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Although biochar application to soils has been found to increase soil quality and crop yield, the biochar dispersion extent and its impacts on native soil organic carbon (SOC) has received relatively little attention. Here, the vertical and lateral migration of fine, intermediate and coarse-sized biochar (<0.5, 0.5–1 and 1–5 mm, respectively), applied at low and high doses (1.5–2 and 3–4% w/w, respectively), was tracked using stable isotope methods, along with its impact on native SOC stocks. Biochar was homogeneously mixed into the surface layer (0–7 cm depth) of a loamy sandy Acrisol in Zambia. After 4.5 y, 38–75% of the biochar carbon (BC) was lost from the applied layer and 4–25% was detected in lower soil layers (7–30 cm). Estimating BC mineralization to be no more than 8%, 25–60% was likely transported laterally out of the experimental plots. This conclusion was supported by observations of BC in the control plot and in soils up to 2 m outside of the experimental plots. These processes were likely progressive as recovery of BC in similar plots 1 year after application was greater in both surface and lower soil layers than after 4.5 y. Fine and intermediate-sized BC displayed the greatest downward migration (25.3 and 17.9%, respectively), particularly when applied at lower doses, suggesting its movement through soil inter-particle spaces. At higher dosages, fine and intermediate-sized particles may have clogged pore, so coarse biochar displayed the greatest downward migration when biochar was applied at higher doses. In the BC treatment plot soil profiles, native SOC stocks were reduced by 2.8 to 24.5% (18.4% on average), i.e. positive priming. However, some evidence suggested that the soils may switch to negative priming over time. The dispersion of biochar in soil should be considered when evaluating biochar's agronomic benefits and environmental effects. [ABSTRACT FROM AUTHOR]

The recently developed time-of-flight aerosol chemical speciation monitor with a capture vaporizer and a PM 2.5 aerodynamic lens (TOF-ACSM-CV-PM 2.5) aims to improve the collection efficiency and chemical characterization of aerosol particles with a diameter smaller than 2.5 µm. In this study, comprehensive cross-comparisons were performed between real-time online measurements and offline filter analysis with 24 h collection time. The goal was to evaluate the capabilities of the TOF-ACSM-CV-PM 2.5 lens, as well as the accuracy of the TOF-ACSM-CV-PM 2.5. The experiments were conducted at Cabauw Experimental Site for Atmospheric Research (CESAR) during the RITA-2021 campaign. The non-refractory fine particulate matter (PM 1.0 and PM 2.5) was measured by two collocated TOF-ACSM-CV-PM 2.5 instruments by placing them behind a PM 2.5 and PM 1.0 inlet, respectively. A comparison between the ACSMs and PM 2.5 and PM 1.0 filter samples showed a much better accuracy than ±30 % less given in the previous reports, with average differences less than ±10 % for all inorganic chemical species. In addition, the ACSMs were compared to the Monitoring Instrument for Aerosol and Gas (MARGA) (slope between 0.78 and 0.97 for inorganic compounds, R2≥ 0.93) and a mobility particle size spectrometer (MPSS), measuring the particle size distribution from around 10 to 800 nm (slope was around 1.00, R2= 0.91). The intercomparison of the online measurements and the comparison between the online and offline measurements indicated a low bias (< 10 % for inorganic compounds) and demonstrated the high accuracy and stability of the TOF-ACSM-CV-PM 2.5 lens for the atmospheric observations of particle matter. The two ACSMs exhibited an excellent agreement, with differences less than 7 %, which allowed a quantitative estimate of PM 1.0 vs. PM 2.5 chemical composition. The result showed that the PM 1.0 accounted for about 70 %–80 % of the PM 2.5 on average. The NO 3 mass fraction increased, but the organic carbon (OC) mass fraction decreased from PM 1.0 to PM 2.5 , indicating the size dependence on chemical composition. [ABSTRACT FROM AUTHOR]

