Effect of Bark Beetle Infestation on Secondary Organic Aerosol

Apr 30, 2012 - A. Gannet Hallar,. ‡ and Kara E. Huff Hartz. †,*. †. Southern Illinois University Carbondale, Carbondale, Illinois, USA. ‡. Des...
0 downloads 0 Views 948KB Size
Download PDF
Article pubs.acs.org/est

Effect of Bark Beetle Infestation on Secondary Organic Aerosol Precursor Emissions Hardik Amin,† P. Tyson Atkins,‡ Rachel S. Russo,§,⊥ Aaron W. Brown,† Barkley Sive,⊥,# A. Gannet Hallar,‡ and Kara E. Huff Hartz†,* †

Southern Illinois University Carbondale, Carbondale, Illinois, USA Desert Research Institute, Storm Peak Laboratory, Steamboat Springs, Colrrado, USA § Climate Change Research Center, University of New Hampshire, Durham, New Hampshire, USA ⊥ Department of Chemistry, Appalachian State University, Boone, North Carolina, USA # Environmental Sciences Program, Appalachian State University, Boone, North Carolina, USA ‡

S Supporting Information *

ABSTRACT: Bark beetles are a potentially destructive force in forest ecosystems; however, it is not known how insect attacks affect the atmosphere. The emissions of volatile organic compounds (VOCs) were sampled i.) from bark beetle infested and healthy lodgepole pine (Pinus contorta var. latifolia) trees and ii.) from sites with and without active mountain pine beetle infestation. The emissions from the trunk and the canopy were collected via sorbent traps. After collection, the sorbent traps were extracted with hexane, and the extracts were separated and detected using gas chromatography/mass spectroscopy. Canister samples were also collected and analyzed by a multicolumn gas chromatographic system. The samples from bark beetle infested lodgepole pine trees suggest a 5- to 20-fold enhancement in total VOCs emissions. Furthermore, increases in the βphellandrene emissions correlated with bark beetle infestation. A shift in the type and the quantity of VOC emissions can be used to identify bark beetle infestation but, more importantly, can lead to increases in secondary organic aerosol from these forests as potent SOA precursors are produced.

■

INTRODUCTION Atmospheric aerosols can impact climate through direct and indirect forcing, can degrade air quality and visibility, and can have detrimental effects on human health.1,2 Evidence indicates that emission of biogenic volatile organic compounds (BVOCs) provide a major source pathway for the formation of secondary organic aerosol (SOA).3−5 More recently, Liao et al.6 estimated that the BVOC emissions are four times larger than the anthropogenic volatile organic compound (AVOC) emissions in the United States. Globally, Tsigaridis and Kanakidou7 suggested that BVOCs dominate AVOCs in the production of SOA. Thus, to understand the impact of aerosols on climate, health, and atmospheric chemical processing, aerosol formation pathways, specifically via BVOC production mechanisms, must be known.8 Furthermore, with the potential impact of climate change (i.e., increased insect infestation), understanding the future emissions changes of BVOC will become increasingly important. BVOCs can be divided into three primary classes: isoprene (C 5 H 8 ), monoterpenes (C 10 H 16 ), and sesquiterpenes (C15H24).9 In regions dominated by coniferous (i.e., nonisoprene emitting) tree species, monoterpenes dominate the BVOC emissions.10 Overall, coniferous trees are responsible for approximately 10% of global monoterpene emissions.11 Specifically, lodgepole pine tree (Pinus contorta) emissions are dominated by three monoterpenes: α-pinene, β-pinene, and limonene.10 © 2012 American Chemical Society

The production of monoterpenes takes place within the plastids, the site of photosynthesis within a plant. Specifically in conifers, monoterpene synthesis occurs within specialized cells in the needles and resin canals of the bark.12 Monoterpenes represent the main fraction of essential oils that are produced and stored in plant secretory organs like resin ducts.13 As a result of this storage mechanism, the tree exhibits a large storage pool of monoterpenes compared to the emission rates.14 Hence, the emission of monoterpenes via volatilization out of storage organs is related to the vapor pressure and to the transport resistance along the diffusion path.13 Increases in monoterpene emissions are also a long-term plant defense mechanism against herbivore attacks. For example, previous results showed that weevil (Strophosoma melanogrammum) attacks on spruce trees in Denmark had a significant effect on local monoterpene emissions. In fact, a single weevil induced a 3-fold increase in monoterpene emissions and the response lasted for several weeks.12 Furthermore, large pine weevil (Hylobius abiettis) feedings on Scots pine seedlings (Pinus sylvestris) induced a nearly 3-fold increase in monoterpene emissions.15 Received: Revised: Accepted: Published: 5696

November 23, 2011 March 27, 2012 April 30, 2012 April 30, 2012 dx.doi.org/10.1021/es204205m | Environ. Sci. Technol. 2012, 46, 5696−5703

Environmental Science & Technology

Article

1 were logged mid-September during the campaign. After logging, a third site (site 3) was selected, and it is located at site 1. Site 1 and site 3 are 3.6 km west of SPL, and site 2 is 2.3 km west of SPL. Three trees were selected for sampling at each site (Table 1). At each site an infested tree and one or two healthy

