobile emissions. The analysis also suggests a significant role for biogenic hydrocarbon emissions in many urban/suburban locations and a dominant role for these sources in rural areas of the eastern United States. As one moves from remote locations to rural locations and then from rural to urban/suburban locations, ozone and nitrogen oxide concentrations tend to increase in a consistent manner while total hydrocarbon reactivity does not.

Thunderstorms: An Important Mechanism in the Transport of Air Pollutants

Acid deposition and photochemical smog are urban air pollution problems, and they remain localized as long as the sulfur, nitrogen, and hydrocarbon pollutants are confined to the lower troposphere (below about 1-kilometer altitude) where they are short-lived. If, however, the contaminants are rapidly transported to the upper troposphere, then their atmospheric residence times grow and their range of influence expands dramatically. Although this vertical transport ameliorates some of the effects of acid rain by diluting atmospheric acids, it exacerbates global tropospheric ozone production by redistributing the necessary nitrogen catalysts. Results of recent computer simulations suggest that thunderstorms are one means of rapid vertical transport. To test this hypothesis, several research aircraft near a midwestern thunderstrom measured carbon monoxide, hydrocarbons, ozone, and reactive nitrogen compounds. Their concentrations were much greater in the outflow region of the storm, up to 11 kilometers in altitude, than in surrounding air. Trace gas measurements can thus be used to track the motion of air in and around a cloud. Thunderstorms may transform local air pollution problems into regional or global atmospheric chemistry problems.

Emission of 2‐methyl‐3‐buten‐2‐ol by pines: A potentially large natural source of reactive carbon to the atmosphere

High rates of emission of 2-methyl-3-buten-2-ol (MBO) were measured from needles of several pine species. Emissions of MBO in the light were 1 to 2 orders of magnitude higher than emissions of monoterpenes and, in contrast to monoterpene emissions from pines, were absent in the dark. MBO emissions were strongly dependent on incident light, behaving similarly to net photosynthesis. Emission rates of MBO increased exponentially with temperature up to approximately 35°C. Above approximately 42°C, emission rates declined rapidly. Emissions could be modeled using existing algorithms for isoprene emission. We propose that emissions of MBO from lodgepole and ponderosa pine are the primary source of high concentrations of this compound, averaging 1–3 ppbv, found in ambient air samples collected in Colorado at an isolated mountain site approximately 3050 m above sea level. Subsequent field studies in a ponderosa pine plantation in California confirmed high MBO emissions, which averaged 25 μg C g−1 h−1 for 1-year-old needles, corrected to 30°C and photon flux of 1000 μmol m−2 s−1. A total of 34 pine species growing at Eddy Arboretum in Placerville, California, were investigated, of which 11 exhibited high emissions of MBO (>5 μg C g−1 h−1), and 6 emitted small but detectable amounts. All the emitting species are of North American origin, and most are restricted to western North America. These results indicate that MBO emissions from pines may constitute a significant source of reactive carbon and a significant source of acetone, to the atmosphere, particularly in the western United States.

The tropical forest and fire emissions experiment: Emission, chemistry, and transport of biogenic volatile organic compounds in the lower atmosphere over Amazonia

(7.8 ± 2.3 mg/m 2 /h) and monoterpene fluxes (1.2 ± 0.5 mg/m 2 /h) compared well between ground and airborne measurements and are higher than fluxes estimated in this region during other seasons. The biogenic emission model, Model of Emissions of Gases and Aerosols from Nature (MEGAN), estimates fluxes that are within the model and measurement uncertainty and can describe the large observed variations associated with land-use change in the region north-west of Manaus. Isoprene and monoterpenes accounted for � 75% of the total OH reactivity in this region and are important volatile organic compounds (VOCs) for modeling atmospheric chemistry in Amazonia. The presence of fair weather clouds (cumulus humilis) had an important impact on the vertical distribution and chemistry of VOCs through the planetary boundary layer (PBL), the cloud layer, and the free troposphere (FT). Entrainment velocities between 10:00 and 11:30 local time (LT) are calculated to be on the order of 8–10 cm/s. The ratio of methyl-vinyl-ketone (MVK) and methacrolein (MAC) (unique oxidation products of isoprene chemistry) with respect to isoprene showed a pronounced increase in the cloud layer due to entrainment and an increased oxidative capacity in broken cloud decks. A decrease of the ratio in the lower free troposphere suggests cloud venting through activated clouds. OH modeled in the planetary boundary layer using a photochemical box model is much lower than OH calculated from a mixed layer budget approach. An ambient reactive sesquiterpene mixing ratio of 1% of isoprene would be sufficient to explain most of this discrepancy. Increased OH production due to increased photolysis in the cloud layer balances the low OH values modeled for the planetary boundary layer. The intensity of segregation (Is) of isoprene and OH, defined as a relative reduction of the reaction rate constant due to incomplete mixing, is found to be significant: up to 39 ± 7% in the � 800-m-deep cloud layer. The effective reaction rate between isoprene and OH can therefore vary significantly in certain parts of the lower atmosphere.

