Quantification of contributions from various sources of CO is important for understanding the atmospheric CO budget. Considering the number and diversity of sources and sinks, the widely used proxies such as concentration and conventional isotopic compositions (δC and δO) are not always sufficient to fully constrain the CO budget. Additional constraints may help in understanding the mechanisms of CO production and consumption. The anomaly in triple oxygen isotopes or O excess (denoted by ΔO) and molecules containing two rare isotopes, called clumped isotopes, are two recently developed tracers with potentials to independently constrain some important processes that regulate CO in the atmosphere. The clumped isotope for CO, denoted by Δ, is the excess of COO over a random distribution of isotopes in a CO molecule. We measured the concentrations of δC, δO, ΔO, and Δ in air CO samples collected from the Hsuehshan tunnel (length: 12.9 km), and applied linear and polynomial regressions to obtain the fossil fuel end-members for all these isotope proxies. The other end-members, the values of all these proxies for background air CO, are either assumed or taken as the values obtained over the tunnel and ocean. The fossil fuel (anthropogenic) CO end-member values for δC, δO, ΔO, and Δ are estimated using the two component mixing approach: the derived values are -26.76 ± 0.25‰, 24.57 ± 0.33‰, -0.219 ± 0.021‰, and 0.267 ± 0.036‰, respectively. These four major CO isotope tracers along with the concentration were used to estimate the anthropogenic contribution in the atmospheric CO in urban and suburban locations. We demonstrate that ΔO and Δ have the potential to independently estimate anthropogenic contribution, and the advantages of these two over the conventional isotope proxies are discussed.
To advance the capabilities of probing chemical composition aloft, we designed a lightweight remote-controlled whole air sampling component (WASC) and integrated it into a multicopter drone with agile maneuverability to perform aerial whole air sampling. A field mission hovering over an exhaust shaft of a roadway tunnel to collect air samples was performed to demonstrate the applicability of the multicopter-carried WASC apparatus. Ten aerial air samples surrounding the shaft vent were collected by the multicopter-carried WASC. Additional five samples were collected manually inside the shaft for comparison. These samples were then analyzed in the laboratory for the chemical composition of 109 volatile organic compounds (VOCs), CH4, CO, CO2, or CO2 isotopologues. Most of the VOCs in the upwind samples (the least affected by shaft exhaust) were low in concentrations (5.9 ppbv for total 109 VOCs), posting a strong contrast to those in the shaft exhaust (235.8 ppbv for total 109 VOCs). By comparing the aerial samples with the in-shaft samples for chemical compositions, the influence of the shaft exhaust on the surrounding natural air was estimated. Through the aerial measurements, three major advantages of the multicopter-carried WASC were demonstrated: 1. The highly maneuverable multicopter-carried WASC can be readily deployed for three-dimensional environmental studies at a local scale (0-1.5 km); 2. Aerial sampling with superior sample integrity and preservation conditions can now be performed with ease; and 3. Data with spatial resolution for a large array of gaseous species with high precision can be easily obtained.
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