Anthropogenic-Biogenic Interactions at Night: Enhanced Formation of Secondary Aerosols and Particulate Nitrogen- and Sulfur-Containing Organics from β-Pinene Oxidation.

Li Xu,Christian George,Narcisse T Tsona,Lin Du,Xinke Wang,Zhaomin Yang

doi:10.1021/acs.est.0c07879

Abstract

Mixing of anthropogenic gaseous pollutants and biogenic volatile organic compounds impacts the formation of secondary aerosols, but still in an unclear manner. The present study explores secondary aerosol formation via the interactions between β-pinene, O3, NO2, SO2, and NH3 under dark conditions. Results showed that aerosol yield can be largely enhanced by more than 330% by NO2 or SO2 but slightly enhanced by NH3 by 39% when the ratio of inorganic gases to β-pinene ranged from 0 to 1.3. Joint effects of NO2 and SO2 and SO2 and NH3 existed as aerosol yields increased with NO2 but decreased with NH3 when SO2 was kept constant. Infrared spectra showed nitrogen-containing aerosol components derived from NO2 and NH3 and sulfur-containing species derived from SO2. Several particulate organic nitrates (MW 215, 229, 231, 245), organosulfates (MW 250, 264, 280, 282, 284), and nitrooxy organosulfates (MW 295, 311, 325, 327, and 343) were identified using high-resolution orbitrap mass spectrometry in NO2 and SO2 experiments, and their formation mechanism is discussed. Most of these nitrogen- and sulfur-containing species have been reported in ambient particles. Our results suggest that the complex interactions among β-pinene, O3, NO2, SO2, and NH3 during the night might serve as a potential pathway for the formation of particulate nitrogen- and sulfur-containing organics, especially in polluted regions with both anthropogenic and biogenic influences.

Highlights

While increasing attention has been paid to the synergistic effects of NH3 with SO2 or with NO2 in the photooxidation of some anthropogenic volatile organic compounds (VOCs), such interactions in biogenic particle formation should be further investigated.[48−51] β-pinene with a global annual emission rate of 18.9 Tg contributes to about 17% of monoterpene in the atmosphere.[7,52]
NO3 radicals, which could be quickly formed via NO2 + O3 reaction, are more likely to explain such an enhancive NO2 effect on particle formation rate and final mass due to its 5 orders of magnitude higher reactivity with β-pinene and higher secondary organic aerosol (SOA) formation potential compared with β-pinene ozonolysis.[33,77−80]
Our results suggest that β-pinene could be an important contributor to the enhanced SOA formation at night in these places with high anthropogenic NOx emissions

Summary

INTRODUCTION

Aerosol particles in the atmosphere have negative impacts on regional air quality, climate change, and human health.[1,2]. NH3 is another gaseous inorganic pollutant that has been observed to correlate well with the peak level of secondary particle pollution.[40,41] Laboratory studies showed that NH3 tended to enhance SOA mass yield of α-pinene and limonene ozonolysis by forming nitrogen-containing compounds, but no clear associations of NH3 with isoprene SOA were observed.[42−46] It has been predicted that 50% reduction in NH3 together with a 15% reduction in NOx and SO2 could result in a decrease of particulate matter by 11−17% in China.[47] While increasing attention has been paid to the synergistic effects of NH3 with SO2 or with NO2 in the photooxidation of some anthropogenic VOCs, such interactions in biogenic particle formation should be further investigated.[48−51] β-pinene with a global annual emission rate of 18.9 Tg contributes to about 17% of monoterpene in the atmosphere.[7,52] Its atmospheric abundance and exocyclic double bond make it a common representative of exocyclic monoterpenes.[53] The ozonolysis of β-pinene at night has been observed to have a significant contribution to nocturnal nucleation.[54,55] In the present study, laboratory experiments were conducted to explore the effects of inorganic pollutants on aerosol formation initiated by nucleation during β-pinene ozonolysis in the absence of seed particles. Formation pathways of the specific particulate products, including nitrogenand sulfur-containing compounds, were proposed to further reveal the effects of NO2, SO2, and NH3 on aerosol composition

EXPERIMENTAL METHODS

RESULTS AND DISCUSSION

ATMOSPHERIC IMPLICATION