Across Western North America, there is currently a sudden large-scale population increase in mountain pine beetles (Dendroctonus ponderosae). The lodgepole pines (Pinus contorta var. latifolia) are the primary host for these beetles.16 Essentially, female beetles select a tree and bore through the bark into the phloem. While boring into the tree, the beetle processes the host monoterpenes into pheromones to attract male beetles.17 The male then helps clear out the entrance gallery.18 Simultaneously, the beetle severs the pine tree’s resin canals, and resin flows into the wound to slow down the beetle. This resin contains monoterpenes, which are toxic to the beetle but not at the concentration encountered in the resin.19 If the beetle proceeds through the resin, the female beetle then lays eggs in ovipositional galleries under the bark.20 These beetles also transport fungi that assist in killing the tree. The resulting larvae develop by feeding on the phloem and fungi.18 The pine tree responds to the beetle−fungal attack with a broad chemical defense including increases in monoterpenes.17 Miller et al.21 inoculated lodgepole pine stands with a mountain pine beetle in the Colville National Forest and repeated these experiments in the St. Joe National Forest. They found a 4-fold increase of monoterpenes in the phloem tissue surrounding the inoculation site over the course of three days. In a similar study, Raffa and Berryman22 investigated the chemical change in the phloem of lodgepole pines when attacked by mountain pine beetles and its symbiotic fungus, Europhium clavigerum. In this study, all trees were inoculated, and as a result, an increase was observed in the monoterpene output. The response was rapid (i.e., within three days of inoculations), and the response appeared localized near the infection point. The current mountain pine beetle outbreak has resulted in wide-scale tree mortality. For example, the current beetle epidemic in British Columbia, Canada, is an order of magnitude larger than all previously recorded outbreaks.23,24 The infestation has increased in area from 164 000 ha in 1999 to more than 11 million ha in 2007.25 One reason for this outbreak is changes in winter and summer temperatures and reduced summer precipitation in recent decades. Climate change has allowed for the outbreak to expand northward and into higher elevation forests.24,26,27 This article addresses the atmospheric impact of the mountain pine beetle epidemic. This work specifically focuses on monoterpene emissions that have the greatest potential in SOA formation and addresses the impact of the mountain pine bark beetle epidemic on SOA.

Table 1. Location and Description of Sampled Trees description site 1 healthy lodgepole pine, recovered from prior infestation, old pitch tubes present infested lodgepole pine healthy lodgepole pine, sprayed with carbaryl site 2 infested lodgepole pine healthy lodgepole pine deceased lodgepole pine, old pitch tubes present indicating prior infestation site 3 healthy lodgepole pine, recovered from prior infestation, old pitch tubes present infested lodgepole pine healthy lodgepole pine, recovered from prior attack, old pitch tubes present, and sprayed with carbaryl

abbreviationa

number of sorbent trap samples collected from trunk,canopy

S1T1

15,15

S1T2 S1T3

18,15 15,15

S2T6 S2T7 S2T8

37,34 37,37 19,19

S3T9

18,15

S3T10 S3T11

18,0 18,18

a

Tree numbers 4 and 5 were Engelmann spruce and thus not included in this study.

trees without current infestation were selected. At site 1 and site 3, some of the healthy trees had old pitch tubes (resin deposits on the trunk indicating prior beetle infestation), and some of the healthy trees that were previously attacked by bark beetles and sprayed with carbaryl, a beetle insecticide. At site 2, a deceased tree with pitch tubes was also selected for sampling. Sorbent Trap Collection and Analysis. Gas samples were collected at the trunk and canopy by dynamic sampling. This method was adapted from the work of Raguso and Pellmyr30 and the procedure is described below. Sorbent traps were prepared by placing 110 mg of Porapak Q sorbent (80/100 mesh, Grace Davidson) between two 3 mm plugs of deactivated borosilicate glass wool (Restek) at the neck of a 53/4” glass Pasteur pipet (Fisher Scientific). The trap was rinsed with 5−6 volumes using n-hexane (GC Resolv, Fisher). The traps were air-dried and then wrapped using prefired aluminum foil. For sampling, a PAS-500 (Spectrex) micro air sampler was attached to each sorbent trap using 1/4” ID Tygon tubing 1 m in length. The flow rate of the PAS-500 was adjusted to 400 mL/min using a Gilibrator air flow calibrator, and the flow rate was checked frequently between sample collections. Samples were taken simultaneously at the trunk and canopy. For trunk sampling, the PAS-500, tubing, and trap were positioned so that the inlet of the trap was near (90 ng/L). Variations in the total VOC concentrations from biogenic emissions are expected in part because emissions vary with season, solar radiation, and temperature.11 To compare the total VOC concentrations found at each site, the samples were grouped according to the location of the sampling (trunk vs canopy) and the tree at each site. Figure 1 shows the

Table 3. Statistical Comparison of the Total VOCs Sampled p trunk healthy vs infested healthy pine with prior infestation vs infested pine (S1T1 vs S1T2) healthy pine, sprayed vs infested pine (S1T3 vs S1T2) healthy pine vs infested pine (S2T7 vs S2T6) healthy pine with prior infestation vs infested pine (S3T9 vs S3T10) healthy pine, sprayed vs infested pine (S3T11 vs S3T10) deceased vs healthy or infested deceased pine vs infested pine (S2T8 vs S2T6) deceased pine vs healthy pine (S2T8 vs S2T7)

Figure 1. Total VOC concentrations for all sorbent trap samples collected. The center line of the box is the median, the edges of the blocks are the 25th and 75th percentile, and the whiskers are the 10th and 90th percentile. The closed circles and open circles represent the average total VOCs sampled near the trunk and in the canopy, respectively. Trees labeled “I” on the x axis are beetle infested. Insert: scale expansion for total VOC concentrations for noninfested trees.

