Characterization of water-soluble organic compounds in ambient aerosol using ultrahigh-resolution elctrospray ionization fourier transform ion cyclotron resonance mass spectrometry.

Atmospheric aerosol water-soluble organic compounds (WSOC) exist in a complex mixture of thousands of organic compounds which may have a significant influence on the climate-relevant properties of the atmospheric aerosol. To understand the potential influences, the ambient aerosol was collected at a nonurban mountainous site near Steamboat Springs, CO. The WSOC fraction was analyzed using positive and negative electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. Approximately 2400 and 4000 molecular formulas were identified from the detected positive and negative ions, respectively. The formulas contained carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sulfur (S) atoms over the mass range of 100-800 Da in both ionization modes. The number range of double bond equivalents (DBE), the mean O:C, H:C, and oxidation state of carbon for the positive ions were 0 – 18, 0.25 ± 0.15, 1.39 ± 0.29, and -0.89 ± 0.23, respectively. Comparatively, the negative ion values were 0 – 14, 0.53 ± 0.20, 1.48 ± 0.30, and -0.41 ± 0.45, respectively. Overall, the positive ion molecular formulas were less oxygenated than negative ions as seen with the lower O:C and OSc values. Molecular formulas of the positive ions classified as aliphatic, olefinic, and aromatic compound classes based on the aromaticity index values. Aliphatic compounds were the CHNO and CHO formulas that had mean DBE values of about 5 and 3, respectively. However, a majority of the CHOS, CHNOS, and CHS formulas were defined as olefinic compounds and had mean DBE values of about 12, 13, and 10, respectively. Overall, more than half of the assigned molecular formulas contained sulfur and were olefinic to aromatic compounds with a DBE range of 7-18. Source of the unsaturated sulfur containing compounds is currently unknown. Several nitrogen containing compounds were in common with the field and laboratory studies of the biomass burning aerosol and aged secondary organic aerosol products of the limonene ozonolysis

The Relative Importance of Physicochemical Properties of Organic Contaminants in Aquatic Ecosystems

Measured physical/chemical properties of chemicals can be impacted by varying environmental conditions, subsequently influencing chemical environmental fate and exposure. For example, salinity has been reported to influence the water solubility of organic chemicals entering marine ecosystems. However, there is limited data available on salinity impacts on chemical sorption as well as bioavailability and exposure estimates used in the chemicals regulatory assessment. The salinity impact were demonstrated on the estimates of environmental fate of model compounds with different polarities including pesticides, and polycyclic aromatic sulfur heterocycles (PASHs). The n-octanol/water partition coefficient (KOW) was measured in both distilled-deionized water as well as artificial seawater (3.2%). A linear correlation curve estimated salinity may increase the log KOW value 2.6% per one log unit increase in distilled water (R2 = 0.968). The water solubility, bioconcentration factor, organic carbon soil/sediment sorption coefficient, and acute toxicity in fish were estimated for chemicals using the measured log KOW values by EPI SuiteTM. The water solubility of pesticides was measured in both distilled-deionized water as well as artificial seawater (3.2%). Salinity appears to generally decrease the water solubility and increase partitioning potential. Environmental fate estimates indicate elevated chemical sorption to sediment, bioavailability, and toxicity in artificial seawater suggesting that salinity should be accounted when conducting exposure estimates for marine organisms. In addition, the relative impact of volatilization and hydroxyl radical degradation on estimates of PASH overall dissipation after entry into aquatic ecosystems as a function of depth (0.1, 1 and 2 m) were investigated using the EPA Exposure Analysis Modeling System (EXAMS). The hydroxyl radical rate constant (K.OH) and Henry’s law constant (H) of PASHs were determined in distilled water. Simulated dissipation of PASHs using EXAMS suggest that volatilization is a dominant fate pathway for the higher molecular weight and less polar C2-DBT and C4-DBT at all depths and DBT and C1-DBT at 0.1 m. However, model scenarios suggest hydroxyl radical degradation may significantly contribute to the degradation of more polar DBT and C1-DBT at 1 m and 2 m depths

Ultrahigh-resolution FT-ICR mass spectrometric identification of water-soluble AOM in nonurban organic aerosols

Water-soluble atmospheric organic matter (AOM) is a complex mixture of thousands of organic compounds which may have significant influence on the climate-relevant properties of atmospheric aerosols. To understand the potential influence, the water-soluble fraction of ambient aerosols was analyzed by positive and negative electrospray ionization Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Approximately 4000 negative and 1000 positive chemical formulas were identified. The formulas contained carbon, hydrogen, oxygen, nitrogen, and sulfur atoms over the mass range of 100-800 in both modes. The range of double bond equivalence (DBE) values, the average O/C and H/C ratios of the negative ions were 0-14, 0.53, and 1.48, respectively. The range of DBE values, the average O/C and H/C ratios of the positive ions were 0-17, 0.33, and 1.40, respectively. Despite the range of DBE values, the majority compounds were found in the aliphatic region of the van Krevelen diagram

