Relationship between the amount of black carbon particles deposited on the leaf surface and leaf surface traits in nine urban greening tree species.

To select urban greening tree species suitable for the purification of the atmosphere polluted by black carbon (BC) particles, it is necessary to clarify the determinants of the amount of BC particles deposited on the tree leaves. In the present study, we investigated the relationship between the amount of BC particles that were deposited from the atmosphere and firmly adhered to the leaf epicuticular wax, and leaf surface traits in seedlings of nine tree species grown for two years under natural conditions (Fuchu, Tokyo, Japan). There was a significant interspecific difference in the maximum amount of BC particles deposited on the leaf surface, and the order was as follows: Ilex rotunda > Cornus florida > Osmanthus fragrans > Cornus kousa > Quercus glauca ≒ Quercus myrsinifolia > Magnolia kobus ≒ Zelkova serrata ≒ Styrax japonicus. In the nine tree species, significant highly positive correlations were observed between the amount of BC particles deposited on the leaf surface, and the hydrophobicity of leaf epicuticular wax determined by its chemical composition. Therefore, we concluded that the hydrophobicity of leaf epicuticular wax is an important determinant of the amount of BC particles deposited on the leaf surface of urban greening tree species.

This is the first paper that shows that the hydrophobicity of leaf epicuticular wax is an important determinant of the amount of BC particles deposited on the leaf surface of urban greening tree species. This study will provide the basic and novel information for the selection of urban greening tree species suitable for the purification of the air polluted by BC particles.

Seasonal variations in the amount of black carbon particles deposited on the leaf surfaces of nine Japanese urban greening tree species and their related factors.

As black carbon (BC) particles can be deposited on the leaf surfaces, urban greening is considered to be effective in purifying urban air. However, little information on the seasonal variations in the amount of BC particles deposited on the leaf surfaces (BC amount on the leaves) is available in Japanese urban greening tree species. Therefore, we investigated seasonal variations in the BC amount on the leaves of evergreen (Quercus glauca, Quercus myrsinaefolia, Osmanthus fragrans and Ilex rotunda) and deciduous (Zelkova serrata, Styrax japonica, Magnolia kobus, Cornus kousa and Cornus florida) broad-leaved tree species. The BC amount on the leaves tended to increase from April for different periods, and then reached a saturated state in the tree species, excluding M. kobus. In the 4 evergreen broad-leaved trees, the seasonal variation was positively correlated with the atmospheric concentration of BC particle. In the 5 deciduous broad-leaved trees, the seasonal variation was negatively and positively correlated with the water-repellence (water droplet contact angle) and the amount of epicuticular wax on the leaf surface, respectively. Therefore, the BC amounts on the leaves of evergreen and deciduous broad-leaved urban tree species are considered to be mainly regulated by environmental factors and leaf surface characteristics, respectively.

This is the first paper that reports the seasonal variations in the amount of BC particles deposited on the leaves of Japanese urban greening tree species and their related factors such as environmental conditions and leaf surface characteristics. This study will provide the basic and novel information for the phytoremediation of urban air pollution induced by BC particles in Asia.

A twenty-year deposition record of elemental carbon in Northern Japan retrieved from archived filters.

The black carbon or elemental carbon (EC) content in ice and snow has been a concern in climate change studies, but time-series records have mostly been obtained from glacier ice-core samples in limited geographical locations, such as the Arctic or high mountains. This is the first study to present decade-long records of EC deposition measured at urban (Sapporo) and background (Rishiri Island) sites in Japan, in the mid-latitude zone of the eastern edge of the Asian continent. By using archived membrane filters from an acid rain study, we retrieved monthly EC deposition records of 1993-2012 in Sapporo and intermittent deposition data in Rishiri. Annual EC deposition showed large fluctuations, with a maximum in 2000-2001 and a minor increase in 2010-2011. This interannual change was moderately related to the deposition of non-sea salt SO42- and the collected water volume but did not reflect the estimated emission history of China. High depositions in 2000-2001 were probably caused by the transport of Asian Dust accompanied by air pollutants, which were characteristically active in these years. The findings of this study have implications for the use of observational data in validating global aerosol transport models.

Extreme air pollution events in Hokkaido, Japan, traced back to early snowmelt and large-scale wildfires over East Eurasia: Case studies.

To identify the unusual climate conditions and their connections to air pollutions in a remote area due to wildfires, we examine three anomalous large-scale wildfires in May 2003, April 2008, and July 2014 over East Eurasia, as well as how products of those wildfires reached an urban city, Sapporo, in the northern part of Japan (Hokkaido), significantly affecting the air quality. NASA's MERRA-2 (the Modern-Era Retrospective analysis for Research and Applications, Version 2) aerosol re-analysis data closely reproduced the PM2.5 variations in Sapporo for the case of smoke arrival in July 2014. Results show that all three cases featured unusually early snowmelt in East Eurasia, accompanied by warmer and drier surface conditions in the months leading to the fires, inducing long-lasting soil dryness and producing climate and environmental conditions conducive to active wildfires. Due to prevailing anomalous synoptic-scale atmospheric motions, smoke from those fires eventually reached a remote area, Hokkaido, and worsened the air quality in Sapporo. In future studies, continuous monitoring of the timing of Eurasian snowmelt and the air quality from the source regions to remote regions, coupled with the analysis of atmospheric and surface conditions, may be essential in more accurately predicting the effects of wildfires on air quality.