a

p canopy

4.4 × 10−5

0.62

2.9 × 10−5

0.54

0.018 0.022

0.996

0.011

a

0.016 0.14

0.0057 0.033

a

No canopy samples were collected at S3T10.

in order to reduce differences in VOC emissions resulting from inhomogeneities in temperature and solar radiation. There is a statistically significant difference (p = 0.022) between the total VOCs sampled from the trunks of healthy versus infested trees at the same site. However, the canopies of healthy and infested trees show no significant difference in the total VOC concentration sampled (p = 0.54). Gara et al.37 found that the total monoterpenes emitted per day increased by a factor of nearly five (from 6.8 μg m−2 day−1 to 32.38 μg m−2 day−1) from the trunks of pine trees (Pinus contorta murryana) with heartwood decay fungi present compared to trunks with no fungi present. In comparison, for this study at site 1, the total VOC concentrations increased by a factor of 21 (from 4.5 ng/L at a healthy tree to 94.2 ng/L at an infested tree). At site 2, the total VOC concentrations increased by a factor of 13 (from 5.4 ng/L at a healthy tree to 72.7 ng/L at an infested tree). At site 3, the total VOC concentrations increased by a factor of 3 (from 20.6 ng/L at a healthy tree to 60.9 ng/L at an infested tree). Although the heartwood decay fungi is not the same type of fungi associated with bark beetles, the observation of the increases in VOC emissions are consistent with the work of Gara et al.37 Samples were collected at site 2 from a deceased pine tree that was caused by beetle infestation, and the total VOC concentrations from this tree tended to be lower than the other samples at the same site. There was a significant difference between the average total VOC concentrations (Table 3) of the deceased and infested pine both at the trunk (p = 0.016) and the canopy (p = 0.0057). However, the differences between the total VOC concentrations of the deceased and healthy pine were lower, thus the probabilities that the average total VOC concentrations at the trunk (p = 0.14) and the canopy (p = 0.033) were higher indicating very little difference. The total VOC samples at the deceased tree could be affected by emissions from nearby infested and healthy trees. If the deceased tree only emits a negligible concentration of VOCs,

distribution of the total VOC concentration as a box and whiskers plot, where the center line of the box is the median, the edges of the blocks are the 25th and 75th percentile, the whiskers are the 10th and 90th percentile, and the average total VOCs sampled near the trunk and in the canopy is shown with closed and open circles, respectively. The concentrations of the total VOCs overlap with the exception of the samples collected at the trunks of infested trees (S1T2, S2T6, S3T10). The healthy site 3 trees tended to have higher total VOC concentrations than the other healthy trees. Logging at this site prior to sample collection could cause an increase to background VOC concentrations. Statistical tests were performed to compare samples from infested trees to samples from trees that were not infested. For each test, an independent, two-sample t test was performed, and the null hypothesis tested was that the averages were the same. The result of the t test is the probability (p) that the averages of the populations are equal. A low p-value indicates that it is unlikely that the average total VOC concentrations of the infested trees and noninfested trees are the same. Prior to each t test, an F-test was used to compare the standard deviations. When the F-test indicated the difference in standard deviation of the two populations was not significant at the 99% confidence level, the standard deviations were pooled. The total VOC concentrations from samples collected at the canopy and trunk at each tree are compared in Table 2. The average total VOCs from trunks of infested trees (S1T2, S2T6) are significantly greater than the average total VOCs from their canopy samples, (S1T2 p = 3.8 × 10−5 S2T6 p = 0.019). In contrast, there is no significant difference in the averages of canopy and trunk total VOC concentrations for healthy, dead, or healthy and recovered trees. This suggests that there is a correlation between active beetle infestation, which occurs in the trunk of the tree and an increase in total VOC emissions. The higher VOC concentrations found near the trunks of 5699

dx.doi.org/10.1021/es204205m | Environ. Sci. Technol. 2012, 46, 5696−5703

Environmental Science & Technology

Article

Table 4. Concentration ± Standard Error of the Meana (ng/L) of the Major VOCs, Averaged over the Entire Study α-pinene S1T1 trunk canopy S1T2 trunk canopy S1T3 trunk canopy S2T6 trunk canopy S2T7 trunk canopy S2T8 trunk canopy S3T9 trunk canopy S3T10 trunk canopyb S3T11 trunk canopy

1.4 1.1 4.4 1.5 5 0.21 8 2.6 2.2 2.7 0.3 nd 11 9 5.3 8 2.2

± ± ± ± ± ± ± ± ± ± ±

0.6 0.54 1.0 0.6 3 0.11 3 0.9 0.8 1.1 0.3

±3 ±3 ±2 ±3 ± 1.5

camphene 0.06 0.02 0.16 0.09 1.2 0.02 1.5 0.5 0.5 0.6 0.09 0.01 2.5 1.0 1.1 2.2 0.7

± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.03 0.02 0.05 0.04 0.7 0.01 0.7 0.2 0.2 0.3 0.09 0.01 0.7 0.4 0.4

± 0.9 ± 0.5

β-pinene 0.50 ± 0.03 ± 6.8 ± nd 0.5 ± 0.06 ± 4.2 ± 0.6 ± 0.5 ± 0.5 ± 0.18 ± 0.07 ± 1.1 ± 0.53 ± 4.7 ± 1.0 ± 0.4 ±