Water-soluble organic compounds in ambient aerosol: A study using positive ion mode electrospray ionization Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry

Water-soluble organic compounds of atmospheric aerosol were analyzed using positive electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. Ambient aerosol collected at a nonurban high elevation site near Steamboat Springs, CO. Approximately, 2400 molecular formulas were assigned to the positive ions containing carbon, hydrogen, oxygen, nitrogen, and sulfur atoms in the range of m/z 100-800. The double bond equivalents (DBE) range, mean O:C, mean H:C, and oxidation state of carbon were 0 - 18, 0.25 ± 0.15, 1.39 ± 0.29, and -0.89 ± 0.23, respectively. A majority of the CHOS, CHNOS, and CHS formulas were highly unsaturated with mean DBE values of 12, 13, and 10, respectively. A majority of the CHNO and CHO formulas were more saturated with mean DBE values of 5 and 3, respectively. Several CHNO formulas were observed to be common with those of other studies including biomass burning aerosol and aged products of limonene ozonolysis

Chemical and molecular characterization of free tropospheric aerosol sampled at the Pico Mountain Observatory

Improved characterization of free tropospheric aerosol optical, chemical and morphological properties is essential to further our understanding of the aerosol lifecycle and the aerosol-climate implications. Free tropospheric aerosols were studied at the Pico Mountain Observatory, located on top of the Pico volcano in the Azores, Portugal (2225 m asl; 38.47°N, 28.40°W). The station is typically subjected to free tropospheric air masses that are long-range transported from North America. Recently, we deployed a set of four high-volume samplers for the chemical analysis of aerosol, a 3-wavelength nephelometer to measure aerosol light scattering and backscattering fraction, a two channels particle optical counter (for particles larger than 300 nm), and a sequential sampler to collect aerosols on nucleopore membranes and lacy carbon grids for electron microscopy analysis. Black carbon mass equivalent concentrations have been measured at the station since 2001 with a 7-wavelength aethalometer. Summertime daily concentrations of free tropospheric organic carbon, elemental carbon, water-soluble organic carbon (WSOC), anions and cations were measured from high-volume filter samples. Selected WSOC samples were further analysed using ultrahigh resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Molecular formulas were assigned to accurate masses as described in Mazzoleni et al., 2012. Thousands of monoisotopic compounds containing C, H, O, N, and S were identified from the negative and positive ion ultrahigh resolution FT-ICR mass spectra. The comprehensive composition of free tropospheric WSOC was compared to non-urban aerosol samples collected at the Storm Peak Laboratory in the Rocky Mountains of northwestern Colorado (3220 m asl; 40.455°N, -106.744°W). Considerable differences in the elemental ratios and molecular unsaturation were observed. This presentation will discuss those differences and their relationship to aerosol ageing with respect to long-range transport

Identification of water-soluble organic carbon in non-urban aerosols using ultrahigh-resolution FT-ICR mass spectrometry: organic anions

Water-soluble organic carbon (WSOC) is a complex mixture of thousands of organic compounds which may have significant influence on the climate-relevant properties of atmospheric aerosols. An improved understanding of the molecular composition of WSOC is needed to evaluate the effect of aerosol composition upon aerosol physical properties. In this work, ultrahigh-resolution Fourier transform–ion cyclotron resonance mass spectrometry (FT-ICR MS) was used to characterise aerosol WSOC collected during the summer of 2010 at the Storm Peak Laboratory (3210 m ASL) near Steamboat Springs, CO. Approximately 4000 molecular formulas were assigned in the mass range of 100–800 Da after negative-ion electrospray ionisation and more than 50 % of them contained nitrogen or sulfur. The double bond equivalents (DBEs) of the molecular formulas were inversely proportional to the O : C ratio, despite a relatively constant H : C ratio of ~1.5. Despite the range of DBE values, the elemental ratios and the high number of oxygen atoms per formula indicate that a majority of the compounds are aliphatic to olefinic in nature. These trends indicate significant non-oxidative accretion reaction pathways for the formation of high molecular weight WSOC components. In addition, a significant number of molecular formulas assigned in this work matched those previously identified as secondary organic aerosol components of monoterpene and sesquiterpene ozonolysis