Potential dual effect of anthropogenic emissions on the formation of biogenic secondary organic aerosol (BSOA)

Abstract

Abstract. The fraction of gasoline direct-injection (GDI) vehicles comprising the total vehicle pool is projected to increase in the future. However, thorough knowledge about the influence of GDI engines on important atmospheric chemistry processes is missing – namely, their contribution to secondary organic aerosol (SOA) precursor emissions, contribution to SOA formation, and potential role in biogenic–anthropogenic interactions. The objectives of this study were to (1) characterize emissions from modern GDI vehicles and investigate their role in SOA formation chemistry and (2) investigate biogenic–anthropogenic interactions related to SOA formation from a mixture of GDI-vehicle emissions and a model biogenic compound, α-pinene. Specifically, we studied SOA formation from modern GDI-vehicle emissions during the constant-load driving. In this study we show that SOA formation from GDI-vehicle emissions was observed in each experiment. Volatile organic compounds (VOCs) measured with the proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) could account for 19 %–42 % of total SOA mass generated in each experiment. This suggests that there were lower-volatility intermediate VOCs (IVOCs) and semi-volatile organic compounds (SVOCs) in the GDI-vehicle exhaust that likely contributed to SOA production but were not detected with the instrumentation used in this study. This study also demonstrates that two distinct mechanisms caused by anthropogenic emissions suppress α-pinene SOA mass yield. The first suppressing effect was the presence of NOx. This mechanism is consistent with previous reports demonstrating suppression of biogenic SOA formation in the presence of anthropogenic emissions. Our results indicate a possible second suppressing effect, and we suggest that the presence of anthropogenic gas-phase species may have suppressed biogenic SOA formation by alterations to the gas-phase chemistry of α-pinene. This hypothesized change in oxidation pathways led to the formation of α-pinene oxidation products that most likely did not have vapor pressures low enough to partition into the particle phase. Overall, the presence of gasoline-vehicle exhaust caused a more than 50 % suppression in α-pinene SOA mass yield compared to the α-pinene SOA mass yield measured in the absence of any anthropogenic influence.

Direct contribution of ammonia to CCN-size alpha-pinene secondary organic aerosol formation

“…SOA experiments were conducted in the ILMARI environmental chamber infrastructure in University of Eastern Finland. The experimental system and experimental procedure have been described in details in Leskinen et al (2015) and Kari et al (2019a), respectively. The chamber consists of a 29 m 3 Teflon TM FEP film bag.…”

“…The seed was generated using an atomizer (Topas ATM226, Germany). In two experiments, nitrogen oxide (NO) was added to chamber, and ozone (O3) was introduced into the chamber to convert NO to nitrogen dioxide (NO2) to reach the atmospherically relevant NO2-to-NO ratio of ~ 3 (Kari et al, 2019a). After O3 and NOx were fed, 85 3 µl 9-fold butanol (butanol-d9, 98 %, Sigma Aldrich) was injected to the chamber, from whose consumption the hydroxyl radical (OH) exposure was estimated in each experiment (Kari et al, 2019a).…”

“…In two experiments, nitrogen oxide (NO) was added to chamber, and ozone (O3) was introduced into the chamber to convert NO to nitrogen dioxide (NO2) to reach the atmospherically relevant NO2-to-NO ratio of ~ 3 (Kari et al, 2019a). After O3 and NOx were fed, 85 3 µl 9-fold butanol (butanol-d9, 98 %, Sigma Aldrich) was injected to the chamber, from whose consumption the hydroxyl radical (OH) exposure was estimated in each experiment (Kari et al, 2019a). Next, 1 µl and 18 µl of αpinene (≥ 99%, Sigma Aldrich) were added into the chamber for the seeded and nucleation SOA experiments, respectively, corresponding to concentrations of ⁓5 ppb and ⁓100 ppb of α-pinene in the chamber.…”

“…A detailed description of the instrument and operation procedure has been provided in Jordan et al (2009) and Kari et al (2019a;2019b). In brief, the PTRMS instrumental setting were the same as in Kari et al (2019a).…”

“…A detailed description of the instrument and operation procedure has been provided in Jordan et al (2009) and Kari et al (2019a;2019b). In brief, the PTRMS instrumental setting were the same as in Kari et al (2019a). During measurement, the mass calibration was conducted using protonated water isotope signals at m/z 21 and internal 115 instrumental signals of diiodobenzene and its fragment ions (protonated integer m/z 331).…”