0.20 0.03 1.2 0.3 0.06 1.5 0.2 0.2 0.2 0.10 0.05 0.4 0.20 1.3

0.4

3-carene 0.24 0.08 8.4 0.15 1.5 1.0 13 0.9 0.4 0.8 0.06 0.24 4.2 5.4 5.0 2.4 1.7

± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.08 0.04 1.7 0.06 0.7 1.0 5 0.4 0.2 0.4 0.04 0.22 1.5 1.9 1.2

± 0.8 ± 1.0

β-phellandrene 2.3 1.4 69 1.7 0.8 0.8 43 1.2 1.5 1.0 1.4 0.04 0.9 0.8 43 0.7 0.21

± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.6 0.5 12 0.6 0.3 0.5 17 0.4 0.6 0.3 0.6 0.02 0.3 0.3 12

± 0.2 ± 0.17

γ-terpinene nd nd 0.14 nd 0.11 nd 0.5 0.05 0.02 0.07 nd nd 0.43 0.47 0.30 0.20 0.07

± 0.07 ± 0.07 ± ± ± ±

0.3 0.05 0.02 0.05

± 0.21 ± 0.18 ± 0.19 ± 0.08 ± 0.05

estragole nd nd 2.6 ± 0.4 nd nd nd 0.20 ± 0.09 nd nd nd nd nd nd nd 0.36 ± 0.07 nd nd

p-cymene 0.01 nd 0.38 nd 0.10 nd 0.20 0.06 0.04 0.06 0.35 0.05 0.09 0.17 0.22 0.15 0.03

± 0.01 ± 0.07 ± 0.04 ± ± ± ± ± ± ± ± ±

0.06 0.02 0.01 0.03 0.09 0.03 0.04 0.07 0.07

± 0.05 ± 0.03

a

Standard error of the mean was calculated by standard deviation divided by n1/2, where n is the number of samples given in Table 1. bNo canopy samples were collected at S3T10. nd = not detected.

nearby infested and healthy trees could cause an overestimation of the VOC emissions from the deceased tree, which leads to a less significant difference between deceased tree’s and healthy tree’s total VOC concentrations. Decomposition by fungi within the deceased tree could lead to additional VOC emissions, but these were not observed at this tree. VOC Speciation. Individual VOCs have different potentials to form aerosol because they have different oxidation kinetics and the oxidation products have different volatility distributions (i.e., aerosol yields). Thus, identification and quantification for the biogenic VOCs sampled near healthy and infested trees are needed to understand how changes in VOC types and concentrations will ultimately impact SOA levels. Table 4 lists the average concentration for the major VOCs sampled using sorbent traps near the trunk and canopy at each site. The dominant biogenic VOCs found in the samples were the following monoterpene isomers: α-pinene, β-pinene, 3-carene, and β-phellandrene, with average concentrations that ranged from less than 1 ng/L to greater than 50 ng/L. Other monoterpenes (tricyclene, camphene, sabinene, myrcene, γterpinene, and terpinolene), a monoterpene derivative (1,4cineole), and aromatic VOCs (estragole and p-cymene) were sometimes found in the samples at concentrations less than 2 ng/L (Table S4 of the Supporting Information). The chemical identities of the VOCs are generally consistent with the VOCs emissions from lodgepole pine trees.10 Because the total VOC concentration was higher for samples collected near the trunks of infested trees, the distributions of individual VOCs from the trunks of healthy and infested trees were compared. Figure 2 shows that the individual VOC sample concentrations were higher at the trunks of infested trees than healthy trees. Statistically significant increases (p < 0.001) were observed for β-pinene, 3-carene, β-phellandrene, estragole, and p-cymene. The β-phellandrene concentrations measured near infested pine trunks were more than thirty times higher than healthy pine trunks. In addition to the sorbent samples, whole air samples using canisters were collected. The average concentrations of the monoterpenes determined in the canister samples are listed in

Figure 2. Box and whisker plots of the major VOCs found in the sorbent trap samples collected from the trunks of healthy (S1T1, S2T7, S3T9) and infested trees (S1T2, S2T6, S3T10). The median, the 25th percentile, and the 75th percentile are denoted by the center line and the edges of the box, the 10th, and 90th percentiles are denoted by the whiskers, and the mean is denoted by the symbols.

Table 5 (the additional VOCs determined using the multicolumn separation system are listed in Table S5 of the Supporting Information). Seven of the eight monoterpenes that were present in the VOC canister samples were also present in the sorbent samples: α-pinene, camphene, β-pinene, 3-carene, β-phellandrene, γ-terpinene, and p-cymene. The Storm Peak, the site 2 noninfested tree (S2T7), and site 3 contained the lowest levels of monoterpenes and with no predominant species (more than 2:1). In contrast, the site 1 and site 2 infested tree (S2T6) samples contained higher concentrations of β-phellandrene, with intermediate concentrations of αpinene, β-pinene, 3-carene, and lower concentrations of camphene, p-cymene, and γ-terpinene. The pattern of monoterpenes is similar for the canister and sorbent trap samples. The canister analysis method was not optimized for estragole, so it was not detected. Limonene was also found in the VOC canister samples but not in the sorbent samples. Limonene and β-phellandrene were resolved on the OV-624 column used for VOC canister samples 5700

dx.doi.org/10.1021/es204205m | Environ. Sci. Technol. 2012, 46, 5696−5703

Environmental Science & Technology

Article

Table 5. Average Monoterpene Concentration±Standard Error of the Mean (ng/L) Collected via Canistersa site 1 S2T6 S2T7 site 3 Storm Peak a

