Stable<sup>15</sup>N isotopes in fine and coarse urban particulate matter

A series of student-led research activities were performed using a cargo bicycle equipped with air chemistry instrumentation to study the dynamics of aerosol particles in urban air before, during, and after the COVID-19 lockdown periods. The studies examined a high-traffic route and a low-traffic route around the city center of Münster, Germany. A complex picture emerged for how the particle number concentrations (PN) and particle mass concentrations (PM, specifically PM10) were affected by the day of the week, the route selected, the meteorological conditions, and the traffic intensity. Traffic had the most impact on PN through the multitude of exhaust plumes from motorized vehicles. The impact of traffic on PM10 was rather low, which is also mirrored in the general pattern of the low response of PM10 to the pandemic lockdown in Germany. Instead, PM10 responded more to the day of the week. Presumably, PM10 responds either to a specific traffic component, such as commercial low-duty vehicles, or to other business, such as construction activity. Meteorological conditions exert their impact mostly through the relative humidity, which affects particle growth. As such, future research could examine PN and PM10 responses over all seasons of the year. In any case, this student-led study in which high-resolution data were acquired deepened our understanding and broadened our view on particle dynamics in urban air. Well-trained university graduates will contribute to meeting further challenges in studying and combatting air pollution.

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The Impact of Traffic and Meteorology on Urban Particle Mass and Particle Number Concentrations: Student-Led Studies Using Mobile Measurements before, during, and after the COVID-19 Pandemic Lockdowns

Klemm

Ahrens

Arnswald

et al. 2021

Atmosphere

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Different physicochemical behaviors of nitrate and ammonium during transport: a case study on Mt. Hua, China

Cao

et al. 2022

Atmos. Chem. Phys.

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Abstract. To understand the chemical evolution of aerosols in the transport process, the chemistry of PM2.5 and nitrogen isotope compositions on the mountainside of Mt. Hua (∼1120 m above sea level, a.s.l.) in inland China during the 2016 summertime were investigated and compared with parallel observations collected at surface sampling site (∼400 m a.s.l.). The PM2.5 exhibited a high level at the mountain foot site (MF; average 76.0±44.1 µg m−3) and could be transported aloft by anabatic valley winds, leading to the gradual accumulation of daytime PM2.5 with a noon peak at the mountainside sampling site (MS). As the predominant ion species, sulfate exhibited nearly identical mass concentrations at both sites, but its PM2.5 mass fraction was moderately enhanced by ∼4 % at the MS site. The ammonium variations were similar to the sulfate variations, the chemical forms of both of which mainly existed as ammonium bisulfate (NH4HSO4) and ammonium sulfate ((NH4)2SO4) at the MF and MS sites, respectively. Unlike sulfate and ammonium, nitrate mainly existed as ammonium nitrate (NH4NO3) in fine particles and exhibited decreasing mass concentration and proportion trends with increasing elevation. This finding was ascribed to NH4NO3 volatilization, in which gaseous HNO3 from semi-volatile NH4NO3 subsequently reacted with dust particles to form nonvolatile salts, resulting in significant nitrate shifts from fine particles into coarse particles. Such scavenging of fine-particle nitrate led to an enrichment in the daytime 15N of nitrate at the MS site compared with to the MF site. In contrast to nitrate, at the MS site, the 15N in ammonium depleted during the daytime. Considering the lack of any significant change in ammonia (NH3) sources during the vertical transport process, this 15N depletion in ammonium was mainly the result of unidirectional reactions, indicating that additional NH3 would partition into particulate phases and further neutralize HSO4- to form SO42-. This process would reduce the aerosol acidity, with a higher pH (3.4±2.2) at the MS site and lower ones (2.9±2.0) at the MF site. Our work provides more insight into physicochemical behaviors of semi-volatile nitrate and ammonium, which will facilitate the improvement in the model for a better simulation of aerosol composition and properties.

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Stable¹⁵N isotopes in fine and coarse urban particulate matter

Abstract: Stable15 N isotopes in fine and coarse urban particulate matter, Aerosol Science and Technology,

Cited by 2 publications

References 45 publications

The Impact of Traffic and Meteorology on Urban Particle Mass and Particle Number Concentrations: Student-Led Studies Using Mobile Measurements before, during, and after the COVID-19 Pandemic Lockdowns

The Impact of Traffic and Meteorology on Urban Particle Mass and Particle Number Concentrations: Student-Led Studies Using Mobile Measurements before, during, and after the COVID-19 Pandemic Lockdowns

Different physicochemical behaviors of nitrate and ammonium during transport: a case study on Mt. Hua, China

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Stable15N isotopes in fine and coarse urban particulate matter

Abstract: Stable15 N isotopes in fine and coarse urban particulate matter, Aerosol Science and Technology,

Cited by 2 publications

References 45 publications

The Impact of Traffic and Meteorology on Urban Particle Mass and Particle Number Concentrations: Student-Led Studies Using Mobile Measurements before, during, and after the COVID-19 Pandemic Lockdowns

The Impact of Traffic and Meteorology on Urban Particle Mass and Particle Number Concentrations: Student-Led Studies Using Mobile Measurements before, during, and after the COVID-19 Pandemic Lockdowns

Different physicochemical behaviors of nitrate and ammonium during transport: a case study on Mt. Hua, China

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Stable¹⁵N isotopes in fine and coarse urban particulate matter