Research

Projects:
Isomer-specific Measurements of Isoprene Oxidation Products
Halocarbons in the LA Basin
Isotopes in the Sierra Nevada Snowfall
Soil Nitrite Extraction Methods

Isomer-specific Measurements of Isoprene Oxidation Products

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Project Dates: Jan 2016 – Present

Due to its large emissions and high reactivity, isoprene dominates the chemistry of a number of atmospheric species. Its strong influence is primarily due to the formation of six isomeric peroxy radicals (ISOPOO) whose subsequent fates is critical in determining the budgets of important compounds such as ozone, NOx and secondary organic aerosols (SOA). However, current analytical methods are not able to distinguish between the different ISOPOO isomers nor their resulting products. Thus, I have helped develop new instrumentation that combines chromatographic separation with high resolution mass spectrometry in order to provide the first in situ, real-time isomer distributions of various isoprene oxidation products.

Field Campaign(s):

Related Presentation(s):

  • Vasquez, K., Allen, H., Crounse, J.D., Praske, E., Xu, L., Nölsher, A., Bates, K., & Wennberg, P.O.  (December 2017) Investigation of Isomer Specific Sinks for Isoprene Oxidation Products in varying NOx Environments. Poster presented at the 2017 AGU Fall Meeting, New Orleans, LA
  • Vasquez, K., Allen, H., Nölsher, A., Praske, E., Bates, K., Crounse, J.D., & Wennberg, P.O.  (February 2017) Investigation of Isomer Specific Sinks for Isoprene Oxidation Products. Poster presented at the UMBS Winter Research Meeting, Ann Arbor, MI.

Halocarbons in the LA Basin

halocarbons

Project Dates: Jun 2014 – Aug 2014

Capture The phase-out of CFCs due to the Montreal Protocol gave way to the introduction of industrial HCFCs, HFCs and other halocarbons. Though these replacement compounds are much shorter-lived than their CFC counterparts, they are still classified as greenhouse gases and some even have the potential to deplete stratospheric ozone. In this study, airborne samples collected over the LA Basin during SARP flights from 2011-2014 were analyzed for three purely anthropothenic gases—perchloroethylene, HCFC-22, and HFC-134a—and then coupled to AGAGE data during the same years in order to show LA Basin’s contribution to this increasing trend.Capture2 Data show that in the LA Basin two of these gases (perchloroethylene and H-134a) are all increasing at a rate higher than that reported from AGAGE, whereas HCFC-22 was not. For example, HFC-134a sampled within the planetary boundary layer has increased at 11.8 pptv/year, compared to an AGAGE value of 4.85 pptv/year. These results demonstrate that the LA Basin contributes greatly to the global load of HCFCs. Additionally, this study shows uncharacteristic emissions of H-1301 near the Long Beach and Los Alamitos Airports. Furthermore, a 92 pptv concentration of H-1301 was observed at Los Alamitos during an afternoon missed approach. This is much higher than morning concentrations being near background levels (~3-4 pptv). This is likely due changes in direction of low altitude winds.

Related Presentation(s):

  • Vasquez, K., Marrero, J., & Blake, D. (August 2014) The Los Angeles Basin as a Source of Long-Lived Greenhouse Gases. Talk for the NASA Student Airborne Research Program, Irvine, CA.

Isotopes in the Sierra Nevada Snowfall

sequoia

Project Dates: Oct 2012 – Jun 2015

Capture3

Understanding past and future variations in the Sierra Nevada snowpack is crucial in order to plan future water management. Of particular importance would be an archive of past snowfall variability, which can be recorded through isotopic records found in local paleoproxies (e.g. diatoms). We proposed to quantify the relationship between sources of Sierra Nevada precipitation events and the isotopic composition of its snowpack in order to uncover if isotopic variations recorded in these archives could serve as reliable indicators of past atmospheric moisture sources.

Capture4Analysis conducted during Winter 2012-13 of individual storm events occurring in Lodgepole, CA (Southern Sierra Nevada) showed a statistically significant correlation between the isotopic composition of the snowfall and the storm track trajectory (R2 = 0.8027). This promising find indicated that there was climatic significance in the isotopic analysis of proxies of the area. However, archived samples from calendar years 2007-2008 obtained from the National Atmospheric Deposition Program (NADP) contrasted our preliminary findings, showing no significant correlation between the variables. We believe however that this may not be due to a lack of statistical relationship, but rather caused by the method of collection reduced the observed signal by incorporating several storm events into a single sample. Furthermore, the variations of sea surface temperature (SST) caused by Pacific circulation events that took place in 2007-2008 could have also created some discrepancy.

Related Presentation(s):

  • Vasquez, K., Sickman, J.O., Heard, A., & Lucero, D. (April 2015) Relationship between trajectory of mid-latitude cyclones in the eastern Pacific Ocean and the isotopic composition of snowfall in the Sierra Nevada. Talk at the 2015 Undergraduate Education Research Symposium, Riverside, CA. [Link]
  • Vasquez, K.,Sickman, J.O., Heard, A., & Lucero, D. (December 2014) Relationship between trajectory of mid-latitude cyclones in the eastern Pacific Ocean and the isotopic composition of snowfall in the Sierra Nevada. Poster at the American Geophysical Union Fall Meeting, San Franscisco, CA. [Link]
  • Vasquez, K. & Sickman, J.O. (April 2013) Fingerprinting the Sierra Snowpack: Relationship between Storm Tracks and the Isotopic Composition of Snow. Poster presented at the 2013 Undergraduate Research Symposium, Riverside, CA. [Link]

Soil Nitrite Extraction Methods

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Project Dates: Oct 2012 – Jun 2015

Soil nitrite (NO2) is an important source of nitrous acid to the atmosphere as well an intermediate in nitrification and denitrification. Few studies, however, have directly linked NO2 pools with N emissions because NO2 is reactive and seldom detectable in soils. Here, we test whether the elusiveness of soil NO2 is due to its reactivity or to problems associated with conventional 2 M KCl extractions. We extracted acidic, neutral, and alkaline soils (pH 5.4– 8.2) in 2 M KCl, pH-8-adjusted 2 M KCl, and deionized water (DIW). Unbuffered KCl consistently underestimated soil NO2 compared with DIW; soils with lower pH had lower NO2 in unbuffered KCl than in DIW water. In acidic soils, unbuffered KCl favored the transformation of NO2 to nitric oxide. Because KCl lowers the pH of extracts by ∼1 unit, this increase in acidity likely favored the transformation of NO2 to gaseous N products. Although buffered KCl minimizes NO2 destruction, it can cause colorimetric interferences when done on small soil samples (4 g). Deionized water extractions offer an alternative for measuring NO2 in small samples, but filtering beyond the traditionally used 2.5-μm filter paper is necessary to remove suspended solids. Despite its widespread use, unbuffered 2 M KCl should not be used for the analysis of soil NO2.

Related Publication(s):

  • Homyak, P., Vasquez, K., Sickman, J.O., Parker, D., Schimel, J. (May 2015) Improving Nitrite Analysis in Soils: Drawbacks of the Conventional 2M KCl Extraction Technique. Soil Science Society of America Journal 79(4): 1237-1242. [Link]
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