α-pinene

camphene

β-pinene

3-carene

limonene

β-phellandrene

1.78 ± 0.53 0.9 ± 0.6 0.062 ± 0.016 0.047 ± 0.010 0.051 ± 0.02

0.37 ± 0.07 0.30 ± 0.14 0.080 ± 0.023 0.035 ± 0.006 0.033 ± 0.006

3.2 ± 0.7 1.0 ± 0.8 0.070 ± 0.011 0.062 ± 0.016 0.042 ± 0.012

2.9 ± 0.5 2.9 ± 2.4 0.043 ± 0.006 0.036 ± 0.008 0.018 ± 0.005

1.2 ± 0.2 0.50 ± 0.38 0.071 ± 0.021 0.054 ± 0.021 0.059 ± 0.020

8.0 ± 5.0 5.7 ± 5.2 0.015 ± 0.006 0.011 ± 0.004 0.0049 ± 0.0017

p-cymene

γ-terpinene

± ± ± ± ±

0.040 ± 0.016 0.15 ± 0.14 0.023 ± 0.006 0.0070 ± 0.0039 0.025 ± 0.018

0.73 0.37 0.15 0.11 0.14

0.21 0.26 0.03 0.01 0.08

Standard error of the mean was calculated by standard deviation divided by n1/2, where n = 3.

containing α-pinene, β-pinene, and 3-carene in healthy trees to a monoterpene mixture that is dominated by β-phellandrene in infested trees. These results suggest that SOA concentrations could increase from bark beetle infestation because the concentrations of SOA precursors increase. The magnitude of this increase is difficult to predict at this time because very few studies have addressed SOA from β-phellandrene possibly due to the lack of a high purity compound that is commercially available. β-phellandrene is a cyclic monoterpene and contains two carbon−carbon double bonds, one exo and one endo with respect to the ring. The oxidation kinetics of β-phellandrene with respect to OH (1.7 × 10−10 molec−1 cm3 s−1), O3 (4.7 × 10−17 molec−1 cm3 s−1), and NO3 (8.0 × 10−12 molec−1 cm3 s−1) are similar to the major monoterpenes emitted from noninfested trees, including: α-pinene (OH, 5.2 × 10−11 molec−1 cm3 s−1; O3, 8.4 × 10−17 molec−1 cm3 s−1; and NO3, 6.2 × 10−12 molec−1 cm3 s−1) and 3-carene (OH, 8.8 × 10−11 molec−1 cm3 s−1; O3, 3.7 × 10−17 molec−1 cm3 s−1; and NO3, 9.1 × 10−12 molec−1 cm3 s−1).40 Thus, we expect the oxidation kinetics of the VOCs emitted from infested trees that form SOA will have at least the same order of magnitude as the oxidation kinetics as healthy trees and, as a result, a change in the types of VOCs emitted will not inhibit SOA formation. A portion of the VOC oxidation products can condense to form SOA. The efficacy of VOCs to form SOA depends on the structure and concentration of VOC, the type and concentration of oxidant, and the environmental conditions (i.e., temperature, relative humidity). The results in this work suggest that upon bark beetle infestation, the concentration of total VOCs increase, and the dominant VOCs change from monoterpenes with one carbon−carbon double bond (αpinene, β-pinene, 3-carene) to β-phellandrene, which has two double bonds. The ratio of the SOA produced per VOC oxidized is termed the SOA yield, and VOCs with higher yields are more likely to produce higher amounts of SOA. Only one measure of SOA yield from β-phellandrene is available. Surratt et al.41 generated OH-initiated SOA from a β-phellandrene/ limonene mixture (in the presence of NOx) and using an acidic MgSO4/H2SO4 seed aerosol. The average SOA volume produced from ∼100 ppb of a 40/60 mixture of βphellandrene/limonene was 169 μm3/cm3. The average SOA volume produced from 86 ppb limonene under similar conditions was 186 μm3/cm3. SOA yields depend on NOx concentrations, and the sampling sites may have lower NOx concentrations than the NOx concentrations used by Surratt et al.41 If the SOA yields from individual monoterpenes are additive in a mixture, this indicates that the OH-initiated SOA yield from β-phellandrene is significant. The relative yield is slightly less than the yield from limonene under similar conditions but greater than α-pinene and β-pinene.41 Thus, we might expect the SOA yields to increase when bark beetle