Isoprene and monoterpene fluxes measured above Amazonian rainforest and their dependence on light and temperature

PUBLICATIONS Geophysical Research Letters RESEARCH LETTER 10.1002/2014GL062573 Key Points: • Mixing ratios of 12 Amazon monoterpenes reflect vertical forest structure • Light-dependent reactive monoterpene leaf emissions observed in ambient air • Monoterpene ozonolysis rates suggest important local aerosol precursor source Supporting Information: • Readme • Figure S1 • Figure S2 • Figure S3 • Figure S4 • Text S1 Correspondence to: A. B. Jardine, angela.jardine@inpa.gov.br Citation: Jardine, A. B., K. J. Jardine, J. D. Fuentes, S. T. Martin, G. Martins, F. Durgante, V. Carneiro, N. Higuchi, A. O. Manzi, and J. Q. Chambers (2015), Highly reactive light-dependent monoterpenes in the Amazon, Geophys. Res. Lett., 42, 1576–1583, doi:10.1002/2014GL062573. Received 19 NOV 2014 Accepted 1 FEB 2015 Accepted article online 4 FEB 2015 Published online 6 MAR 2015 Corrected 13 APR 2015 This article was corrected on 13 APR 2015. See the end of the full text for details. Highly reactive light-dependent monoterpenes in the Amazon A. B. Jardine 1 , K. J. Jardine 2 , J. D. Fuentes 3 , S. T. Martin 4 , G. Martins 1 , F. Durgante 1 , V. Carneiro 1 , N. Higuchi 1 , A. O. Manzi 1 , and J. Q. Chambers 2,5 Climate and Environment Department, Instituto Nacional de Pesquisas da Amazonia, Manaus, Brazil, 2 Climate Science Department, Earth Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA, 3 Department of Meteorology, College of Earth and Mineral Sciences, Pennsylvania State University, University Park, Pennsylvania, USA, School of Engineering and Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA, 5 Department of Geography, University of California, Berkeley, California, USA Abstract Despite orders of magnitude difference in atmospheric reactivity and great diversity in biological functioning, little is known about monoterpene speciation in tropical forests. Here we report vertically resolved ambient air mixing ratios for 12 monoterpenes in a central Amazon rainforest including observations of the highly reactive cis-β-ocimene (160 ppt), trans-β-ocimene (79 ppt), and terpinolene (32 ppt) which accounted for an estimated 21% of total monoterpene composition yet 55% of the upper canopy monoterpene ozonolysis rate. All 12 monoterpenes showed a mixing ratio peak in the upper canopy, with three demonstrating subcanopy peaks in 7 of 11 profiles. Leaf level emissions of highly reactive monoterpenes accounted for up to 1.9% of photosynthesis confirming light-dependent emissions across several Amazon tree genera. These results suggest that highly reactive monoterpenes play important antioxidant roles during photosynthesis in plants and serve as near-canopy sources of secondary organic aerosol precursors through atmospheric photooxidation via ozonolysis. 1. Introduction Many tree species produce monoterpenes (C 10 H 16 ), a diverse class of volatile terpenoids, which can be emitted into the atmosphere at high rates [Kesselmeier and Staudt, 1999; Fuentes et al., 2000]. Within ecosystems, monoterpenes mediate plant-microbe [Dorman and Deans, 2000] and plant-insect [Beyaert and Hilker, 2014] interactions and protect photosynthesis during abiotic stress [Penuelas and Llusia, 2002; Vickers et al., 2009]. Fueled by large total monoterpene emissions from forested ecosystems [Karl et al., 2002, 2003, 2004], atmospheric photochemical oxidation of monoterpenes generates low-volatility oxidation products that can partition to the particle phase [Yu et al., 1999; Fuentes et al., 2000; Kurpius and Goldstein, 2003; Mcfrederick et al., 2008; Martin et al., 2010]. These oxidation products, along with the oxidation products of isoprene (C 5 H 8 ), sesquiterpenes (C 15 H 24 ), and possibly higher-order terpenoids (C 20 H 32 and above), play important roles in the formation and growth of secondary organic aerosol (SOA) particles that can activate into cloud condensation nuclei [Claeys et al., 2004; Poschl et al., 2010]. Monoterpene ozonolysis reactions are important for SOA formation [Presto et al., 2005; Zhao et al., 2014] and postnucleation growth processes [Presto et al., 2005; Hao et al., 2009]. Further, the studies of Goldstein et al. [2004] and Fares et al. [2010] demonstrated that O 3 fluxes above a ponderosa pine forest (Pinus ponderosa) were dominated by gas phase chemistry, and their results suggested highly reactive monoterpenes likely contributing to a “missing” within-canopy O 3 sink. Thus, characterization of speciated monoterpenes and their associated ozonolysis reactions in the atmosphere is important for a comprehensive understanding of SOA sources [Chen et al., 2009]. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distri- bution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. JARDINE ET AL. Little is known about monoterpene composition in the tropics—a widely recognized major global source of terpenoids to the atmosphere [Guenther et al., 1995]. To date, only a few field observations targeting plant and atmospheric monoterpenes have been reported from the Amazon. Ambient levels of monoterpenes including α-pinene, β-pinene, and p-cymene have been reported [Helmig et al., 1998; Rinne et al., 2002; Kuhn et al., 2007] as well as low levels of highly reactive monoterpenes including myrcene, terpinolene, α-phellandrene and α-terpinene [Kesselmeier et al., 2000]. Other atmospheric monoterpene studies in the Amazon used the online technique of proton transfer reaction-mass spectrometry (PTR-MS), ©2015. The Authors.

