The Seasonal Variations of Aerosols over East Asia as Jointly Inferred from MODIS and OMI

Data on aerosol optical thickness(AOT) and single scattering albedo(SSA) derived from Moderate Resolution Imaging Spectrometer(MODIS) and Ozone Monitoring Instrument(OMI) measurements,respectively,are used jointly to examine the seasonal variations of aerosols over East Asia.The seasonal signals of the total AOT are well defined and nearly similar over the land and over the ocean.These findings indicate a natural cycle of aerosols that originate primarily from natural emissions. In contrast,the small-sized aerosols represented by the fine-mode AOT,which are primarily generated over the land by human activities,do not have evident seasonalscale fluctuations.A persistent maximum of aerosol loadings centered over the Sichuan basin is associated with considerable amounts of fine-mode aerosols throughout the year.Most regions exhibit a general spring maximum. During the summer,however,the aerosol loadings are the most marked over north central China.This occurrence may result from anthropogenic fine particles,such as sulfate and nitrate.Four typical regions were selected to perform a covariation analysis of the monthly gridded AOT and SSA.Over southwestern and southeastern China,if the aerosol loadings are small to moderate they are composed primarily of the highly absorptive aerosols. However,more substantial aerosol loadings probably represent less-absorptive aerosols.The opposite covariation pattern occurring over the coastal-adjacent oceans suggests that the polluted oceanic atmosphere is closely correlated with the windward terrestrial aerosols.North central China is strongly affected by dust aerosols that show moderate absorption.This finding may explain the lower variability in the SSA that accompanies increasing aerosol loadings in this region.

Spatio-temporal Distributions of Tropospheric NO_2 over Oases in Taklimakan Desert, China

Soil biogenic NO emission is one of the most important sources of atmospheric nitrogen oxides(NOx) worldwide. However, the estimation of soil source, especially in arid areas presents large uncertainties because of the substantial lack of measurements. In this study, we selected the Ruoqiang oases on the southeastern edge of the Taklimakan Desert, China as the study area and applied Ozone Monitoring Instrument(OMI) NO2 retrievals(DOMINO v2.0, 2005–2011) to investigate the spatial distribution and seasonal variations in tropospheric NO2 vertical column density(VCD). High NO2 VCDs were observed over the oases(farmlands and natural vegetation), with the highest value obtained during summer, and lowest during winter. Pulses were observed during spring. We conducted in-situ measurements in June 2011 in Milan oasis and employed ground-based multi-axis differential optical absorption spectroscopy(MAX-DOAS) instruments to validate satellite NO2 retrievals. The findings are as follows: 1) in the study area soil biogenic NO emission is the dominant source of tropospheric NO2; 2) oases(farmlands) are hotspots of tropospheric NO2, and a higher increase in tropospheric NO2 is found in oases from winter to summer; and 3) enhancement of soil biogenic NO emission due to soil managements is predictable. Given the rapid agricultural development in the southern Uygur Autonomous Region of Xinjiang, researches on soil biogenic NO emission and increase in tropospheric NOx should be given more importance.

Modeling of spatial and temporal variations of ozone-NO_(x)-VOC sensitivity based on photochemical indicators in China

Comprehensive air quality model with extensions(CAMx)-decoupled direct method(DDM)was used to simulate ozone-NO_(x)-VOCs sensitivity of for May-November in 2016-2018 in China.Based on the relationship between the simulated ozone(O_(3))sensitivity values and the ratio of formaldehyde(HCHO)to NO_(2)(FNR)and the ratio of production rate of hydrogen peroxide(H_(2)O_(2))to production rate of nitric acid(HNO_(3))(P_(H_(2)O_(2))/P_(HNO_(3))),the localized range of FNR and P_(H_(2)O_(2))/P_(HNO_(3))thresholds in different regions in China were obtained.The overall simulated FNR values are about 1.640-2.520,and P_(H_(2)O_(2))/P_(HNO_(3))values are about 0.540-0.830 for the transition regime.Model simulated O_(3)sensitivities or region specific FNR or P_(H_(2)O_(2))/P_(HNO_(3))thresholds should be applied to ensure the accurate local O3 sensitivity regimes.Using the tropospheric column FNR values from ozone monitoring instrument(OMI)satellite data as an indicator with the simulated threshold values,the spatial distributions of O_(3)formation regimes in China are determined.The O_(3)sensitivity regimes from eastern to central China are gradually from VOC-limited,transition to NO_(x)-limited spatially,and moving toward to transition or NO_(x)-limited regime from 2005 to 2019 temporally.

基于OMI资料的中国对流层NO2柱浓度时空变化及其影响因子分析

根据2018年3月至2019年2月OMI遥感反演的三级格点数据,结合土地资源利用、人口密度和国内生产总值(Gross Domestic Product,GDP)等辅助数据,分析了中国对流层NO2垂直柱浓度的时空变化及其影响因子.结果表明:在中国,对流层NO2柱浓度呈现出显著的空间分布差异,体现为东部最高、中部较低、西部最低;NO2柱浓度较大的区域主要集中在华北和华东的"两心一带"地区;中西部也有一些较为分散的高值区,如乌鲁木齐等地;对流层NO2柱浓度也表现出较为明显的季节变化,由高到低大致排序为:冬季>秋季>春季>夏季,而西部地区秋冬季节柱浓度通常低于春夏季节.此外,分析结果还表明,人口密度、工农业废气排放量、交通运输尾气排放以及天气和气候条件是影响NO2柱浓度的关键因素.