analysis; however, the VF-5 ms column used for the separation of sorbent samples does not resolve limonene from βphellandrene. For sorbent samples, the difference between electron impact mass spectra of β-phellandrene and limonene was used: limonene’s dominant product ion is m/z 68, and βphellandrene does not form ion fragments with m/z 68 to a significant extent. Limonene could have been present in the sorbent samples, but the lack of m/z 68 in the mass spectra indicates that it was not detected. This suggests that the βphellandrene concentration is greater than the limonene concentration, which is consistent with the canister samples. The sum of the total monoterpenes found in the canister samples ranged from 0.4−18 ng/L and is roughly an order of magnitude lower than the range found in the sorbent samples. This was most likely a direct result of the difference in sampling methods. The sorbent samples have a longer sampling period (2 h) than the canister samples, which are essentially instantaneous samples (30−60 s). The longer sampling period may allow for the headspace to re-equilibrate with BVOC emissions, which could lead to higher measured concentrations. In addition to the significant difference in sampling times, the proximity to the individual tree sampled would also result in the differences in concentrations. However, regardless of the sampling method, the BVOC emissions increased when bark beetle infested trees were sampled, and the dominant BVOC was β-phellandrene for infested trees. The types and distributions of monoterpenes observed in healthy and infested samples are generally consistent with prior work. The major monoterpenes found by Rhoades38 emitted from the undamaged trunks of lodgepole pine trees were βphellandrene, β-pinene, α-pinene, p-cymene, and an unidentified oxygenated monoterpene. Similar monoterpenes were found by Gara et al.37 in lodgepole pine trunks infested with heartwood decay fungi: β-phellandrene, β-pinene, α-pinene, and p-cymene. Also, the types of VOCs and the observed increases are generally consistent with the work of Jost et al.,39 where the bark from lodgepole, hybrid, and jack pine trees were inoculated with three types of blue stain fungi, a symbiotic species associated with mountain pine beetle infestation. The gas emissions from bark samples that were inoculated with fungi contained eight monoterpenes (α-pinene, camphene, βpinene, sabinene, α-phellandrene, myrcene, limonene, βphellandrene) and p-cymene. Jost et al.39 observed speciesdependent increases and decreases in the relative monoterpene concentrations. For the lodgepole pine, camphene, limonene, and α-pinene emissions decreased whereas the β-phellandrene emissions increased with fungi inoculation. Potential Impact of Bark Beetle Infestation on SOA. The analysis of the sorbent trap and canister samples suggests that upon bark beetle infestation, lodgepole pine trees show increases in total VOC emissions and a shift in the types of VOCs emitted, that is, from a mixture of monoterpenes 5701

dx.doi.org/10.1021/es204205m | Environ. Sci. Technol. 2012, 46, 5696−5703

Environmental Science & Technology

Article

Geophys. Res. [Atmos.] 2007, 112 (D6), DO6201 DOI: 10.1029/ 2006JD007813. (7) Tsigaridis, K.; Kanakidou, M. Secondary organic aerosol importance in the future atmosphere. Atmos. Environ. 2007, 41, 4682−4692, DOI: 10.1016/j.atmosenv.2007.03.045. (8) Hallquist, M.; Wenger, J. C.; Baltensperger, U.; Rudich, Y.; Simpson, D.; Claeys, M.; Dommen, J.; Donahue, N. M.; George, C.; Goldstein, A. H.; Hamilton, J. F.; Herrmann, H.; Hoffmann, T.; Iinuma, Y.; Jang, M.; Jenkin, M. E.; Jimenez, J. L.; Kiendler-Scharr, A.; Maenhaut, W.; McFiggans, G.; Mentel, Th. F.; Monod, A.; Prévôt, A. S. H.; Seinfeld, J. H.; Surratt, J. D.; Szmigielski, R.; Wildt, J. The formation, properties and impact of secondary organic aerosol: current and emerging issues. Atmos. Chem. Phys. 2009, 9 (14), 4521−5388. (9) Sakulyanontvittaya, T.; Guenther, A.; Helmig, D.; Milford, J.; Wiedinmyer, C. Secondary organic aerosol from sesquiterpene and monoterpene emissions in the United States. Environ. Sci. Technol. 2008, 42 (23), 8784−8791, DOI: 10.1021/es800817r. (10) Geron, C.; Rasmussen, R.; Arnts, R. R.; Guenther, A. A review and synthesis of monoterpene speciation from forests in the United States. Atmos. Environ. 2000, 34 (11), 1761−1781, DOI: 10.1016/ S1352-2310(99)00364-7. (11) Guenther, A.; Hewitt, C. N.; Erickson, D.; Fall, R.; Geron, C.; Graedel, T.; Harley, P.; Klinger, L.; Lerdau, M.; McKay, W. A.; Pierce., T.; Scholes, B.; Steinbrecher, R.; Tallamraju, R.; Taylor, J.; Zimmerman, P. A global model of natural volatile organic compound emissions. J. Geophys. Res. [Atmos.] 1995, 100 (D5), 8873−8892, DOI: 10.1029/94JD02950. (12) Priemé, A.; Knudsen, T. B.; Glasius, M.; Christensen, S. Herbivory by the weevil, Strophosoma melanogrammum, causes several fold increase in emission of monoterpenes from young Norway spruce (Picea abies). Atmos. Environ. 2000, 34 (5), 711−718, DOI: 10.1016/ S1352-2310(99)00357-X. (13) Kesselmeier, J.; Staudt, M. Biogenic volatile organic compounds (VOC): An overview on emission, physiology and ecology. J. Atmos. Chem. 1999, 33 (1), 23−88, DOI: 10.1023/A:1006127516791. (14) Lerdau, M. T.; Dilts, S. B.; Westberg, H.; Lamb, B. K.; Allwine, E. J. Monoterpene emission from ponderosa pine. J. Geophys. Res. [Atmos.] 1994, 99 (D8), 16609−16615, DOI: 10.1029/94JD00406. (15) Heijari, J.; Blande, J. D.; Holopainen, J. K. Feeding of large pine weevil on Scots pine stem triggers localised bark and systemic shoot emission of volatile organic compounds. Environ. Exp. Bot., 2011, 71 (3), 390−398, DOI: 10.1016/j.envexpbot.2011.02.008. (16) Wood, S. L. A revision of bark beetle genus Dendroctonus erichson (Coleoptera: Scolytidae). Great Basin Nat. 1963, 23, 117. (17) Raffa, K. F. Induced defensive reactions in conifer-bark beetle systems. In Phytochemical Induction by Herbivores; Tallamy, D. W., Raupp, M. J., Eds.; Academic Press: New York, 1991; pp 245−276. (18) Raffa, K. F.; Aukema, B. H.; Erbilgin, N.; Klepzig, K. D.; Wallin, K. F. Interactions among conifer terpenoids and bark beetles across multiple levels of scale: An attempt to understand links between population patterns and physiological processes. In Recent Advances in Phytochemistry; Romeo, J., Ed. Elsevier: Amsterdam, 2005; Vol. 39, pp 80−118. (19) Smith, R. H. Toxicity of pine resin vapors to three species of Dendroctonus bark beetles. J. Econ. Entomol. 1963, 56 (6), 827−831. (20) Amman, G. D. Mountain pine beetle brood production in relation to thickness of lodgepole pine phloem. J. Econ. Entomol. 1972, 65 (1), 138−140. (21) Miller, R. H.; Berryman, A. A.; Ryan, C. A. Biotic elicitors of defense reactions in lodgepole pine. Phytochemistry 1986, 25 (3), 611− 612, DOI: 10.1016/0031-9422(86)88008-6. (22) Raffa, K. F.; Berryman, A. A. Physiological aspects of lodgepole pine wound responses to a fungal symbiont of the mountain pine beetle (Dendroctonus ponderosae) (Coleoptera: Scolytidae). Can. Ent. 1983, 115 (7), 723−734, DOI: 10.4039/Ent115723-7. (23) Taylor, S. W.; Carroll, A. L.; Alfaro, R. I.; Safranyik, L. Forest, Climate and Mountain Pine Beetle Outbreak Dynamics in Western Canada. In The Mountain Pine Beetle: A Synthesis of Biology,