Seasonal temperature variations influence isoprene emission

Isoprene (2-methyl-1,3-butadiene) emission from plants is highly temperature dependent. The influence of long-term variations in growth temperature on isoprene emission rates from bur oak (Quercus macrocarpa) leaves was investigated under controlled environmental conditions. Trees were installed in a growth chamber and exposed to a series of daytime temperatures that were varied after a period of 3–6 weeks. Emission capacity (measured at leaf temperature of 25°C and photosynthetic photon flux density of 900 µmol m−2 s−1) doubled when growth temperature was increased from 25 to 30°C. Ten days after the growth temperature was decreased to 20°C, isoprene emission capacity fell to 25 to 50% of its peak value. When growth temperature was returned to 30°C, emission capacity doubled within 5 hours and continued to increase over several days. The observed behavior can be described by modifying existing algorithms.

Carbon trace gas fluxes along a successional gradient in the Hudson Bay lowland

Patterns and controls of carbon trace gas emissions from wetlands may vary depending upon the spatial and temporal scale being examined. The factors affecting these emissions are thought to be hierarchically related according to their respective scales of importance. A hierarchical model of processes controlling methane emissions from wetlands is presented and examined here. During the 1990 Northern Wetlands Study (NOWES) methane (CH4), carbon dioxide (CO2), and non-methane hydrocarbon (NMHC) fluxes were measured in static chambers along a 100 km transect in the Hudson Bay lowland (HBL). Environmental variables, vegetation abundance, and ecosystem age and structure were also quantified at each sampling site. The findings indicate that CH4 emissions from peatlands (e.g., bogs and fens) and other wetlands (e.g., salt marshes) in the region were low, and were nil or negative (i.e., CH4 uptake) in forests and bog forests dominated by aspen and black spruce. Site to site variations in mean CH4 flux appeared to be most closely related to mean water table and sedge productivity, both of which are intercorrelated. Seasonal changes in CH4 flux tend to follow soil temperature fluctuations. Instantaneous CO2 and CH4 daytime fluxes exhibit a negative correlation, suggesting that photosynthetic assimilation of carbon may be related to CH4 emissions, although the processes of CO2 and CH4 production are occurring at somewhat different temporal scales. No diurnal variations in CH4 flux could be detected. While soil water pH trends are not fully explored, there is some indication that high CH4 fluxes are concentrated around pH 4 and pH 7. Soil temperature closely follows the seasonal progression of CH4 flux. Estimated CH4 seasonal flux (1.5–3.9 g CH4 m−2 season−1) and estimated aboveground net primary productivity (NPP) (90–400 g dry weight m−2 season−1) show systematic changes along a successional sequence which are consistent with patterns predicted from successional theory. Estimated seasonal NMHC emissions (0.5–1.4 g C m−2 season−1) exhibit an increase along the succession from salt marsh to Sphagnum bog communities. Data from several studies were combined to estimate seasonal CO2 flux from three sites. The estimated fluxes range from a net uptake of 23 g CO2 m−2 season−1 to a net loss of 77 g CO2 m−2 season−1, although there are large uncertainties in these estimates. It is inferred from the assessment of ecosystem age and structure that disturbance effects and successional changes occurring over hundreds to thousands of years in the HBL strongly control regional CH4, CO2 and NMHC emissions by influencing NPP, species composition, community structure, soil (peat) development, and landscape hydrology. Given this, it is likely that models of carbon trace gas flux based on succession models may be useful in predicting climate change-landscape change feedbacks.

