Abstract. In black carbon (BC) measurements obtained using the filter-based optical technique, artifacts are a major problem. Recently, it has become possible to correct these artifacts to a certain extent by using numerical methods. Nevertheless, all correction schemes have their advantages and disadvantages under field conditions. In this study, a new correction model that can be used for determining artifact effects on BC measurements was proposed; the model is based on two different light attenuation (ATN) increasing rates. Two aethalometers were used to measure ATN values in parallel at aerosol sampling flow rates of 6 and 2 L min−1. In the absence of sampling artifacts, the ratio of ATN values measured by the two aethalometers should be equal to the ratio of the sampling flow rates (or aerosol deposition rates) of these two aethalometers. In practice, the ratio of ATN values measured by the two aethalometers was not the same as the ratio of the sampling flow rates of the aethalometers because the aerosol loading effects varied with the aerosol deposition rate. If the true ATN value can be found, then BC measurements can be corrected for artifacts by using the true ATN change rate. Therefore, determining the true ATN value was the primary objective of this study. The proposed correction algorithm can be used to obtain the true ATN value from ATN values acquired at different sampling flow rates, and the actual BC mass concentrations can be determined from the true ATN change rate. Before BC correction, the BC concentration measured at the sampling flow rate of 6 L min−1 was smaller than that measured at 2 L min−1 by approximately 13 and 9% in summer and winter seasons, respectively. After BC correction by using the true ATN value, the corrected BC for 6 L min−1 can be exactly equal to the corrected BC for 2 L min−1. Field test results demonstrated that loading effects on BC measurements could be corrected accurately by using the proposed model. Additionally, the problem of enhanced light ATN caused by light scattering at the unloaded filter can be overcome without using any light scattering coefficient. Therefore, the correction algorithm can be applied to a newly designed instrument to determine actual real-time BC concentrations by using two sampling spots for different aerosol deposition rates. Moreover, a simple empirical correction scheme for post-processing for correcting the existed aethalometer BC data is also presented. While this simple correction scheme is dependent on the aerosol type, it can be used to correct BC data when the primary source of BC and the weather conditions are similar to those in this study. Furthermore, two existed aethalometers with appropriate flow control can be used to create correction schemes suitable for different environments.
The Yanshui Beehive Firework Festival is a traditional folk activity in Southern Taiwan held during the Lantern Festival, and it is the third largest folk celebration in the world. During this festival, more than 200 firecracker towers with hundreds of thousands of firecrackers are ignited, posing a risk to public health because of an abrupt increase in particulate matter concentrations within a short period. In this study, real-time variations of PM 2.5 (particles with an aerodynamic diameter less than or equal to 2.5 µm), black carbon (BC), and particle number concentrations were monitored before and during the firework display to understand the effect of the firework display on the short-term air quality. The hourly average concentrations of PM 2.5 , BC, total particle number, and ultrafine particle number during the firework display (episode period) were 146.9 µg m -3 , 2639 ng m -3 , 3.37 × 10 4 # cm -3 , and 1.18 × 10 4 # cm -3 , respectively. These values were 6.9, 2.3, 5.9, and 3.7 times greater than those during the same period on reference days (nonepisode period), respectively. The measured ultraviolet BC (UVBC) and BC concentrations indicated that aerosols were bound with ultraviolet-absorbing organic compounds, which were abundant, during the episode period. BC aerosols during the episode originated from vehicular traffic and firecracker burning, and the absorption Ångström exponent value was 1.4. The particle number size distribution during the episode period showed a major accumulation mode and a minor Aitken mode of 180 and 63 nm, respectively. This particle number size distribution pattern was considerably different from that in the nonepisode period. During the episode period, particle coagulation played a crucial role in removing particles in the nucleation and Aitken modes in the ambient air at high particle number concentrations.
Information on the effect of open-field burning of agricultural residues on ambient black carbon (BC) mass and size-resolved particle number concentrations is scarce. In this study, to understand the effect of such open-field burning on short-term air quality, real-time variations of the BC mass and size-resolved particle number concentrations were monitored before and during a corn straw open-field burning episode at a rural site. Correlations between the BC mass and size-resolved particle number concentrations during the episode were investigated. Moreover, the particle number size distribution and absorption Ångström exponent were determined for obtaining the characteristics of aerosol emissions from the corn straw open-field burning. The results can be used to address public health concerns and as a reference for managing similar episodes of open-field burning of agricultural residues.
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