infestations occur especially because we saw an overall increase in VOC concentration due to infestation. The total VOCs emitted from the trunks of bark beetle infested lodgepole pine trees were higher than the total VOCs emitted from the trunks of healthy, noninfested lodgepole pine trees. Because the dominant monoterpene, β-phellandrene, reacts with oxidants on an atmospherically relevant time scale and forms SOA with significant yields, higher SOA concentrations due to bark beetle infestation may occur. Thus, it is reasonable to assume that the bark beetle epidemic in the Western U.S. has led to higher monoterpene concentrations and higher SOA concentrations and yields, which impacts the background particulate matter concentrations, deleterious health effects due to increased particulate matter concentrations, and may impact radiative forcing in the atmosphere.

■

ASSOCIATED CONTENT

S Supporting Information *

Map of the sampling site, VOC concentrations for each sample, concentrations of minor VOCs, and C2−C6 alkanes, aromatics, haloalkanes, and alkyl nitrate concentrations from canister samples, details for canister sample analysis, and F-test results. This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: khuff[email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This material is based upon work supported by the National Science Foundation collaborative Grant No. 0939021; 0938940. We appreciate the advice and expertise of Dr. Craig Dodson with regard to sampling methodology and design. The authors appreciate the Steamboat Ski Resort for providing logistical support and in-kind donations towards this study. The DRI’s SPL is an equal opportunity service provider and employer and is a permitee of the Medicine-Bow Routt National Forests.

■

REFERENCES

(1) Charlson, R. J.; Schwartz, S. E.; Hales, J. M.; Cess, R. D.; Coakley, J. A.; Hansen, J. E.; Hoffman, D. J. Climate forcing by anthropogenic aerosols. Science 1992, 255, 423−430, DOI: 10.1126/science.255.5043.423. (2) Akimoto, H. Global air quality and pollution. Science 2003, 302, 1716−1719, DOI: 10.1126/science.1092666. (3) Hoffmann, T.; Odum, J. R.; Bowman, F.; Collins, D.; Klockow, D.; Flagan, R. C.; Seinfeld, J. H. Formation of organic aerosols from the oxidation of biogenic hydrocarbons. J. Atmos. Chem. 1997, 26 (2), 189−222, DOI: 10.1023/A:1005734301837. (4) Griffin, R. J.; Crocker, D. R.; Flagan, R. C.; Seinfeld, J. H. Organic aerosol formation from the oxidation of biogenic hydrocarbons. J. Geophys. Res. [Atmos.] 1999, 104 (D3), 3555−3567, DOI: 10.1029/ 1998JD100049. (5) Griffin, R. J.; Crocker, D. R.; Seinfeld, J. H.; Dabdub, D. Estimate of global atmospheric organic aerosols from oxidation of biogenic hydrocarbons. Geophys. Res. Lett. 1999, 26 (17), 2721−2724, DOI: 10.1029/1999GL900476. (6) Liao, H.; Henze, D. K.; Seinfeld, J. H.; Wu, S.; Mickley, L. J. Biogenic secondary organic aerosol over the United States: Comparison of climatological simulations with observations. J. 5702