The recently developed time of flight-aerosol chemical speciation monitor with the capture vaporizer and a PM2.5 aerodynamic lens (TOF-ACSM-CV-PM2.5) aims to improve the collection efficiency and chemical characterization of aerosol particles with diameter smaller than 2.5µm. In this study, comprehensive cross-comparisons were performed between real-time online measurements and offline filter analysis with 24-hour collection time. The goal was to evaluate the capabilities of the TOFACSM-CV-PM2.5 lens, as well as the accuracy of the TOF-ACSM-CV-PM2.5. The experiments were conducted at Cabauw Experimental Site for Atmospheric Research (CESAR) during the RITA-2021 campaign. The non-refractory fine particulate matter PM1.0 and PM2.5 were measured by two co-located TOF-ACSM-CV-PM2.5 by placing them behind a PM2.5 and PM1.0 inlet, respectively. A comparison between the ACSMs and PM2.5 and PM1.0 filter samples showed a much better accuracy than ±30% less given in the previous reports, with average differences less than ± 10% for all inorganic chemical species. In addition, the ACSMs were compared to a Monitoring Instrument for Aerosol and Gas (MARGA) (slope between 0.78 - 0.97 for inorganic compounds, R2 = 0.93), and a Mobility Particle Size Spectrometer (MPSS) measuring the particle size distribution from around 10 to 800 nm (slope was around 1.00, R2 = 0.91). The intercomparison of the online measurements and the comparison between the online and offline measurements indicated a low bias (< 10% for inorganic compounds) and demonstrated the high accuracy and stability of the TOF-ACSM-CV-PM2.5 lens for the atmospheric observations of particle matters. The two ACSMs exhibited an excellent agreement, with differences less than 7%, which allowed a quantitative estimate of PM1.0 vs PM2.5 chemical composition. The result showed that the PM1.0 accounted for about 70-80% of the PM2.5 on average. The NO3 mass fraction increased but the OC mass fraction decreased from PM1.0 to PM2.5, indicating the size30 dependence on chemical composition. [ABSTRACT FROM AUTHOR]

The recently developed time of flight-aerosol chemical speciation monitor with the capture vaporizer and a PM2.5 aerodynamic lens (TOF-ACSM-CV-PM2.5) aims to improve the collection efficiency and chemical characterization of aerosol particles with a diameter smaller than 2.5 µm. In this study, comprehensive cross-comparisons were performed between real-time online measurements and offline filter analysis with 24-hour collection time. The goal was to evaluate the capabilities of the TOF-ACSM-CV-PM2.5 lens, as well as the accuracy of the TOF-ACSM-CV-PM2.5. The experiments were conducted at Cabauw Experimental Site for Atmospheric Research (CESAR) during the RITA-2021 campaign. The non-refractory fine particulate matter PM1.0 and PM2.5 were measured by two co-located TOF-ACSM-CV-PM2.5 by placing them behind a PM2.5 and PM1.0 inlet, respectively. A comparison between the ACSMs and PM2.5 and PM1.0 filter samples showed a much better accuracy than ±30 % less given in the previous reports, with average differences less than ± 10 % for all inorganic chemical species. In addition, the ACSMs were compared to a Monitoring Instrument for Aerosol and Gas (MARGA) (slope between 0.78–0.97 for inorganic compounds, R2 ≥ 0.93), and a Mobility Particle Size Spectrometer (MPSS) measuring the particle size distribution from around 10 to 800 nm (slope was around 1.00, R2 = 0.91). The intercomparison of the online measurements and the comparison between the online and offline measurements indicated a low bias (< 10 % for inorganic compounds) and demonstrated the high accuracy and stability of the TOF-ACSM-CV-PM2.5 lens for the atmospheric observations of particle matters. The two ACSMs exhibited an excellent agreement, with differences less than 7 %, which allowed a quantitative estimate of PM1.0 vs PM2.5 chemical composition. The result showed that the PM1.0 accounted for about 70–80 % of the PM2.5 on average. The NO3 mass fraction increased but the OC mass fraction decreased from PM1.0 to PM2.5, indicating the size-dependence on chemical composition. [ABSTRACT FROM AUTHOR]

Elevated nitrogen (N) deposition and changes in reduced or oxidized component contribution greatly affect soil acidification. China has experienced a significant transformation of N deposition components from NHx to NOy over the past 40 years, but the effects of component transformation on soil acidification are poorly understood. Therefore, long‐term monitoring data and literature on N deposition, combined with the results of isotope experiments, were used to explore the contributions of different N forms on soil acidification in China's forests. Here, all processes related to NHx and NOy, including the transformation to NH4+ and NO3− and subsequent N cycling in the soil, were considered. We found that N‐induced soil acidification in 80% area of China's forests was dominated by NHx deposition, and the other areas (South China) were dominated by NOy deposition in 2010s. From 1980 to 2019, the average contribution of NHx was higher than that of NOy but the latter contribution continued to increase. Meanwhile, the results showed that soil acidification increased with the decrease of the ratio of NHx to NOy (RNHx/NOy), which is mainly because NOy is more easily leached in the form of NO3− than that of NHx under the influence of different plant preferences and soil retention rates, resulting in a higher net proton production of NOy. Our research has powerful implications for policymaking, provides a theoretical basis for formulating different N reduction policies in different regions, and points out that the synergistic effect of RNHx/NOy changes should be considered to alleviate soil acidification. Key Points: Most forest soil was dominated by the contribution of NHx deposition, causing soil acidificationThe contribution of NOy deposition to soil acidification increased continuously during 1980–2019Decreased ratio of NHx to NOy deposition has led to aggravated forest soil acidification [ABSTRACT FROM AUTHOR]