Ozone observations and a model of marine boundary layer photochemistry during SAGA 3

A major purpose of the third joint Soviet-American Gases and Aerosols (SAGA 3) oceanographic cruise was to examine remote tropical marine O3 and photochemical cycles in detail. On leg 1, which took place between Hilo, Hawaii, and Pago-Pago, American Samoa, in February and March 1990, shipboard measurements were made of O3, CO, CH4, nonmethane hydrocarbons (NMHC), NO, dimethyl sulfide (DMS), H2S, H2O2, organic peroxides, and total column O3. Postcruise analysis was performed for alkyl nitrates and a second set of nonmethane hydrocarbons. A latitudinal gradient in O3 was observed on SAGA 3, with O3 north of the intertropical convergence zone (ITCZ) at 15–20 parts per billion by volume (ppbv) and less than 12 ppbv south of the ITCZ but never ≤3 ppbv as observed on some previous equatorial Pacific cruises (Piotrowicz et al., 1986; Johnson et al., 1990). Total column O3 (230–250 Dobson units (DU)) measured from the Akademik Korolev was within 8% of the corresponding total ozone mapping spectrometer (TOMS) satellite observations and confirmed the equatorial Pacific as a low O3 region. In terms of number of constituents measured, SAGA 3 may be the most photochemically complete at-sea experiment to date. A one-dimensional photochemical model gives a self-consistent picture of O3-NO-CO-hydrocarbon interactions taking place during SAGA 3. At typical equatorial conditions, mean O3 is 10 ppbv with a 10–15% diurnal variation and maximum near sunrise. Measurements of O3, CO, CH4, NMHC, and H2O constrain model-calculated OH to 9 × 105 cm−3 for 10 ppbv O3 at the equator. For DMS (300–400 parts per trillion by volume (pptv)) this OH abundance requires a sea-to-air flux of 6–8 × 109 cm−2 s−1, which is within the uncertainty range of the flux deduced from SAGA 3 measurements of DMS in seawater (Bates et al., this issue). The concentrations of alkyl nitrates on SAGA 3 (5–15 pptv total alkyl nitrates) were up to 6 times higher than expected from currently accepted kinetics, suggesting a largely continental source for these species. However, maxima in isopropyl nitrate and bromoform near the equator (Atlas et al., this issue) as well as for nitric oxide (Torres and Thompson, this issue) may signify photochemical and biological sources of these species.

Atmospheric volatile organic compounds (VOC) at a remote tropical forest site in central Amazonia

According to recent assessments, tropical woodlands contribute about half of all global natural non-methane volatile organic compound (VOC) emissions. Large uncertainties exist especially about fluxes of compounds other than isoprene and monoterpenes. During the Large-Scale Biosphere/Atmosphere Experiment in Amazonia - Cooperative LBA Airborne Regional Experiment 1998 (LBA-CLAIRE-98) campaign, we measured the atmospheric mixing ratios of different species of VOC at a ground station at Balbina, Amazonia. The station was located 100 km north of Manaus, SE of the Balbina reservoir, with 200-1000 km of pristine forest in the prevailing wind directions. Sampling methods included DNPH-coated cartridges for carbonyls and cartridges filled with graphitic carbons of different surface characteristics for other VOCs. The most prominent VOC species present in air were formaldehyde and isoprene, each up to several ppb. Concentrations of methylvinyl ketone as well as methacroleine, both oxidation products of isoprene, were relatively low, indicating a very low oxidation capacity in the lower atmospheric boundary layer, which is in agreement with a daily ozone maximum of <20 ppb. Total monoterpene concentration was below 1 ppb. We detected only very low amounts of VOC species, such as benzene, deriving exclusively from anthropogenic sources.

Biogenic hydrocarbon emissions from southern African savannas

Biogenic nonmethane hydrocarbon (NMHC) emissions were investigated at two field sites in the Republic of South Africa that include five important southern African savanna landscapes. Tropical savannas are a globally important biome with a high potential for biogenic emissions but no NMHC emission measurements in these regions or in any part of Africa have been reported. Landscape average hydrocarbon emissions were estimated by characterizing plant species composition and foliar density at each site, identifying and characterizing NMHC emissions of the most abundant plant species, and identifying and characterizing NMHC emissions of plant species with the highest NMHC emission rates. A hand-held portable analyzer proved to be a useful tool for identifying plants with high emission rates. A branch enclosure system, with gas chromatography and flame ionization detector, was used to quantify isoprene and monoterpene emission rates. Emission rates were species-specific and several genera had both high and low emitters. At least some species with high emission rates were identified in most savanna types. High and low emitters were found on both nutrient-rich and nutrient-poor soils. Landscape average emission capacities for the five savanna types range from 0.6 to 9 mg C m-2 h-1 for isoprene and about 0.05 to 3 mg C m-2 h-1 for monoterpenes. The savanna emission rates predicted by existing global models are within the range estimated for these five savanna types.