dx.doi.org/10.1021/es204205m | Environ. Sci. Technol. 2012, 46, 5696−5703

Environmental Science & Technology

Article

Management and Impacts in Lodgepole Pine; Safranyik, L, Wilson, B., Eds.; Natural Resources Canada: Victoria, BC, 2006; pp 67−94. (24) Kurz, W. A.; Dymond, C. C.; Stinson, G.; Rampley, G. J.; Neilson, E. T.; Carroll, A. L.; Ebata, T.; Safranyik, L. Mountain pine beetle and forest carbon feedback to climate change. Nature 2008, 452 (7190), 987−990, DOI: 10.1038/nature06777. (25) Westfall, J.; Ebata, T 2007 Summary of Forest Health Conditions in British Columbia; Ministry of Forests and Range, Forest Practices Branch: Victoria, British Columbia, Canada, 2008; http://www.for. gov.bc.ca/ftp/HFP/external/!publish/Aerial_Overview/2008/ Aerial%20Overview%202008.pdf. (26) Logan, J. A.; Powell, J. A Ghost forests, global warming, and the mountain pine beetle. Amer. Entomol. 2001, 47 (3), 160−173. (27) Williams, D. W.; Liebhold, A. M. Climate change and the outbreak ranges of two North American bark beetles. Agr. For. Ent. 2002, 4, 87−99, DOI: 10.1046/j.1461-9563.2002.00124.x. (28) Borys, R. D.; Wetzel, M. A. Storm Peak Laboratory: A research, teaching and service facility for the atmospheric sciences. Bull., Amer. Meteor. Soc. 1997, 78, 2115−2123, DOI: 10.1175/1520-0477(1997) 0782.0.CO;2. (29) Hallar, A. G.; Lowenthal, D. H.; Chirokova., G.; Wiedinmyer, C.; Borys, R. D. Persistent daily new particle formation at a mountaintop location. Atmos. Environ. 2011, 45 (24), 411−4115, DOI: 10.1016/j.atmosenv.2011.04.044. (30) Raguso, R. A.; Pellmyr, O. Dynamic headspace analysis of floral volatiles: A comparison of methods. Oikos 1998, 81 (2), 238−254. (31) Adams, R. P. Identification of Essential Oil Components by Gas Chromatography/Mass Spectrometry; Allured Publishing: Carol Stream, IL, 2007. (32) Sturaro, A.; Parvoli, G.; Doretti, L. Artifacts produced by Porapak Q sorbent tubes on solvent desorption. Chromatographia 1992, 33 (1−2), 53−57, DOI: 10.1007/BF02276852. (33) Sive, B. C.; Zhou, Y.; Troop, D.; Wang, Y. L.; Little, W. C.; Wingenter, O. W.; Russo, R. S.; Varner, R. K.; Talbot, R. W. Development of a cryogen-free concentration system for measurements of volatile organic compounds. Anal. Chem. 2005, 77 (21), 6989−6998, DOI: 10.1021/ac0506231. (34) Russo, R. S.; Zhou, Y.; Haase, K. B.; Wingenter, O. W.; Frinak, E. K.; Mao, H.; Talbot, R. W.; Sive, B. C. Temporal variability, sources, and sinks of C(1)-C(5) alkyl nitrates in coastal New England. Atmos. Chem. Phys. 2010, 10 (4), 1865−1883, DOI: 10.5194/acpd-9-233712009. (35) Russo, R. S.; Zhou, Y.; Haase, K. B.; Wingenter, O. W.; Frinak, E. K.; Mao, H.; Talbot, R. W.; Sive, B. C. Multi-year (2004−2008) record of nonmethane hydrocarbons and halocarbons in New England: seasonal variations and regional sources. Atmos. Chem. Phys. 2010, 10 (10), 4909−4929, DOI: 10.5194/acp-10-4909-2010. (36) Zhou, Y.; Mao, H.; Russo, R. S.; Blake, D. R.; Wingenter, O. W.; Haase, K. B.; Ambrose, J.; Varner, R. K.; Talbot, R. W.; Sive, B. C. Bromoform and dibromomethane measurements in the seacoast region of New Hampshire. 2002−2004. J. Geophys. Res.[Atmos.] 2008, 113 (D8), D08305 DOI: 10.1029/2007JD009103. (37) Gara, R. I.; Littke, W. R.; Rhoades, D. F. Emission of ethanol and monoterpenes by fungal infected lodgepole pine trees. Phytochemistry 1993, 34 (4), 987−990, DOI: 10.1016/S00319422(00)90699-X. (38) Rhoades, D. F. Analysis of monoterpenes emitted and absorbed by undamaged boles of lodgepole pine. Phytochemistry 1990, 29 (5), 1463−1465, DOI: 10.1016/0031-9422(90)80101-L. (39) Jost, R. W.; Rice, A. V.; Langor, D. W.; Boluk, Y. Monoterpene emissions from lodgepole and jack pine bark inoculated with mountain pine beetle-associated fungi. J. Wood Chem. Technol. 2008, 28 (1), 37− 46, DOI: 10.1080/02773810801916407. (40) Atkinson, R.; Arey, J. Atmospheric degradation of volatile organic compounds. Chem. Rev. 2003, 103 (12), 4605−4638, DOI: 10.1021/cr0206420. (41) Surratt, J. D.; Gómez-González, Y.; Chan, A. W. H.; Vermeylen, R.; Shahgholi, M.; Kleindienst, T. E.; Edney, E. O.; Offenberg, J. H.; Lewandowski, M.; Jaoui, M.; Maenhaut, W.; Claeys, M.; Flagan, R. C.;

Seinfeld, J. H. Organosulfate formation in biogenic secondary organic aerosol. J. Phys. Chem. A 2008, 112 (36), 8345−8378, DOI: 10.1021/ jp802310p.

5703

dx.doi.org/10.1021/es204205m | Environ. Sci. Technol. 2012, 46, 5696−5703